The formula for calculating air: oxygen entrainment ratio is given as :
100% − FiO2 = air/oxygen entrainment ratio
Since FiO2 − 21% and the entrainment ratio is already known. Substituting the values in the equation: x = FiO2.

100 − x = 9
x − 21
100 − x = 9(x − 21)
100 − x = 9x − 189
10x = 289
x = 289/10
x = 28.9%

The fall in plasma concentration of a drug with time decreases exponentially in a single compartment pharmacokinetic model (wash-out curve).

A straight line is produced when the logarithm (ln) of a drug’s plasma concentration is plotted against time because a constant proportion of the drug is removed from the plasma per unit time. The line’s gradient or slope can be expressed mathematically as k. (the rate constant). The gradient is related to the half life (T1/2) because it can be used to predict a drug’s plasma concentration at any time.

According to the following formula, clearance (CL), volume of distribution (Vd), and elimination rate constant (k) are mathematically related.

CL = Vd x k

For drug A, CL = 1 x 0.1 = 0.1units per minute

For drug B, Cl = 2 x 0.2 = 0.4 units per minute

Hence, it is proved that Drug A has a lower clearance than drug B.

Absolute risk reduction = (Control event rate) – (Experimental event rate)

Experimental event rate = 24 / 120 = 0.2

Control event rate = 60 / 240 = 0.25

Absolute risk reduction = 0.25 – 0.2 = 0.05 = 5% reduction

The intrinsic pathway is best assessed by the aPTT time.

D-dimer is a fibrin degradation product which is raised in the presence of blood clots.

A 50:50 mixing study is used to assess if a prolonged PT or aPTT is due to factor deficiency or a factor inhibitor.

The thrombin time is a test used to assess fibrin formation from fibrinogen in plasma. Factors that prolong the thrombin time include heparin, fibrin degradation products, and fibrinogen deficiency.

Intrinsic pathway – Best assessed by APTT. Factors 8,9,11,12 are involved. Prolonged aPTT can be seen in haemophilia and use of heparin.

Extrinsic pathway – Best assessed by Increased PT. Factor 7 involved.

Common pathway – Best assessed by APTT & PT. Factors 2,5,10 involved.

Vitamin K dependent factors are factors 2,7,9,10

A prospective randomised double blind controlled trial against cyclizine in multiple centres is the most likely to change your practice.

Case controlled studies are efficient in identifying an association between a drug treatment and outcome and are usually conducted retrospectively. They are generally less valued than prospective randomised trials. They cannot generate incidence data, are subject to bias, have difficult selection of controls and can be made more difficult if note keeping is not reliable.

The gold standard in intervention-based studies is randomised controlled double blind trials. Its features are:

Treating all intervention groups identically
Reduction of bias by random allocation to intervention groups
Patients and researchers unaware of which treatment was given until at completion of study
Patients analysed within the group to which they were allocated, and
Analysis focused on estimating the size of the difference in predefined outcomes between intervention groups.

New healthcare interventions should be evaluated through properly designed randomised controlled trials (though there are some potential ethical disadvantages)

Conducting trials in multiple centres is an accepted way of evaluating a new drug as it may be the only way of recruiting sufficient number of patients within a reasonable time frame to satisfy the objectives of the trial. Type II statistical errors will occur if a small numbers of patients is used in study group.

Adrenaline is released by the adrenal glands, acts on ? 1 and 2, ? 1 and 2 receptors, and is responsible for fight or flight response.

It acts on ? 2 receptors in skeletal muscle vessels-causing vasodilation.

It acts on ? adrenergic receptors to inhibit insulin secretion by the pancreas. It also stimulates glycogenolysis in the liver and muscle, stimulates glycolysis in muscle.

It acts on ? adrenergic receptors to stimulate glucagon secretion in the pancreas
It also stimulates Adrenocorticotrophic Hormone (ACTH) and stimulates lipolysis by adipose tissue

The heart has two venous drainage systems:
1. Greater venous system – it parallels the coronary arterial circulation and provides 70% venous drainage to the heart
2. Lesser venous system – includes the thebasian veins and provides up to 30% of the venous drainage to the heart

Thebasian veins (also called venae cordis minimae) are the smallest coronary veins and run in the myocardial layer of the heart. They serve to drain the myocardium and are present in all four heart chambers. They are more abundant on the right side of the heart and, more specifically, are most abundant in the right atrium. Thebesian veins drain the subendocardial myocardium either directly, via connecting intramural arteries and veins, or indirectly, via subendocardial sinusoidal spaces.

Structural isomers have a similar molecular formula, but they have a different structural formula as their atoms are arranged in a different manner. Such small changes lead to the differential pharmacological activity. Enflurane and isoflurane are two prime examples of structural isomers.

Stereoisomers are those substances that have a similar molecular and structural formula, but the arrangement spatially of atoms are different and have optical activity.

Enantiomers are a pair of stereoisomers, which are non-superimposable mirror images of each other. They also have chiral centres of molecular symmetry. Ketamine is considered as an example of racemic mixture (contain 50% R and 50% S enantiomers)

Geometric isomers contain a carbon-carbon double bond (i.e. C=C) or a rigid carbon-carbon single bond in a heterocyclic ring. Cis-atracurium is one example.

Dynamic isomers or Tautomers are a pait of unstable structural isomers, which are present in equilibrium. One isomer can easily change after the change in pH. Midazolam and thiopentone are their examples.

Cardiac output = stroke volume x heart rate

Left ventricular ejection fraction = (stroke volume / end diastolic LV volume ) x 100%

Stroke volume = end diastolic LV volume – end systolic LV volume

Pulse pressure = Systolic Pressure – Diastolic Pressure

Systemic vascular resistance = mean arterial pressure / cardiac output
Factors that increase pulse pressure include:
-a less compliant aorta (this tends to occur with advancing age)
-increased stroke volume

Approximately 20% of halothane and 0.02% desflurane undergo hepatic biotransformation. Desflurane, halothane, and isoflurane are metabolised in the liver by cytochrome p450 to trifluoroacetate. Through an immunological mechanism involving trifluoroacetyl hapten formation, trifluoroacetate is thought to be responsible for hepatotoxicity.

Potency of inhaled anaesthetic agents is measured using the minimal alveolar concentration (MAC). The MAC of halothane is 0.74% while that of desflurane is 6.3%. The potency can also be compared using the oil: gas partition coefficient (224 and 18.7 for halothane and desflurane respectively).

Onset of action of volatile agents depends on the blood:gas partition coefficient. A lower blood:gas partition coefficient and insolubility in blood means faster onset and offset of action. The blood gas coefficient for halothane is 2.4 while that of desflurane is 0.42. Desflurane is less soluble than halothane in blood. Halothane has a pungent smell that can irritate the airway which limits its use for a gaseous induction especially in paediatric anaesthesia. desflurane is not pungent.

Desfluranes boiling point is only slightly above normal room temperature (22.8°C) making it extremely volatile while the boiling point of halothane is approximately 50.2°C.

The guidelines for the management of cardiac arrest in hypothermic patients published by the UK Resuscitation Council differ slightly from the standard algorithm.

In a patient with a core temperature of less than 30°C, do the following:

If you’re on the shockable side of the algorithm (VF/VT), you should give three DC shocks.
Further shocks are not recommended until the patient has been rewarmed to a temperature of more than 30°C because the rhythm is refractory and unlikely to change.
There should be no drugs given because they will be ineffective.

In a patient with a core temperature of 30°C to 35°C, do the following:

DC shocks are used as usual.
Because they are metabolised much more slowly, the time between drug doses should be doubled.

Active rewarming and protection against hyperthermia should be given to the patient.

Option e is false because there is insufficient information to determine whether resuscitation should be stopped.

Mapleson breathing system (or circuit) analysed five different arrangements of components of the breathing system:
Mapleson A – It is the most efficient for spontaneous respiration. The flow of fresh gas required is 70-85 ml/kg/min, i.e., approximately 5-6 lit./min fresh gas flow for an average adult.
Mapleson B and C – inefficient for both SV and PPV; requires gas flow of two to three times minute volume (100 ml/kg/min). Not commonly used but category C may be used for emergency resuscitation.
Mapleson D – efficient for PPV at gas flow equivalent to patient’s minute volume; the Bain’s circuit is a coaxial version of the Mapleson D
Mapleson E and F – for paediatric use; requires gas flow at two to three times the patient’s minute volume. The Mapleson F consists of an open-ended reservoir bag (Jackson-Rees modification).

There are two types of defibrillators
AC defibrillator
DC defibrillator

AC defibrillator,
consists of a step-up transformer with primary and secondary winding and two switches. Since secondary coil consists of more turns of wire than the primary coil, it induces larger voltage. A voltage value ranging between 250V to 750V is applied for AC external defibrillator. And used to enable the charging of a capacitor.

DC defibrillator,
consists of auto transformer T1 that acts as primary of the high voltage transformer T2. Is an iron core that transfers energy between 2 circuits by electromagnetic induction. Transformers are used to isolate circuits, change impedance and alter voltage output. transformers do not convert AC to DC.

Diode rectifier composed of 4 diodes made of semiconductor material allows current to flow only in one direction. Alternating current (AC) passing through these diodes produces direct current (DC). Capacitor stores the charge in the form of an electrostatic field.

Capacitor is used to convert the rectified AC voltage to produce DC voltage but capacitors do not directly convert AC to DC.

Inductor induces a counter electromotive force(emf) that reduces the capacitor discharge value.

In step-down transformer primary coils has more turns of wire than secondary coil, so induced voltage is smaller in the secondary coil.

The abdominal arteries are divided into 3 branches;
– 3 main unpaired trunks (celiac trunk, superior mesenteric, inferior mesenteric arteries)
– 6 paired branches
– unpaired median sacral artery.

We can group the abdominal aorta as follows;
-Ventral which includes: Coeliac trunk, superior mesenteric and inferior mesenteric arteries
-Lateral: Inferior phrenic, middle suprarenal, renal and gonadal arteries
-Dorsal: Lumbar and median sacral arteries
-Terminal : Right and left common iliac arteries

The celiac trunk (L1) takes blood the foregut and its found posterior to the stomach. The unpaired superior mesenteric artery supplies blood to the mid-gut.

The paired renal arteries form the inferior suprarenal arteries. The renal arteries arise around L1/L2 and takes blood to either side of the kidneys.

The median sacral artery supplies blood to the lumbar vertebrae the L4 and L5.

The larynx is an air passage, sphincter, and organ of phonation that extends from the tongue to the trachea. It lies in the anterior part of the neck at the vertebral levels C3 to C6.

Important anatomical landmarks:
C1-C2 – Atlas and axis, respectively

C3-C6 – Larynx

C5 – Thyroid cartilage

T5-T7 – Pulmonary hilum

T12-L1 – Duodenum

In the Child-Pugh classification system, the following 5 components are determined or calculated in order:

Ascites

Grade of encephalopathy

Serum bilirubin (?mol/L)

Serum Albumin (g/L)

Prothrombin time or INR

Raised liver enzymes are not the component of the classification system.

T3 is produced by peripheral de-iodination of T4. It is more active than T4.

TBG, like most binding proteins, is increased in pregnancy. Because of this, measurement of free thyroid hormone concentration is more important than total.

T4 and T3 concentrations are decreased in Illness and starvation.

L-T4 that is the active molecule while D-T4 is inactive.

ICP is significant because it influences cerebral perfusion pressure and cerebral blood flow. The normal ICP ranges from 5 to 13 mmHg.

The components within the skull include the brain (80%/1400 ml), blood (10%/150 ml), and cerebrospinal fluid (CSF) (10%/150 ml).

Because the skull is a rigid box, if one of the three components increases in volume, one or more of the remaining components must decrease in volume to compensate, or the ICP will rise (Monroe-Kellie hypothesis).

Primary brain injury occurs as a result of a head injury and is unavoidable unless precautions are taken to reduce the risk of head injury. A reduction in oxygen delivery due to hypoxemia (low arterial PaO2) or anaemia, a reduction in cerebral blood flow due to hypotension or reduced cardiac output, and factors that cause a raised ICP and reduced CPP are all causes of secondary brain injury. Secondary brain injury can be avoided with proper management.

The most important initial management task is to make certain that:

There is protection of the airway and the cervical spine
There is proper ventilation and oxygenation
Blood pressure and cerebral perfusion pressure are both adequate (CPP).

Following the implementation of these management principles, additional strategies to reduce ICP and preserve cerebral perfusion are required. The volume of one or more of the contents of the skull can be reduced using techniques that can be used to reduce ICP.

Reduce the volume of brain tissue
Blood volume should be reduced.
CSF volume should be reduced.

The following are some methods for reducing the volume of brain tissue:
Abscess removal or tumour resection
Steroids (especially dexamethasone) are used to treat oedema in the brain.
To reduce intracellular volume, use mannitol/furosemide or hypertonic saline.
To increase intracranial volume, a decompressive craniectomy is performed.

The following are some methods for reducing blood volume:

Haematomas must be evacuated.
Barbiturate coma reduces cerebral metabolic rate and oxygen consumption, lowering cerebral blood volume as a result.
Hypoxemia, hypercarbia, hyperthermia, vasodilator drugs, and hypotension should all be avoided in the arterial system.
PEEP/airway obstruction/CVP lines in neck: patient positioning with 30° head up, avoid neck compression with ties/excessive rotation, avoid PEEP/airway obstruction/CVP lines in neck

The following are some methods for reducing CSF volume:

To reduce CSF volume, an external ventricular drain or a ventriculoperitoneal shunt is inserted (although more a long term measure).

The drug of choice for the treatment of anaphylaxis is adrenaline. It has an intravenous route of administration. Since the patient already has intravenous access, the intramuscular route is not appropriate.

Second-line pharmacological intervention includes the use of chlorpheniramine 10mg intravenous, Hydrocortisone 200mg.

The most likely diagnosis is a spinal epidural haematoma, a neurological emergency. A full examination must be carried out to determine the nature of the neurological problem before conducting any investigations or imaging.

The effects of spinal anaesthesia should have worn off by this time point, and the severe back pain is a red flag.

The patient will also require an urgent neurological team referral as a spinal epidural haematoma requires immediate evacuation for spinal decompression. Analgesics may be prescribed for pain management.

Heparin would have been fully metabolised and so a reversal is unnecessary.

A spinal epidural haematoma is a pooling of blood in the epidural space, which can cause compression of the spinal cord. Its presenting symptoms are:

Usually begins with severe backpain and percussion tenderness
Cauda equina syndrome
Paralysis of the lower extremities.
If infected, a fever occurs in 66% of cases
Lower limb weakness developing after stopping an epidural infusion or weakness of the lower limbs which does not resolve within four hours of cessation of infusion of epidural local anaesthetic
Meningism.

With regards to compensatory response to blood loss, the following sequence of events take place:

1. Decrease in venous return, right atrial pressure and cardiac output
2. Baroreceptor reflexes (carotid sinus and aortic arch) are immediately activated
3. There is decreased afferent input to the cardiovascular centre in medulla. This inhibits parasympathetic reflexes and increases sympathetic response
4. This results in an increased cardiac output and increased SVR by direct sympathetic stimulation. There is increased circulating catecholamines and local tissue mediators (adenosine, potassium, NO2)
5. Fluid moves into the intravascular space as a result of decreased capillary hydrostatic pressure absorbing interstitial fluid.

A slower response is mounted by the hypothalamus-pituitary-adrenal axis.
6. Reduced renal blood flow is sensed by the intra renal baroreceptors and this stimulates release of renin by the juxta-glomerular apparatus.
7. There is cleavage of circulating Angiotensinogen to Angiotensin I, which is converted to Angiotensin II in the lungs (by Angiotensin Converting Enzyme ACE)

Angiotensin II is a powerful vasoconstrictor that sets off other endocrine pathways.
8. The adrenal cortex releases Aldosterone
9. There is antidiuretic hormone release from posterior pituitary (also in response to hypovolaemia being sensed by atrial stretch receptors)
10. This leads to sodium and water retention in the distal convoluted renal tubule to conserve fluid
Fluid conservation is also aided by an increased amount of cortisol which is secreted in response to the increase in circulating catecholamines and sympathetic stimulation.

Propranolol is a nonselective beta-blocker with a half-life of 3 to 6 hours.

Since it is lipid-soluble it crosses the blood-brain barrier and causes Central Nervous System side effects like sedation, nightmares, and depression.

They are contraindicated in asthma, Congestive heart failure, and diabetes.

It has a large volume of distribution with no intrinsic sympathomimetic action.

Noradrenaline also called norepinephrine belongs to the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter.

They have sympathomimetic effects acting via adrenoceptors (?1, ?2,?1, ?2, ?3) or dopamine receptors (D1, D2).

May cause reflex bradycardia, reduce cardiac output and increase myocardial oxygen consumption

Iron is a necessary micronutrient for proper erythropoietic function, oxidative metabolism, and cellular immune responses. Although dietary iron absorption (1-2 mg/d) is tightly controlled, it is only just balanced by losses.

The adult body contains 35-45 mg/kg iron (about 4-5 g)

Iron can be found in a variety of forms, including haemoglobin, ferritin, haemosiderin, myoglobin, haem enzymes, and transferrin bound proteins.

The inguinal canal is a passage in the lower anterior abdominal wall just above the inguinal ligament. It transmits the following structures:
1. genital branch of genitofemoral nerve
2. ilioinguinal nerve
3. spermatic cord (males only)
4. round ligament of the uterus (females only)

The ilioinguinal is a direct branch of the first lumbar nerve. The ilioinguinal nerve enters the inguinal canal via the abdominal musculature (and not through the deep (internal) inguinal ring) and exits through the superficial (or external) inguinal ring.

The openings for the other nerves in the answer options are:
Sciatic nerve – exits the pelvis via the greater sciatic foramen
Obturator nerve – descends into pelvis via the obturator foramen
Femoral nerve – descends from the abdomen through the pelvis behind the inguinal canal

The Iliohypogastric nerve also arises from the first lumbar root with the ilioinguinal nerve but pierces the transversus abdominis muscle posteriorly, just above the iliac crest, and continues anteriorly between the transversus abdominis and the internal abdominal oblique muscles.

Sixty-seven percent of filtered water is reabsorbed in the proximal tubule. The driving force for water reabsorption is a transtubular osmotic gradient established by reabsorption of solutes (e.g., NaCl, Na+-glucose).

Henle’s loop reabsorbs approximately 25% of filtered NaCl and 15% of filtered water. The thin ascending limb reabsorbs NaCl by a passive mechanism, and is impermeable to water. Reabsorption of water, but not NaCl, in the descending thin limb increases the concentration of NaCl in the tubule fluid entering the ascending thin limb. As the NaCl-rich fluid moves toward the cortex, NaCl diffuses out of the tubule lumen across the ascending thin limb and into the medullary interstitial fluid, down a concentration gradient as directed from the tubule fluid to the interstitium. This mechanism is known as the counter current multiplier.

The distal tubule and collecting duct reabsorb approximately 8% of filtered NaCl, secrete variable amounts of K+ and H+, and reabsorb a variable amount of water (approximately 8%-17%).

The electrical conduction system of the heart starts with the SA node which generates spontaneous action potentials.

This is conducted across both atria by cell to cell conduction, and occurs at around 1 m/s. The only pathway for the action potential to enter the ventricles is through the AV node in a normal heart.
At this site, conduction is very slow at 0.05ms, which allows for the atria to completely contract and fill the ventricles with blood before the ventricles depolarise and contract.

The action potentials are conducted through the Bundle of His from the AV node which then splits into the left and right bundle branches. This conduction is very fast, (,2m/s), and brings the action potential to the Purkinje fibres.

Purkinje fibres are specialised conducting cells which allow for a faster conduction speed of the action potential (,2-4m/s). This allows for a strong synchronized contraction from the ventricle and thus efficient generation of pressure in systole.

In contrast to the arterial system, which contains 15% of the circulating blood volume, the body’s veins contain 70% of it.

In severe haemorrhage, when sympathetic stimulation causes venoconstriction, venous tone is important in maintaining the return of blood to the heart.

Because the liver receives about 30% of the resting cardiac output, it is a very vascular organ. The hepatic vascular system is dynamic, which means it can store and release blood in large amounts – it acts as a reservoir within the general circulation.

In a normal situation, the liver contains 10-15% of total blood volume, with the sinusoids accounting for roughly 60% of that. The liver dynamically adjusts its blood volume when blood is lost and can eject enough blood to compensate for a moderate amount of haemorrhage.

In the portal venous and hepatic arterial systems, sympathetic nerves constrict the presinusoidal resistance vessels. More importantly, sympathetic stimulation lowers the portal system’s capacitance, allowing blood to flow more efficiently to the heart.

Net transcapillary absorption of interstitial fluid from skeletal muscle into the intravascular space compensates for blood loss effectively during haemorrhage. The decrease in capillary hydrostatic pressure (Pc), caused by reflex adrenergic readjustment of the ratio of pre- to postcapillary resistance, is primarily responsible for fluid absorption. Within a few hours of blood loss, these fluid shifts become significant, further diluting haemoglobin and plasma proteins.

Albumin synthesis begins to increase after 48 hours.

The juxtamedullary complex releases renin in response to a drop in mean arterial pressure, which causes an increase in aldosterone level and, eventually, sodium and water resorption. Increased antidiuretic hormone (ADH) levels also contribute to water retention.

Compliance of the respiratory system describes the expandability of the lungs and chest wall. There are two types of compliance: dynamic and static.

Dynamic compliance describes the compliance measured during breathing, which involves a combination of lung compliance and airway resistance. Defined as the change in lung volume per unit change in pressure in the presence of flow.

Static compliance describes pulmonary compliance when there is no airflow, like an inspiratory pause. Defined as the change in lung volume per unit change in pressure in the absence of flow.

For example, if a person was to fill the lung with pressure and then not move it, the pressure would eventually decrease; this is the static compliance measurement. Dynamic compliance is measured by dividing the tidal volume, the average volume of air in one breath cycle, by the difference between the pressure of the lungs at full inspiration and full expiration. Static compliance is always a higher value than dynamic

Static compliance can be computed using the formula:

Cstat = Tidal volume/Plateau pressure – PEEP

Substituting the values given,

Cstat = 800/50-10
Cstat = 20 ml/cmH2O

The arterial blood gas analysis indicates presence of acute respiratory acidosis.

Central chemoreceptors are located in the ventral medulla and respond directly to presence of hydrogen ions in the CSF. When stimulated, it causes an increase in respiratory rate.

It is believed that hydrogen ions may be the only important direct stimulus for these neurons, however, CO2 is believed to stimulate these neurons secondarily by changing the hydrogen ion concentration.

Changes in O2 concentration have virtually no direct effect on the respiratory centre itself to alter respiratory drive. Although, O2 changes do have an indirect effect by acting through the peripheral chemoreceptors.

Increasing temperature increases the amount of water vapour contained in air; for example, at 20°C, air contains about 17 g/m3, and at 37°C, air contains about 44 g/m3. The wet and dry bulb hygrometer, like the hair hygrometer, measures relative humidity.

Under normal operating conditions, Heat and moisture exchangers (HMEs) allows relative humidity of up to 70% to be achieved. Mucus can impair their performance, and they should not be used for longer than 24 hours.

Hot water bath humidifiers might cause scalding, condensed water in the tubing can interfere with gas flow, and there is a danger of infection.

The ultrasonic humidifier operates at roughly 2 MHz and may attain relative humidity levels much above 100%.

The superficial inguinal ring is an opening in the aponeurosis of the external oblique muscle, just above and lateral to the pubic crest.

The superficial ring resembles a triangle more than a ring with the base lying on the pubic crest and its apex pointing towards the anterior superior iliac spine. The sides of the triangle are crura of the opening in the external oblique aponeurosis. The lateral crura of the triangle is attached to the pubic tubercle. The medial crura of the triangle is attached to the pubic crest.

The external oblique aponeurosis forms the anterior wall of the inguinal canal and also the lateral edge of the superficial inguinal ring. The rectus abdominis lies posteromedially, and the transversalis posterior to this.

The femoral triangle is a wedge-shaped area found within the superomedial aspect of the anterior thigh. It is a passageway for structures to leave and enter the anterior thigh.

Superior: Inguinal ligament
Medial: Adductor longus
Lateral: Sartorius
Floor: Iliopsoas, adductor longus and pectineus

The contents include: (medial to lateral)
Femoral vein
Femoral artery-pulse palpated at the mid inguinal point
Femoral nerve
Deep and superficial inguinal lymph nodes
Lateral cutaneous nerve
Great saphenous vein
Femoral branch of the genitofemoral nerve

Resistance pulmonary arteries constrict in response to alveolar and airway hypoxia, diverting blood to better-oxygenated alveoli.

In atelectasis, pneumonia, asthma, and adult respiratory distress syndrome, hypoxic pulmonary vasoconstriction optimises O2 uptake. Hypoxic pulmonary vasoconstriction helps maintain systemic oxygenation during single-lung anaesthesia.

A redox-based O2 sensor within pulmonary artery smooth muscle cells is involved in hypoxic pulmonary vasoconstriction. The production of reactive oxygen species by smooth muscle cells in the pulmonary artery varies in proportion to PaO2. Hypoxic removal of these redox second messengers inhibits voltage-gated potassium channels, depolarizing smooth muscle cells in the pulmonary artery.

L-type calcium channels are activated by depolarization, which raises cytosolic calcium and causes hypoxic pulmonary vasoconstriction. Some anaesthetics suppress this response, increasing the risk of further deterioration in ventilation perfusion mismatch.

Agents that inhibit HPV are ether, halothane, and desflurane (>1.6 MAC).
Agents with no effect on HPV include thiopentone, fentanyl, desflurane (1MAC), isoflurane (<1.5MAC), sevoflurane(1MAC), and propofol.

Since the data is normally distributed, 95% of the values lie with in the interval 70 to 90. This can be calculated as follows:

Interval= Mean ± ( 2 times standard deviation)
= 80 ± 2(5)
= 80 ± 10
= 70 & 90

The rest of the 5% are distributed symmetrically beyond 90 and below 70 which means 2.5% of the values lie above 90.

Calcium is a very important ion and is involved in:
-cell homeostasis
-coagulation
-muscle contraction
-neuronal impulse transmission/membrane stabilization
-bone formation and skeletal strength
-secretion processes

99% is found in bone and 1% in the plasma. Of the 1% that is in the plasma
-45% is free ionized calcium
-45% is bound to proteins, mainly Albumin
-10% is present as an anion complex

Reduced levels of IONIZED calcium give rise to features of hypocalcaemia , resulting in increased excitability of membranes. This results when the total calcium concentration goes below 2 mmol/L.

Features of mild to moderate hypocalcaemia are:
-paraesthesia (peri-oral, fingers)
-tetany
-spasm
-muscle cramps
-ECG changes (prolonged QT)
-Trousseau’s sign (inflation of tourniquet induces carpopedal spasm)
-Chvostek’s sign (tapping the facial nerve – cranial nerve VII – causes facial muscle twitch/spasm)

Features of severe hypocalcaemia are:
-cardiogenic shock and congestive cardiac failure due to reduced myocardial contractility
respiratory distress due to bronchospasm, agitation, confusion, seizures

Features of hypercalcaemia (remember ‘bones, stones, groans and psychic moans’):
-Abdominal pain
-Vomiting
-Constipation
-Polyuria
-Polydipsia
-Depression
-Lethargy
-Anorexia
-Weight loss
-Hypertension
-Confusion
-Pyrexia
-Calcification in the cornea
-Renal stones
-Renal failure
-Decreased Q-T interval
-Cardiac shock/collapse

Glyceryl trinitrate (GTN) has a significant first pass metabolism. About 90% of a dose of GTN is metabolised in the liver by the enzyme glutathione organic nitrate reductase.

An INSIGNIFICANT amount of metabolism occurs in the intestinal mucosa.

There is approximately 1% bioavailability after oral administration and 38% after sublingual administration.

GTN does NOT cause gastric irritation and it is well absorbed in the gastrointestinal tract.

The volume of distribution of GTN is 2.1 to 4.5 L/kg. This is HIGH.

Cephalosporin belongs to a family of beta-lactam antibiotics. All ?-lactam antibiotics interfere with the synthesis of the bacterial cell walls. The ?-lactam antibiotics inhibit the transpeptidases so that cross-linking (which maintains the close-knit structure of the cell wall) does not take place i.e. they inhibit bacterial cell wall formation.

Flowmeters measure the rate at which a specific gas, that the flowmeter has been calibrated for, passes through. This calibration is done at room temperature and standard atmospheric pressure with an accuracy of +/- 2%.

Reading the flowmeter is done from the top of a bobbin (the midpoint of a ball). Oxygen is the last gas to be added downstream to the mixture delivered to the back bar as a safety feature. This prevents delivery of a hypoxic mixture.

Inaccurate flow measurements occur when the bobbin sticks to the inside wall of the flowmeter. Stannic oxide has been used as a successful antistatic substance thus, reducing the aforementioned risk.

Carbon dioxide being easily delivered is found on some older machines, but those attached flowmeters are limited by a maximum flow of 500 ml /min. Thus avoiding the delivery of a hypercarbic mixture.

Noradrenaline has a short half-life of about 2 minutes. It is rapidly cleared from plasma by a combination of cellular reuptake and metabolism.

It acts as sympathomimetics by acting on ?1 receptors and also on ? receptors.

It decreases renal and hepatic blood flow.

Norepinephrine is metabolized by the enzymes monoamine oxidase and catechol-O-methyltransferase to 3-methoxy-4-hydroxymandelic acid and 3-methoxy-4-hydroxyphenylglycol (MHPG).

Natural catecholamines are Adrenaline, Noradrenaline, and Dopamine

The Weibull distribution are used to describe various types of observed failures of the components. it is used in reliability and survival analysis.

Regression Analysis is used to measure the relationship between among two or more variable. It determines the effect of independent variables on the dependent variables.

Student t-test is one of the most commonly used method to test the hypothesis. It determines the significant difference between the means of two different groups.

A time series is a collection of observations of well-defined data obtained at regular interval of time.

Kaplan-Meier estimator is used to estimate the survival function from lifetime data. It can be derived from maximum likelihood estimation of hazard function. It is most likely used to measure the fraction of patient’s life for a certain amount of time after treatment.

End-tidal carbon dioxide (ETCO2) monitoring has been an important factor in reducing anaesthesia-related mortality and morbidity. Hypercarbia, or hypercapnia, occurs when levels of CO2 in the blood become abnormally high (Paco2 >45 mm Hg). Hypercarbia is confirmed by arterial blood gas analysis. When using capnography to approximate Paco2, remember that the normal arterial–end-tidal carbon dioxide gradient is roughly 5 mm Hg. Hypercarbia, therefore, occurs when PETco2 is greater than 40 mm Hg.

The most likely explanation for the changes in capnograph is either exhaustion of the soda lime and a progressive rise in circuit dead space.

Inspect the soda lime canister for a change in colour of the granules. To overcome soda lime exhaustion, the first step is to increase the fresh gas flow (FGF) (Option A). Then, if need arises, replace the soda lime granules. Other strategies that can work are changing to another circuit or bypassing the soda lime canister, but remember that both these strategies are employed only after increasing FGF first. Exclude other causes of equipment deadspace too.

There are also other causes for hypercarbia to develop intraoperatively:
1. Hypoventilation is the most common cause of hypercapnia. A. Inadequate ventilation can occur with spontaneous breathing due to drugs like anaesthetic agents, opioids, residual NMDs, chronic respiratory or neuromuscular disease, cerebrovascular accident.
B. In controlled ventilation, hypercapnia due to circuit leaks, disconnection or miscalculation of patient’s minute volume.
2. Rebreathing – Soda lime exhaustion with circle, inadequate fresh gas flow into Mapleson circuits and increased breathing system deadspace.
3. Endogenous source – Tourniquet release, hypermetabolic states (MH or thyroid storm) and release of vascular clamps.
4. Exogenous source – Absorption of CO2 from pneumoperitoneum.

Colligative properties are properties of solutions that depend on the number of dissolved particles in solution. They do not depend on the identities of the solutes.

All of the above have colligative properties with the exception of depression of melting point.

The osmolality from the concentration of a substance in a solution is measured by an osmometer. The freezing point of a solution can determines concentration of a solution and this can be measured by using a freezing point osmometer. This is applicable as depression of freezing point is directly correlated to concentration.

Vapour pressure osmometers, which measure vapour pressure, may miss certain volatiles such as CO2, ammonia and alcohol that are in the solution

The use of a freezing point osmometer provides the most accurate and reliable results for the majority of applications.

Colligative properties does not include melting point depression . Mixtures of substances in which the liquid phase components are insoluble, display a melting point depression and a melting range or interval instead of a fixed melting point.

The magnitude of the melting point depression depends on the mixture composition.

The melting point depression is used to determine the purity and identity of compounds. EMLA (eutectic mixture of local anaesthetics) cream is a mixture of lidocaine and prilocaine and is used as a topical local anaesthetic. The melting point of the combined drugs is lower than that individually and is below room temperature (18°C).

The relative risk (also known as risk ratio [RR]) is the ratio of risk of an event in one group (e.g., exposed group) versus the risk of the event in the other group (e.g., nonexposed group).

The odds ratio (OR) is the ratio of odds of an event in one group versus the odds of the event in the other group.

Breathing system is an assembly of components which connects patient’s airway to anaesthesia machine through which controlled composition of gas mixture is dispensed. It delivers gas to the patient, removes expired gas and controls the temperature and humidity of the inspired mixture. It allows spontaneous, controlled, or assisted respiration. It may also provide ports for gas sampling, airway pressure, flow and volume monitoring.

Breathing systems have been classified by Conway and Mapleson.
Conway suggested a functional classification:
– Circuits requiring a CO2 absorber
– Circuits not requiring a CO2 absorber

William Mapleson designated varying arrangements of breathing system components (masks, breathing tubes, fresh gas flow inlets, adjustable pressure-limiting valves, and reservoir bags) as Mapleson A-E circuits.
Mapleson A: Arranged as FGF inlet, reservoir bag, APL valve, mask.
In this circuit, because the reservoir bag is between the FGF inlet valve and the APL valve, expired gas from the patient may re-enter the system and fill the reservoir bag during controlled ventilation. This is the most efficient system for spontaneous breathing as the FGF must only be equal to a patient’s minute ventilation to prevent rebreathing.

Mapleson B: Arranged as reservoir bag, FGF inlet, APL valve, mask.
In this circuit, the FGF inlet is closer to the APL valve, which helps prevent the rebreathing concern in the Mapleson A circuit as above during controlled ventilation.

Mapleson C: Arranged as reservoir bag, FGF inlet, APL valve, mask.
In this circuit, the arrangement is the same as the Mapleson B circuit. However, this circuit is shorter as it does not contain elongated corrugated tubing. This circuit also has the FGF inlet close to the APL valve to aid in preventing rebreathing.

Mapleson D: Arranged as reservoir bag, APL valve, FGF inlet, and mask.
In this circuit, the arrangement interchanges the FGF inlet and APL valve of the Mapleson A circuit. This system prevents rebreathing by directing FGF towards the APL valve rather than towards the patient during exhalation.

Mapleson E: Arranged as corrugated tubing, FGF inlet, and mask.
In this circuit, there is no reservoir bag and no APL valve. Given the inability to alter the pressure of the circuit, this is ideal for spontaneously ventilating neonates or paediatric patients where low-pressure ventilation is desired. The system prevents rebreathing, similar to the Mapleson D circuit.

Jackson Rees later modified the Mapleson E by adding an open ended bag, which has since become known as the Mapleson F.
Mapleson F: Arranged as APL valve directly connected to reservoir bag, corrugated tubing, FGF inlet, and mask.
The system prevents rebreathing similarly to Mapleson D by directing FGF towards the APL valve.

Dopamine (DA) is a dopaminergic (D1 and D2) as well as adrenergic ? and?1 (but not ?2 ) agonist.

The D1 receptors in renal and mesenteric blood vessels are the most sensitive: i.v. infusion of a low dose of DA dilates these vessels (by raising intracellular cAMP). This increases g.f.r. In addition, DA exerts a natriuretic effect by D1 receptors on proximal tubular cells.

Moderately high doses produce a positive inotropic (direct?1 and D1 action + that due to NA release), but the little chronotropic effect on the heart.

Vasoconstriction (?1 action) occurs only when large doses are infused.

At doses normally employed, it raises cardiac output and systolic BP with little effect on diastolic BP. It has practically no effect on nonvascular ? and ? receptors; does not penetrate the blood-brain barrier—no CNS effects.

Dopamine is used in patients with cardiogenic or septic shock and severe CHF wherein it increases BP and urine outflow.

It is administered by i.v. infusion (0.2–1 mg/min) which is regulated by monitoring BP and rate of urine formation

Decreased stroke volume causes decreased ejection fraction which results in diastolic dysfunction.
Ejection fraction is not a useful measure in someone with diastolic dysfunction because stroke volume may be reduced whilst end-diastolic volume may be reduced.
Diastolic dysfunction may arise with reduced heart compliance.

Ejection fraction measures of the proportion of blood leaving the ventricles with each beat and is calculated as follows:
Stroke volume / end-diastolic volume.

A healthy ejection fraction is usually taken as 60% (based on a stroke volume of 70ml and end-diastolic volume of 120ml).

Respiratory inspiration causes a decreased pressure in the thoracic cavity, which in turn causes more blood to flow into the atrium.

Sitting up decreases venous because of the action of gravity on blood in the venous system.
Hypotension also decreases venous return.
A less compliant aorta, like in aortic stenosis increases end systolic left ventricular volume which decreases stroke volume.

Systemic vascular resistance = mean arterial pressure / cardiac output.
Increased vascular resistance impedes the flow of blood back to the heart.

Increased venous return increases end diastolic LV volume as there is more blood returning to the ventricles.

Because enflurane is much less soluble in blood and has a blood: gas partition coefficient of 1.8, both wash-in and wash-out should be faster.

Sevoflurane’s sweet-smelling, non-irritant nature, combined with a low blood: gas partition coefficient, would result in similar offset and onset characteristics.

Isoflurane and enflurane have a molecular weight of 184.

The oil: gas partition coefficient on a volatile agent is a measure of lipid solubility, potency, and thus MAC. Halothane has an oil: gas partition coefficient of 220 and a MAC of 0.74. One would expect the MAC to be higher with an oil gas partition coefficient of 180 (less lipid soluble).

The conversion of halothane (20%) to trifluoroacetic acid via oxidative metabolism has been linked to the development of hepatitis.

P450 2E1 converts sevoflurane to hexafluoroisopropanol, which results in the release of inorganic fluoride ions. It’s the only fluorinated volatile anaesthetic that doesn’t break down into trifluoracetic acid.

Desflurane is likely to cause airway irritation, which can lead to coughing, apnoea, and laryngospasm, despite its low blood:gas partition coefficient (0.42).

The Glasgow Coma Scale (GCS) has been used in outcome models as a measure of physiological derangement and as a tool for assessing head trauma.

Eye opening (E):

4 Spontaneously
3 Responds to voice
2 Responds to painful stimulus
1 No response.

Best verbal response (V):

5 Orientated, converses normally
4 Confused, disoriented conversation, but able to answer basic questions
3 Inappropriate responses, words discernible
2 Incomprehensible speech
1 Makes no sounds.

Best motor response (M):

6 Obeys commands for movement
5 Purposeful movement to painful stimulus
4 Withdraws from pain
3 Abnormal (spastic) flexor response to painful stimuli, decorticate posture
2 Extensor response to painful stimuli, decerebrate posture
1 No response.

In this case, GCS = 2+3+5 = 10.

The amount of oxygen carried by 100 ml of blood is called the arterial oxygen content (CaO2)and is normally 17-24 ml/dL and can be determined by this equation:

CaO2 = oxygen bound to haemoglobin + oxygen dissolved in plasma

CaO2 = (1.34 × Hgb × SaO2 × 0.01) + (0.003 × PaO2)

where:

1.34 = Huffner’s constant (D) – Huffner’s constant does not change and its magnitude relatively small.
Hgb is the haemoglobin level in g/dL and SaO2 is the percent oxyhaemoglobin saturation of arterial blood
PaO2 is (0.0225 = ml of O2 dissolved per 100 ml plasma per kPa, or 0.003 ml per mmHg).

Quantitatively, the amount of oxygen dissolved in plasma is 0.3 mL/dL.

Henry’s law states that at constant temperature, the amount of gas dissolved at equilibrium in a given quantity of a liquid is proportional to the pressure of the gas in contact with the liquid.

Given a haemoglobin concentration of 15 g/dL and a SaO2 of 100% and a PaO2 of 13.3 kPa, the amount of oxygen bound to haemoglobin is 20.4 mL/100mL.

Cardiac output is an important determinant of oxygen delivery but does not influence the oxygen content of blood.

The hindgut is from the distal third of the transverse colon down to the upper one-third of the anal canal. The inferior mesenteric artery supplies the hindgut.

The inferior mesenteric artery arises from the aorta behind the inferior border of the third part of the duodenum 3–4 cm above the aortic bifurcation, at the third lumbar vertebra level.

The important landmarks of vessels arising from the abdominal aorta at different levels of vertebrae are:

T12 – Coeliac trunk

L1 – Left renal artery

L2 – Testicular or ovarian arteries

L3 – Inferior mesenteric artery

L4 – Bifurcation of the abdominal aorta

Oxygen is formed by a molecule of oxygen and two molecules of hydrogen with a molecular formula of H2O

The critical temperature is defined as a temperature above which the substance cannot be liquefied, no matter how much pressure is applied.
Water has a critical temperature of -118.6oC. So, it cannot be liquified at room temperature.

Medical oxygen cylinder is stored in a cylinder with a white shoulder and black body. Meanwhile, medial air is stored in cylinders with a white and black shoulder and a French grey body.

The partial pressure of air at a high altitude is less but the relative concentration remains constant.

Even though aprotinin reduces fibrinolysis and therefore bleeding, there is an associated increased risk of death. It was withdrawn in 2007.
Protein C is dependent upon vitamin K and this may paradoxically increase the risk of thrombosis during the early phases of warfarin treatment.

The coagulation cascade include two pathways which lead to fibrin formation:
1. Intrinsic pathway – these components are already present in the blood
Minor role in clotting
Subendothelial damage e.g. collagen
Formation of the primary complex on collagen by high-molecular-weight kininogen (HMWK), prekallikrein, and Factor 12
Prekallikrein is converted to kallikrein and Factor 12 becomes activated
Factor 12 activates Factor 11
Factor 11 activates Factor 9, which with its co-factor Factor 8a form the tenase complex which activates Factor 10

2. Extrinsic pathway – needs tissue factor that is released by damaged tissue)
In tissue damage:
Factor 7 binds to Tissue factor – this complex activates Factor 9
Activated Factor 9 works with Factor 8 to activate Factor 10

3. Common pathway
Activated Factor 10 causes the conversion of prothrombin to thrombin and this hydrolyses fibrinogen peptide bonds to form fibrin. It also activates factor 8 to form links between fibrin molecules.

4. Fibrinolysis
Plasminogen is converted to plasmin to facilitate clot resorption

There are different types of temperature measurement. These include:

Thermistor – this is a type of semiconductor, meaning they have greater resistance than conducting materials, but lower resistance than insulating materials. There are small beads of semiconductor material (e.g. metal oxide) which are incorporated into a Wheatstone bridge circuit. As the temperature increases, the resistance of the bead decreases exponentially

Thermocouple – Two different metals make up a thermocouple. Generally, in the form of two wires twisted, welded, or crimped together. Temperature is sensed by measuring the voltage. A potential difference is created that is proportional to the temperature at the junction (Seebeck effect)

Platinum resistance thermometers (PTR) – uses platinum for determining the temperature. The principle used is that the resistance of platinum changes with the change of temperature. The thermometer measures the temperature over the range of 200°C to1200°C. Resistance in metals show a linear increase with temperature

Tympanic thermometers – uses infrared radiation which is emitted by all living beings. It analyses the intensity and wavelength and then transduces the heat energy into a measurable electrical output

Gauge/dial thermometers – Uses coils of different metals with different co-efficient of expansion. These either tighten or relax with changes in temperature, moving a lever on a calibrated dial.

Standard error can be calculated by the following formula:

Standard Error= (Standard Deviation)/√(Sample Size)
= (12) / √(64)
= 12 / 8
= 1.5

Every surgical procedure is associated with a stress response which comprises a number of endocrine, metabolic, and immunological changes triggered by neuronal activation of the hypothalamic-pituitary-adrenal axis. The overall metabolic effect of the stress response to surgery includes an increase in secretion of catabolic hormones, such as cortisol and catecholamine, and a decrease in secretion of anabolic hormones, such as insulin and testosterone. The increase in levels of catabolic hormones in plasma stimulates glucose production, and there is a relative lack of insulin together with impaired tissue insulin sensitivity and glucose utilization, which is called insulin resistance. Consequently, blood glucose concentrations will increase, even in the absence of pre-existing diabetes.

A study compared the effects of spinal and general anaesthesia on changes in blood glucose concentrations during surgery in nondiabetic patients. Although mean blood glucose concentrations showed a significant proportional increase during surgery in both groups, this effect was much more significant with general anaesthesia than with spinal anaesthesia. These results indicate that spinal anaesthesia is more effective than general anaesthesia in attenuating the hyperglycaemic response to surgery.

Prostacyclin is a strong vasodilator. It is administered as an intravenous infusion for critical ischemia. Commercially, it is available as sodium epoprodtenol.

Atrial Natriuretic peptide (ANP) hormone secreted from the atria, kidney, and neural tissues. It primarily acts on renal vessel to maintain normal blood pressure and reduce plasma volume by: increasing the renal excretion of salt and water, glomerular filtration rate, vasodilation, and by increasing the vascular permeability. It also inhibits the release of renin and aldosterone.

Indoramin is an alpha-adrenoceptor blocking agent. which act selectively on post-synaptic-alpha adrenoreceptor, leading to decease in peripheral resistance.

Angiotensin II is a vasoconstrictor, causing high sodium retention. It also increases the secretion of antidiuretic hormone (ADH) and aldosterone level.

The renal effects of atrial natriuretic peptide (ANP) secretion are as follows:

Increased glomerular filtration rate by dilating the afferent glomerular arteriole. Moreover, it constricts the efferent glomerular arteriole, and relaxes the mesangial cells.
Reduces sodium reabsorption in the collecting ducts and distal convoluted tubule.
The renin-angiotensin system (RAS) is inhibited.
Blood flow in the vasa recta is increased.

Because plasma osmolality is unlikely to change, hypothalamic osmoreceptors are unaffected.

The plasma protein has a molecular weight of 66 kDa, is not normally filtered into the proximal convoluted tubule, and has no osmotic diuretic effect.

The following are some basic assumptions:

Extracellular fluid (ECF) makes up one-third of total body water (TBW), while intracellular fluid makes up the other two-thirds (ICF)
One-quarter plasma and three-quarters interstitial fluid make up ECF (ISF)
The volume receptors in the atria have a 7-10% blood volume change threshold.
The osmoreceptors are sensitive to changes in osmolality of 1-2 percent.
The normal plasma osmolality before the transfusion is 287-290 mOsm/kg.
The plasma protein solution is a colloid that is only delivered to the intravascular compartment. The tonicity remains unchanged.
The blood volume increases by 20%, from 5,000 mls to 6,000 mls. This is higher than the volume receptor threshold of 7 to 10%.

An ipsilateral phrenic nerve block will result from a successful interscalene block (ISB).

The phrenic nerve is the diaphragm’s sole motor supply, and ipsilateral hemidiaphragmatic paresis affects up to 100% of patients who receive ISBs. Phrenic nerve palsy is usually well tolerated and goes unnoticed by healthy people. However, forced vital capacity decreases by approximately 25%, which can produce ventilatory compromise in patients with limited pulmonary reserve, requiring assisted ventilation.

Vocal cord palsy occurs when the recurrent laryngeal nerve is inadvertently blocked, causing hoarseness and possibly acute respiratory insufficiency. Unless bilateral laryngeal nerve palsy occurs, which can cause severe laryngeal obstruction, this complication is usually of little consequence.

ISB can also cause cranial nerve X and XII palsy (Tapia’s syndrome). One-sided cord paralysis, aphonia, and the patient’s tongue deviating toward the block’s side are all symptoms.

When a local anaesthetic spreads to the stellate ganglion and its cervical sympathetic nerves, Horner’s syndrome can develop. Ptosis of the eyelid, miosis, and anhidrosis of the face are all symptoms. Horner’s syndrome, on the other hand, may not indicate that the brachial plexus is sufficiently blocked.

Erythromycin binds to the 50s subunit of bacterial rRNA complex and inhibits protein synthesis.

Gentamicin is a broad-spectrum antibiotic whose mechanism of action involves inhibition of protein synthesis by binding to 30s ribosomes. Its major adverse effect is nephrotoxicity and ototoxicity

Aminoglycoside bind to 30s subunit of ribosome causing misreading of mRNA

Tetracyclines inhibit protein synthesis through reversible binding to bacterial 30s ribosomal subunits, which prevent binding of new incoming amino acids (aminoacyl-tRNA) and thus interfere with peptide growth.

The pectinate muscles (musculi pectinati) are parallel muscular ridges that extend anterolaterally on the right atrial walls. The most prominent pectinate muscle, which forms the bridge of the sulcus terminalis internally, is the taenia sagittalis (second crest or septum spurium).

In the left atrium, the pectinate muscles are confined to the inner surface of its atrial appendage. They tend to be fewer and smaller than in the right atrium. This is due to the embryological origin of the auricles, which are the true atria.

Pectinate muscles of the atria are different from the trabeculae carneae, which are found on the inner walls of both ventricles.

The interior of the right atrium has five distinct features:
1. Sinus venarum – smooth, thin-walled posterior part of the right atrium where the SVC, IVC, and coronary sinus open
2. Musculi pectinati – a rough anterior wall of pectinate muscles
3. Tricuspid valve orifice – the opening through which the right atrium empties blood into the right ventricle
4. Crista terminalis – separates the rough (musculi pectinati) from the smooth (sinus venarum) internally
5. Fossa ovalis – a thumbprint size depression in the interatrial septum, which is a remnant of the oval foramen and its valve in the foetus

Carotid endarterectomy is the procedure to relieve an obstruction in the carotid artery by opening the artery at its origin and stripping off the atherosclerotic plaque with the intima. This procedure is performed to prevent further episodes, especially in patients who have suffered ischemic strokes or transient ischemic attacks.

The external carotid artery terminates by dividing into the superficial temporal and maxillary branches. The maxillary artery is the larger of the two terminal branches and arises posterior to the neck of the mandible.

The other arteries mentioned in the answer options branch off from the following:
Temporal arteries from the maxillary artery
Middle meningeal artery from the maxillary artery
Lingual artery from the anterior aspect of the external carotid artery
Facial artery from the anterior aspect of the external carotid artery

Wavelength can be computed as follows:

Wavelength = velocity/frequency

In the given problem, the values stated are:

Frequency = 10 x 10^6
Velocity = 1540 meters per second

Wavelength = 1540/(10×10^6)
Wavelength = 1540/10,000,000 meters
Wavelength = 0.15 millimetres

Heme a exists in cytochrome a and heme c in cytochrome c; they are both involved in the process of oxidative phosphorylation. 5′-Aminolevulinic acid synthase (ALA-S) is the regulated enzyme for heme synthesis in the liver and erythroid cells.

There are two forms of ALA Synthase, ALAS1, and ALAS2.

The minimal alveolar concentration (MAC) is the concentration of an inhalation anaesthetic agent in the lung alveoli required to stop a response to the surgical stimulus in 50% of the patient.

Following factors don’t affect the MAC of the inhaled anaesthetic agents:

Gender, acidosis, alkalosis, hypothyroidism, hyperthyroidism, body weight, serum potassium level, and the duration of the anaesthesia.

MAC increase in children, elevated temperature, high metabolic rate, sympathetic increase and chronic alcoholism.

MAC decrease in low temperature, low oxygen level, old age, hypotension (<40 mmHg), depressant drugs e.g. opioids and low level of catecholamines; alpha methyl dopa. Carbon dioxide O2 at the pressure > 120mmHg is being used in anesthetic-Hinkman as an additive effect to decrease MAC, however, increase concentration of CO2 activates the sympathetic system resulting the MAC increases.

If there is no change in preload and myocardial contractility, there will be decrease in end-diastolic volume and stroke volume. So there must be increase in end-systolic volume.

Oxygen delivery is related to blood flow as most of the oxygen binds to haemoglobin in red blood cells, although a small amount is dissolved in the plasma. Blood flow per 100 g of tissue is greatest in the kidneys.

The following is the oxygen consumption rate of different organs in ml/minute/100g

Hepatoportal = 2.2
Kidney = 6.8
Brain = 3.7
Skin = 0.38
Skeletal muscle = 0.18
Heart = 11

In first order kinetics the rate of elimination is proportional to plasma concentration.

Rate of elimination is described by the following equation:

C = C0. e^-kt

Where:
C=drug concentration,
C0= drug concentration at time zero (extrapolated),
k = rate constant and
t = time.

The initial concentration of this drug is 12 mcg/ml therefore:

The plasma concentration will have halved to 6 mcg/ml at 2 hours.
The plasma concentration will have halved to 3 mcg/ml at 4 hours and
The plasma concentration will have halved to 1.5 mcg/ml t 6 hours.

The trochlear nerve (CN IV) is the fourth and smallest cranial nerve. It’s role is to provide somatic motor innervation of the superior oblique muscle which is responsible for oculomotion.

Injury to the trochlear nerve will result in vertical diplopia, which worsens when looking downwards or inwards. This diplopia presents as an upward deviation of the eye with a head tilt away from the site of the lesion.

The abducens nerve (CN VI) provides somatic motor innervation for the lateral rectus muscle which functions to abduct the eye. Injury to this nerve will cause diplopia and an inability to abduct the eye, causing the patient to have to rotate their head to look sideways.

The facial nerve (CN VII) provides sensory, motor and parasympathetic innervations. It’s motor aspect controls the muscles of facial expression. Damage will cause paralysis of facial expression.

The oculomotor nerve (CN III) provides motor and parasympathetic innervations. Its motor component controls most of the other extraocular muscles. Damage to it will result in ptosis, dilatation of the pupil and a down and out eye position.

The ophthalmic division of the trigeminal nerve (CN VI) is responsible for sensory innervation of skin, mucous membranes and sinuses of the upper face and scalp.

The basilic vein is one of the primary veins that drain the upper limb, like the cephalic vein. It begins as the dorsal venous arch. The basilic vein originates from the ulnar side of the dorsal arch of the upper limb passes along the posteromedial aspect of the forearm, moving towards the anterior surface of the elbow.

The basilic vein pierces the deep fascia at the elbow and joins the venae commitantes of the brachial vein to form the axillary vein.

The basilic vein passes deep under the muscles as it moves midway up the humerus. At the lower border of the teres major muscle, the anterior and posterior circumflex humeral veins feed into it.

The common peroneal (fibular) nerve is a peripheral nerve in the lower limb. It arises of the L4-S2 nerve roots and has sensory and motor innervations:

Sensory: Provides innervation of the lateral leg and foot dorsum.

Motor: Provides innervation of the short head of the biceps femoris, as well as muscles of the anterior and lateral leg compartments.

It is the most commonly damaged nerve in the lower extremity, as it is easily compressed by a plaster cast or injured when the fibula is fractured.

Damage to the common peroneal nerve will result in loss of dorsiflexion at ankle (footdrop, as feet are permanently plantarflexed), with the accompanying high stepping gait.

The saphenous and sural nerve only provide sensory innervation.

The tibial nerve arises from the sciatic nerve (like the common peroneal), but it provides motor innervation to the posterior leg compartments and intrinsic foot muscles. Injury to the tibial nerve will cause loss of plantar flexion, toe flexion and weakened foot inversion.

Extreme hip flexion into the lithotomy or Lloyd-Davies position can result in stretch damage to the neurones (sciatic and obturator nerves) or by applying direct pressure (femoral nerve compression).

The common peroneal (fibular) nerve descends obliquely along the lateral side of the popliteal fossa to the fibular head, medial to biceps femoris.

The sural nerve exits at the fossa’s lower inferolateral aspect and is more at risk in short saphenous vein surgery.

The tibial nerve lies more medially and is even less likely to be injured in this location.

The boundaries of the popliteal fossa are:
Superolateral – the biceps femoris tendon
Superomedial – semimembranosus reinforced by semitendinosus
Inferomedial and inferolateral – medial and lateral heads of gastrocnemius

The contents of the Popliteal fossa are:

1. The popliteal artery
2. The popliteal vein
3. The Tibial nerve and common Fibular nerve
4. Posterior femoral cutaneous nerve: descends and pierces the roof
5. Small saphenous vein
6. popliteal lymph nodes
7. fat

It’s a minute volume divider – True
The Manley MP3 ventilator is classed as a minute volume divider. The entire fresh gas flow or minute volume is delivered to the patient, having been divided into readily set tidal volumes.

Can efficiently ventilate patients with poor pulmonary compliance – False
Ventilating patients with poor pulmonary compliance is not easily achieved, which makes it an unsuitable ventilator for a modern ICU.

Can generate tidal volume up to 1500ml – False
It can generate tidal volumes up to 1000 ml (not 1500 ml), and the inflation pressure can be adjusted by sliding a weight along a rail.

Functions like a Mapleson A system during spontaneous ventilation – False
The ventilator functions like a Mapleson D breathing system (not Mapleson A) during spontaneous ventilation.

Has three sets of bellows – False
The fresh gas flow drives the ventilator which allows rapid detection of gas supply failure. It has two sets of bellows (not three) and three unidirectional valves.

During glycolysis, 2,3-diphosphoglycerate (2,3-DPG) is
created in erythrocytes by the Rapoport-Luebering shunt.

The production of 2,3-DPG increases for several conditions
in the presence of decreased peripheral tissue O2 availability.
Some of these conditions include hypoxaemia, chronic lung
disease anaemia, and congestive heart failure. Thus,
2,3-DPG production is likely an important adaptive mechanism.

High levels of 2,3-DPG cause a shift of the curve to the right.
Low levels of 2,3-DPG cause a shift of the curve to the left,
as seen in states such as septic shock and hypophosphatemia.

Desflurane is a highly fluorinated methyl ethyl ether used for the maintenance of general anaesthesia. It has been identified as a weak triggering anaesthetic of malignant hyperthermia. That, in the absence of succinylcholine, may produce a delayed onset of symptoms.

The operating theatre is an unusual place with several applications of electrical equipment to the human body. This can lead to potential dangers associated with it that need to be prevented. Electrical safety in the operation theatre is the understanding of how these potential dangers can occur and how they can be prevented.

Electricity can cause morbidity or mortality by one of the following ways:
(i) electrocution
(ii) burns
(iii) ignition of a flammable material, causing a fire or explosion.

Electrocution is dependant on factors like duration of contact with electric current, the current pathway and the frequency and size of current.

Option A: The higher the frequency, the less effects of electrocution on the body.

Option B & D: Equipment can be classified in classes and types.
The class designation describes the method used for protection against electrocution. Class I is basic protection, class II is double insulation and class III is safety extra low voltage.
The type designation describes the degree of protection based on the maximum permissible leakage currents under normal and fault conditions.
Type B:
can be class I, II or III but the maximum leakage current must not exceed 100 µA. It is therefore not suitable for direct connection to the heart.
Type BF
Similar to type B, but uses an isolated (or floating) circuit.
Type CF
Only type CF protect against microshock as they allow leakage currents of 0.05 mA per electrode for class I and 0.01 mA for class II. Microshock is a small leakage current that can cause harm because of direct connection to the heart via transvenous lines or wires, bypassing the impedance of the skin, leading to ventricular fibrillation. Microshock current of 100 ?A is sufficient to cause VF.

Option C: A 75mA electrocution can cause ventricular fibrillation. Use the following as a general guide to understand the effect of current size on the body.
1 mA – tingling pain
5 mA – pain
15 mA – tonic muscular contraction
50 mA – respiratory muscle paralysis
75 mA – ventricular fibrillation.

Option E: Wet skin reduces the resistance to current flow and therefore increases the effects of electrocution.

Unionised molecules are more likely than ionised molecules to cross membranes (such as the blood-brain barrier).

Because alfentanil and fentanyl are weak bases, the Henderson-Hasselbalch equation says that the ratio of ionised to unionised molecules is determined by the parent compound’s pKa in relation to physiological pH.

Alfentanil has a pKa of 6.5, while fentanyl has a pKa of 8.4.
At a pH of 7.4, 89 percent of alfentanil is unionised, whereas 9% of fentanyl is.

As a result, alfentanil has a faster onset than fentanyl.

Fentanyl is 83% plasma protein bound
Alfentanil is 90% plasma protein bound.

Alfentanil’s pharmacokinetics are affected by its higher plasma protein binding. Because alfentanil has a low hepatic extraction ratio (0.4), clearance is determined by the degree of protein binding rather than the time it takes to take effect.

The extrinsic pathway is best assessed by the PT time.

D-dimer is a fibrin degradation product which is raised in the presence of blood clots.

A 50:50 mixing study is used to assess if a prolonged PT or aPTT is due to factor deficiency or a factor inhibitor.

The thrombin time is a test used to assess fibrin formation from fibrinogen in plasma. Factors that prolong the thrombin time include heparin, fibrin degradation products, and fibrinogen deficiency.

Intrinsic pathway – Best assessed by APTT. Factors 8,9,11,12 are involved. Prolonged aPTT can be seen in haemophilia and use of heparin.

Extrinsic pathway – Best assessed by Increased PT. Factor 7 involved.

Common pathway – Best assessed by APTT & PT. Factors 2,5,10 involved.

Vitamin K dependent factors are factors 2,7,9,10

Static lung compliance refers to the change in volume within the lung per given change in unit pressure. It is usually measured when air flow is absent, such as during pauses in inhalation and exhalation.

It is a combination of:

Chest wall compliance: normal value is 200 mL/cmH2O
Lung tissue compliance: normal value is 200 mL/ cmH2O

It is represented mathematically as:

1/Crs = 1/Cl + 1/Ccw

Where,

Crs = total compliance of the respiratory system
Cl = compliance of the lung
Ccw = compliance of the chest wall

Therefore in this case:

1/Crs = 1/200 + 1/200

1/Crs = 0.005 + 0.005 = 0.01

1/Ct = 0.01

Rearranging equation gives:

Ct = 1/0.01 = 100 mL/cmH2O.

Bernoulli’s principle states that as the speed of a moving fluid increases, there is a simultaneously decrease in static pressure or a decrease in the fluid’s potential energy.
This is seen in the simultaneous increase in speed and kinetic energy and fall in pressure that causes entrainment of large volumes of air into a flow of 100% oxygen in the nozzle of HAFOE masks.

The reduction in fluid pressure that happens when a fluid flows through a constriction in a tube is the Venturi effect.

When a flow of gas or liquid attaches itself to a nearby surface and remains attached even when the surface curves away from the initial direction of flow, this is the Coanda effect.

The branch of engineering and technology that is concerned with the building of devices that use the flow and pressure of a fluid for functions usually performed by electronic devices is Fluidics . Fluidic logic is used to power some ventilators.

The branch of engineering that utilises pressurised gases is Pneumatics.

Medical gas cylinders are made up of molybdenum steel but not cast iron. They are checked and assessed at a regular interval.

At least one cylinder in each hundred are tested for tensile, pressure, smash, twist and straightening.

Nitrous Oxide cylinders contain a mixture of liquid and vapour at a pressure of approx. 4500 kPa or 45 Bar. Carbon dioxide cylinder contain gas at the pressure of 5000kPa.

The filling ratio is the ratio of mass of liquified gas in the cylinder to the mass of water required to fill the cylinder at the temperature of 15ºC. In the united kingdom, filling ratio of liquid nitrous oxide is 0.75. The cylinders are usually attached to the anaesthetic machine. As nitrous oxide is an N-methyl-d-aspartate receptor antagonist that may reduce the incidence of chronic post-surgical pain.

Phase 0 trials assist the scientists in studying the behaviour of drugs in humans by micro dosing patients. They are used to speed up the developmental process. They have no measurable therapeutic effect and efficiency.

Phase 1 is associated with assessing whether a drug is safe to use or not. The process is extensive and can take up to several months. It also involves healthy participants (less than 100) that are paid to take part in the study. The side effects upon increasing dosage are also addressed by the study. The effects the drug has on humans including how its absorbed, metabolized and excreted are studied. Approximately 70% of the drugs pass this phase.

Phase 2 trials involve patients that are suffering from the disease under study and are associated with determining the efficiency and the optimum dosage of the drug.

Phase 3 also assesses the efficacy but at a higher scale with larger population sample.

Phase 4 trials are involved with the long term effects and side effects of the drug.

Glycolysis occurs in the cytoplasm of the cell. It converts 1 glucose molecule (6-carbon) to pyruvate (two 3-carbon molecules) and produces 4 ATP molecules and 2NADH but uses 2 ATP in the process with an overall net energy production of 2 ATP.

Pyruvate is then oxidised to acetyl coenzyme A (generating 2 NADH per pyruvate molecule). This takes place in the mitochondria and then enters the Krebs cycle (citric acid cycle). It produces 2 ATP, 8 NADH and 2 FADH2 per glucose molecule.

Electron transport phosphorylation takes place in the mitochondria. The aim of this process is to break down NADH and FADH2 and also to pump H+ into the outer compartment of the mitochondria. It produces 32 ATP with an overall net production of 36ATP.

In anaerobic respiration which occurs in the cytoplasm, pyruvate is reduced to NAD producing 2 ATP.

The ventilatory anaerobic threshold (VAT), formerly referred to as the anaerobic threshold, is an index used to estimate exercise capacity. During the initial (aerobic) phase of CPET, which lasts until 50–60% of Vo2max is reached, expired ventilation (VE) increases linearly with Vo2 and reflects aerobically produced CO2 in the muscles. Blood lactate levels do not change substantially during this phase, since muscle lactic acid production is minimal.

During the latter half of exercise, anaerobic metabolism occurs because oxygen supply cannot keep up with the increasing metabolic requirements of exercising muscles. At this time, there is a significant increase in lactic acid production in the muscles and in the blood lactate concentration. The Vo2 at the onset of blood lactate accumulation is called the lactate threshold or the VAT. The VAT is also defined as the point at which minute ventilation increases disproportionately relative to Vo2, a response that is generally seen at 60–70% of Vo2max.

The VAT is a useful measure as work below this level encompasses most daily living activities. The ability to achieve the VAT can help distinguish cardiac and non‐cardiac (pulmonary or musculoskeletal) causes of exercise limitation, since patients who fatigue before reaching VAT are likely to have a non‐cardiac problem.

When VAT is detected, patients with PVo2 of ⩽10 ml/kg/min have a high event rate.

Cardiac conduction

Phase 0 – Rapid depolarization. Opening of fast sodium channels with large influx of sodium

Phase 1 – Rapid partial depolarization. Opening of potassium channels and efflux of potassium ions. Sodium channels close and influx of sodium ions stop

Phase 2 – Plateau phase with large influx of calcium ions. Offsets action of potassium channels. The absolute refractory period

Phase 3 – Repolarization due to potassium efflux after calcium channels close. Relative refractory period

Phase 4 – Repolarization continues as sodium/potassium pump restores the ionic gradient by pumping out 3 sodium ions in exchange for 2 potassium ions coming into the cell. Relative refractory period

The tibial nerve lies on top of the vessels contained within the inferior aspect of the popliteal fossa.

In the superior aspect of the fossa, the tibial nerve runs lateral to the vessels, before then travelling superficial to the vessels, and then finally changing course to lie medial to the vessels.

The popliteal artery is the most deep structure present in the popliteal fossa

The ideal volatile agent for a day case surgery inhalational induction should have the following characteristics:

It has a pleasant scent that is not overpowering.
Breathing difficulties, coughing, or laryngeal spasm are not caused by this substance.
The action has a quick onset and a quick reversal.

The blood:gas partition coefficient is a physicochemical property of a volatile agent that determines the onset and offset of anaesthesia. The greater an agent’s insolubility in plasma, the faster its alveolar concentration rises.

The blood gas partition coefficients of the most commonly used volatile anaesthetic agents are as follows:
Halothane 2.3
Desflurane 0.45
Sevoflurane 0.6
Nitrous oxide 0.47
Isoflurane 1.4

Although halothane has a pleasant odour, it has a slower offset than sevoflurane.

Sevoflurane also has a pleasant odour and is less likely than desflurane to cause airway irritation and breath-holding.

The choice of agent for inhalational induction is unaffected by potency/lipid solubility measures such as the oil: gas partition coefficient and MAC.

In this case, an agent’s saturated vapour pressure is irrelevant.

An echocardiogram provides real-time visualisation of cardiac structures. The ejection fraction (EF) is normally measured using this system.

The ejection fraction (EF) can be deduced mathematically if the patient’s end-diastolic volume (EDV), end-systolic volume (ESV) and stroke volume (SV) are known, as:

SV = EDV – ESV, and

EF = SV/EDV x 100

The normal range for EF is >55-70%.

For this patient,

SV= 40 – 30 = 10 mL, therefore

EF = 10/40 x 100 = 25%

Nitric oxide (NO), an endothelial-derived relaxant factor (EDRF), is a powerful vasodilator. Its cell-signalling molecule is calcium-dependant and generated endogenous by nitric oxide synthetases from the precursor L-arginine, oxygen and NADPH. Three main isoforms have been isolated and they are inducible (iNO), neuronal (nNO) and endothelial (eNO).

Endothelial NO stimulates intracellular guanylyl cyclase which generates cyclic GMP (cGMP) from its action on guanylyl tri-phosphate (GTP). The cGMP goes on to activate protein kinase G (PKG). PKG phosphorylates cell membrane proteins that regulate intracellular calcium concentrations and level of calcium sensitisation.

Smooth muscle vasodilatation results from:

1. Light chain phosphatase activation.
2. Inhibition of calcium entry into the cell (reducing Ca2+ concentrations) and
3. Hyperpolarisation of cells by activation of H+ channels.

The internal laryngeal nerve provides sensory innervation to the laryngeal mucosa, and injury to it will cause loss of sensation.

The internal laryngeal nerve lies inferior to the piriform recess mucous membrane, placing it at high risk of irritation or damage by objects which become lodged in the recess.

The internal laryngeal artery branches off the superior laryngeal artery accompanied by the superior laryngeal nerve, inferior to the thyroid artery which branches off the superior thyroid artery close to its bifurcation from the external carotid artery.

Carbon dioxide absorbs the most infrared (IR) light between the wavelengths of 4.2-4.4m (4.26m is ideal).

Nitrous oxide absorbs infrared light at wavelengths of 4.4-4.6m (very similar to CO2) and less so at 3.9m.

At a frequency of 4.7m, carbon monoxide absorbs the most IR light.

At 3.3 m and throughout the ranges 8-12 m, the volatile agents have strong absorption bands.

Although oxygen does not absorb infrared light, it collides with CO2 molecules, interfering with absorption. The absorption band is widened as a result of this (so called collision or pressure broadening). A drop of 0.5 percent in measured CO2 can be caused by 95% oxygen.

Nitrous oxide causes a greater inaccuracy of 0.1 percent per ten percent of nitrous oxide.

Water vapour absorbs infrared light as well, resulting in absorption band overlap, collision broadening, and partial pressure dilution. Water traps and water permeable tubing are used to reduce inaccuracies.

Collision broadening is compensated for in modern gas multi-gas analysers.

Ambient pressure has no effect on a volatile agent’s saturated vapour pressure (SVP). At a temperature of 20°C, the SVP of sevoflurane is approximately 21 kPa, or 21% of atmospheric pressure (100 kPa).

The SVP of sevoflurane remains the same when the ambient pressure is doubled to 200 kPa, but the output of the vaporiser is halved, now 21 percent of 200 kPa, equalling 10.5 percent. The vaporiser’s output has increased to 1%, but the partial pressure output has remained unchanged. The splitting ratio will not change because it is determined by temperature changes.

Calculations can be made as follows:

Vaporizer output % (ambient pressure) = % volatile (calibrated) x 100 kPa calibrated pressure/ambient pressure
2% = 2% (dialled) × 100/100
2% of 100 = 2 kPa

Altitude, pressure 50 kPa
4% = 2% (dialled) × 100/50
4% of 50 = 2 kPa

High pressure at 200 kPa
1% = 2% (dialled) × 100/200
1% of 200 = 2 kPa

Sevoflurane has a boiling point of 58°C and, unlike desflurane (which has a boiling point of 22.8°C), does not need to be heated and pressurised with a Tec 6 vaporiser.

Work up bias involves comparing the novel diagnostic test with the current standard test. A portion of the patients undergo the standard test while others undergo the new test as the standard test is costly. The result can be alteration in specify and sensitivity.

Selection bias is when randomisation is not achieved.

Attention bias refers to the person’s failure to consider various alternatives when he pre occupied by some other thoughts.

Instrument bias is related to the experience and extent of familiarization of the participating individuals with the test.

Co intervention bias is characterized by the groups receiving different co interventions.

During analytical stage a technique called stratification is used for controlling confounding variables. This technique involves sorting out the data into discernible groups.

Osmolarity refers to the osmotic pressure generated by the dissolved solute molecules in 1 L of solvent. Measurements of osmolarity are temperature dependent because the volume of the solvent varies with temperature. The higher the osmolarity of a solution, the more it attracts water from an opposite compartment.

Osmolarity can be computed using the following formulas:

Osmolarity = Concentration x number of dissociable particles; OR
Plasma osmolarity (Posm) = 2([Na+]) + (glucose in mmol/L) + (BUN in mmol/L)

Posm = 2 (144) + 3.5 + 9.5 = 301 mOsm/L

Suppose there is electrical neutrality, the formula will double the cation activity to account for the anions.

Plasma osmolarity (Posm) = 2([Na+] + [K+]) + (glucose in mmol/L) + (BUN in mmol/L)

Posm = 2 (144 + 6) + 3.5 + 9.5 = 313 mOsm/L

The fibrotendinous ring formed by the congregation of the rectus muscles at the apex of the orbit does not include superior oblique. This muscle is completely outside the ring and so it is the most difficult muscle to anaesthetise completely. A good grasp of the anatomy of the area being anaesthetised is important with all regional anaesthetic techniques so that potential problems and complications with a block can be anticipated.

The borders of this pyramid whose apex points upwards and outwards of the bony orbit are as follows:
Floor – Zygoma and Maxilla
Roof – frontal bone
Medial wall – maxilla, ethmoid, sphenoid and lacrimal bones.
Lateral wall – greater wing of the sphenoid and the zygoma.

The four recti muscles (superior, medial, lateral and inferior) originate from a tendinous ring (the annulus of Zinn) and extend anteriorly to insert beyond the equator of the globe. Bands of connective tissue are present between the rectus muscles forming a conical structure and hinder the passage of local anaesthetic.

The superior oblique muscle is situated outside this ring and is the most difficult muscle to anaesthetise completely, particularly with a single inferotemporal peribulbar injection. An additional medial injection may help to prevent this.

The cranial nerve supply to the extraocular muscles are:
3rd (inferior oblique, inferior recti, medial and superior)
4th (superior oblique), and
6th (lateral rectus).

The long and short ciliary nerves provide the sensory supply to the globe and these are branches of the nasociliary nerve, (which is itself a branch of the ophthalmic division of the trigeminal nerve).

To achieve anaesthesia for the eye, these nerves which enter the fibrotendinous ring need to be fully blocked to anaesthetise the eye for surgery.

Sodium-chloride symporter inhibitor.

The thiazide sensitive sodium chloride symporter is inhibited by thiazides at the proximal portion of the distal convoluted tubule leading to increased sodium and water excretion. Increased delivery of sodium to the distal portion of the distal convoluted tubule promotes potassium loss. This is why thiazides are associated with hyponatraemia and hypokalaemia.

Carbonic anhydrase inhibitors are used mainly in the treatment of glaucoma. They act on the proximal convoluted tubule to promote bicarbonate, sodium and potassium loss.

Sodium potassium chloride symporter is inhibited by Loop diuretics.
Epithelial sodium channels are inhibited by Amiloride.
Drugs which lead to nephrogenic diabetes insipidus such as lithium and demeclocycline, are Inhibitors of vasopressin.

The superior thyroid artery is the first branch of the external carotid artery. The other branches of the external carotid artery are:
1. Superior thyroid artery
2. Ascending pharyngeal artery
3. Lingual artery
4. Facial artery
5. Occipital artery
6. Posterior auricular artery
7. Maxillary artery
8. Superficial temporal artery

The inferior thyroid artery is derived from the thyrocervical trunk.

The wall of an artery has three layers: (innermost to outermost)
1. Tunica intima – in direct contact with the blood inside the vessel and contains endothelial cells separated by gap junctions.
2. Tunica media – contains smooth muscle cells and is separated from the intima by the internal elastic lamina and the adventitia by the external elastic lamina.
3. Tunica adventitia – contains the vasa vasorum, fibroblast, and collagen.

Aortic dissection is when a tear arises in the innermost layer of the aorta and penetrates through the tear, entering the media layer. The inner and middle layers of the aorta split (dissect).

The arteries of the midgut (superior mesenteric artery) and hindgut (inferior mesenteric artery) give off terminal branches that form an anastomotic vessel called the marginal artery of Drummond. It runs in the inner margins of the colon and gives off short terminal branches to the bowel wall.

The marginal artery is formed by the main branches and arcades arising from the ileocolic, right colic, middle colic, and left colic arteries. It is most apparent in the ascending, transverse, and descending colons and poorly developed in the sigmoid colon.

Noradrenaline also called norepinephrine belongs to the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter.

They have sympathomimetic effects acting via adrenoceptors (?1, ?2,?1, ?2, ?3) or dopamine receptors (D1, D2).

May cause reflex bradycardia, reduce cardiac output and increase myocardial oxygen consumption

Correctly used, antibiotic prophylaxis can reduce
the total use of antibiotics.
There is strong scientific support that antibiotic
prophylaxis reduces the development of infection after:

• Operations and endoscopic procedures in the large intestine,
  the rectum, and the stomach (including appendectomies and
  penetrating abdominal trauma), and after percutaneous endoscopic gastrostomy (PEG)
• Cardiovascular surgery, and insertion of pacemakers
• Breast cancer surgery
• Hysterectomy
• Reduction of simple fractures and prosthetic limb surgery
• Complicated surgery for cancer in the ear, nose, and throat
  regions
• Transrectal biopsy and resection of the prostate (febrile urinary
  tract infection and blood poisoning).

In most cases the scientific evidence is inadequate to determine
which type of antibiotic is most effective for antibiotic prophylaxis.

There are 4 different types of globin chains which surround 4 heme molecules in haemoglobin (Hb) – α (alpha), β (beta), γ (gamma), and δ (delta)
α chains are essential.
δ2β2 and β2γ2 are not found in a healthy adult.
97% of the Hb in a healthy adult is made of α2β2 (2 α chains and 2 β chains).
α2δ2 accounts for around 1.5-3% of the adult Hb.
α2γ2 accounts for less than 1%.

With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.

Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain. There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions. The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.

The area described in the question is supplied by the intercostobrachial nerve, which provides sensory innervation to the portions of the axilla, tail of the breast, lateral chest wall and medial side of the arm.

It is a common for it to be ‘missed’ during administration of local anaesthesia because of its very superficial anatomic course. It may be anesthetized by giving an analgesia from the upper border of the biceps at the anterior axillary fold, to the margin of the triceps by the axillary floor.

Laminar flow can be defined as the motion of a fluid where every particle in the fluid follows the same path of its previous particles. The following are properties of laminar flow of gas or fluids:

1. Smooth unobstructed flow of gas through a tube of relatively uniform diameter
2. Few directional changes
3. Slow, steady flow through straight smooth, rigid, large calibre, cylindrical tube
4. Outer layer flow slower than the centre due to friction, results in discrete cylindrical layers, or streamlines
5. Double flow by doubling pressure as long as the flow pattern remains laminar

Poiseuille’s Law relates the factors that determine laminar flow. It indicates the degree of resistance to fluid flow through a tube. The resistance to fluid flow through a tube is directly related to the length, flow and viscosity; and inversely related to the radius of the tube to the fourth power. This means that, when the radius is doubled, there is increase in flow by a factor of 16.

The usual method of calculating the dose of a drug to be given to patients of normal weight is to use total body weight (TBW). This is because the lean body weight (LBW) and ideal body weight (IBW) dosing scalars are similar in these patients.

Because the LBW and fat mass do not increase in proportion in patients with morbid obesity, this is not the case. Drugs that are lipid soluble, such as propofol or thiopentone, can cause a relative overdose. Lean body mass is a better scalar in these situations.

Suxamethonium has a small volume of distribution, so the dose is best calculated using the TBW to ensure optimal and deep intubating conditions. The higher dose was justified because these patients’ plasma cholinesterase activity was elevated.

Other scalars include:

The dose of highly lipid soluble drugs like benzodiazepines, thiopentone, and propofol can be calculated using lean body weight (LBW). The formula LBW = IBW + 20% can be used on occasion.

Fentanyl, rocuronium, atracurium, vecuronium, morphine, paracetamol, bupivacaine, and lidocaine are all administered with LBW.

Formulas can be used to calculate the ideal body weight (IBW). There are a number of drawbacks, including the fact that patients of the same height receive the same dose, and the formulae do not account for changes in body composition associated with obesity. Because IBW is typically lower than LBW, administering a drug based on IBW may result in underdosing. The body mass index (BMI) isn’t used to calculate drug dosage directly.

The oxygen consumption rate (VO2) at rest is 3.5 ml/kg/minute (one metabolic equivalent or 1 MET).
3.86 ml/kg/minute thyrotoxicosis

Young children consume a lot of oxygen: around 7 ml/kg/min when they are born. The metabolic cost of breathing is higher in children than in adults, and it can account for up to 15% of total oxygen consumption. Similarly, an infant’s metabolic rate is nearly twice that of an adult, resulting in a larger alveolar minute volume and a lower FRC.

At term, oxygen consumption at rest can increase by as much as 40% (5 ml/kg/minute) and can rise to 60% during labour.

When compared to normal basal metabolism, sepsis syndrome increases VO2 and resting metabolic rate by 30% (4.55 ml/kg/minute). In septicaemic shock, VO2 decreases.

Dobutamine hydrochloride was infused into 12 healthy male volunteers at a rate of 2 micrograms per minute per kilogramme, gradually increasing to 4 and 6 micrograms per minute per kilogramme. Dobutamine was infused for 20 minutes for each dose. VO2 increased by 10% to 15%. (3.85-4.0 ml/kg/min).

Linear regression, using a technique called curve fitting, allows us to make predictions regarding a certain variable.

Correlation coefficient gives us an idea whether or not the two parameters provide have any relation of some sort or not i.e. does change in one prompt any change in other?

Standard error can be calculated by the following formula:
Standard Error= (Standard Deviation)/√(Sample Size)
= (16) / √(100)
= 16 / 10
= 1.6

Patients who present for surgery may be on prescription medication or natural/herbal therapies. These have relevance for anaesthesia since they can cause drug interactions.

Ephedra (Ma Huang) is a drug derived from the plant Ephedra sinica that is used as a CNS stimulant, weight reduction aid, and asthma therapy. It is a combination of alkaloids that includes ephedrine which stimulates noradrenaline release from pre-synaptic neurones by acting directly on alpha and beta adrenoreceptors. The use of sympathomimetic drugs together can cause cardiovascular instability.

Ginkgo Biloba contains anti-oxidant characteristics and is used to treat Alzheimer’s disease, vascular dementia, and peripheral vascular disease. It lowers platelet adhesiveness and raises the risk of bleeding by decreasing platelet activating factor (PAF), especially in individuals who are also taking anticoagulants and antiplatelet drugs.

The extract from St. John’s Wort is utilised as an antidepressant because it is a cytochrome P450 isoenzyme inhibitor as well as a serotonin uptake inhibitor. When drugs like fentanyl or tramadol are used during an anaesthetic, there is a risk of serotonin syndrome developing.

The root of a pepper is used to make kava (Piper methysticum). It is a weak GABAA agonist which has the potential to augment the effects of propofol and benzodiazepines, which are volatile anaesthetics.

Garlic is made from the allium sativum plant and is used to treat hypertension and hyperlipidaemia. It includes cysteine, which inhibits platelet aggregation irreversibly, amplifying the effects of aspirin and NSAIDs.

Echinacea is a common herbal medicine that stimulates the immune system by modulating cytokine signalling. In individuals who require organ transplantation, it should be avoided.

Cardiac conduction

Phase 0 – Rapid depolarization. Opening of fast sodium channels with large influx of sodium

Phase 1 – Rapid partial depolarization. Opening of potassium channels and efflux of potassium ions. Sodium channels close and influx of sodium ions stop

Phase 2 – Plateau phase with large influx of calcium ions. Offsets action of potassium channels. The absolute refractory period

Phase 3 – Repolarization due to potassium efflux after calcium channels close. Relative refractory period

Phase 4 – Repolarization continues as sodium/potassium pump restores the ionic gradient by pumping out 3 sodium ions in exchange for 2 potassium ions coming into the cell. Relative refractory period

The following terms are used in medical testing:

True negative – The test is negative and the patient does not have the disease.
True positive – The test is positive and the patient has the disease.
False positive – The test is positive but the patient does not have the disease.
False negative – The test is negative but the patient has the disease.

The sensitivity of a predictive test = true positives / (true positives + false negatives).

The specificity of a test = true negatives / (false positives + true negatives).

The negative predictive value of a test = true negatives / (false negatives + true negatives).

The extrinsic pathway is considered as the main pathway of coagulation cascade.

Heparin is known to inhibit the activation of coagulation factors 2,9,10, and 11.

The extrinsic and intrinsic pathways meet at the activation of coagulation factor 10.

Fibrinogen is converted into Fibrin in the presence of Thrombin. Plasminogen is converted into plasmin during fibrinolysis to breakdown fibrin clot.

Ptosis and mydriasis are visible in surgical third nerve palsy, and the eye looks ‘down and out.’ The loss of innervation to all of the major structures supplied by the oculomotor nerve is reflected in these characteristics.

Ptosis is caused by the paralysis of the levator palpebrae superioris in oculomotor nerve palsy. Due to the unopposed actions of the superior oblique and lateral rectus muscles, the eye rotates down and out.

Mydriasis is caused by surgical (compressive) causes of third nerve palsy, which disrupt the parasympathetic pupillomotor fibres on the nerve’s periphery.

Medical (ischaemic) causes of a third nerve palsy, on the other hand, leave the superficial parasympathetic fibres relatively unaffected and the pupil unaffected.

Horner’s syndrome is characterised by ptosis, anhidrosis, and miosis, which are caused by a loss of sympathetic innervation to the tarsal muscle of the upper lid, facial skin, and dilator pupillae, respectively.

Funnel plot is essentially a scatterplot of the effect of treatment against a particular measure of study precision. Its primal purpose is to serve as a visual aid and help in detection of bias or systematic heterogenity.

At rest, the heart has the greatest a-vO2 difference, a high capillary to myocyte ratio, short diffusion distances, and a high mitochondrial density. The flow of blood through the coronary arteries is also tightly controlled. At rest, 70-80 percent of the oxygen available to the cardiac muscle is extracted, increasing to 90 percent during exercise.

The a-vO2 difference indicates the body’s or an individual organ’s ability to extract oxygen from the blood.

CaO2 is influenced by a number of factors, including Hb concentration, PaO2 and pulmonary diffusion capacity.

CvO2 is influenced by a number of factors, including capillary density, regional blood flow, heart, resting skeletal muscle, kidney, intestine and skin.

Glutamic acid decarboxylase is responsible for the catalyses of glutamate to gamma-aminobutyric acid (GABA)

Catechol-o-methyl transferase catalyses the degradation and inactivation of dopamine into 3-methoxytyramine, epinephrine into metanephrine, and norepinephrine into normetanephrine and vanylmethylmandelic acid (VMA).

Monoamine oxidase catalyses the oxidation of norepinephrine to vanylmethylmandelic acid (VMA) and serotonin to 5-hydeoxyindole acetic acid (5-HIAA).

Cholinesterase functions to catalyse the split of acetylcholine into choline and acetic acid.

Campylobacter is the commonest bacterial cause of infectious intestinal disease in the UK. The majority of cases are caused by the Gram-negative bacillus Campylobacter jejuni which is spread by the faecal-oral route. The incubation period is 1-6 days.

Features include a prodrome phase with headaches and malaise, then diarrhoea occurs which is often bloody.
There is often abdominal pain which may mimic appendicitis.

It is usually self-limiting but treatment is warranted if the infection is severe or the infection occurs in an immunocompromised patient.
Severe infection comprises of high fever, bloody diarrhoea, or more than eight stools per day or symptoms last for more than one week.
This management would include antibiotics and the first-line antibiotic is clarithromycin.
Ciprofloxacin is an alternative but there are strains with decreased sensitivity to ciprofloxacin which can be frequently isolated.

Complications include:
1.Guillain-Barre syndrome may follow Campylobacter
2. Jejuniinfections
3. Reactive arthritis
4. Septicaemia, endocarditis, arthritis

The commonest and most likely cause of a gradual rise in end-tidal CO2 (EtCO2) occurring during anaesthesia in a spontaneously breathing patient is hypoventilation. This occurs from the respiratory depressant effects of the opioid and sevoflurane.

Malignant hyperthermia should be sought if the EtCO2 shows further progressive rise.

Causes of rebreathing and a rise in the baseline of the capnograph can be caused by exhausted soda lime and inadequate fresh gas flow into the Bain circuit.

A sudden rise in EtCO2 can be caused deflation of the tourniquet.

Maintenance therapy aims to replace water and electrolytes lost under ordinary conditions. In the perioperative period, maintenance fluid administration may not sufficiently account for the increased fluid requirements caused by third-space losses into the interstitium and gut. Specific recommendations vary with the patient, the procedure, and the type and amount of fluid administered during the operation. The fluid for maintenance therapy replaces deficits arising primarily from insensible losses and urinary or gastrointestinal (GI) losses.

The maintenance fluid volume can be computed using the Holliday-Segar method.

Body weight Fluid volume
first 10 kg 4 ml/kg/hr
next 10-20 kg 2 ml/kg/hr
>20 kg 1 ml/kg/hr

In the past few years, there has been growing recognition of the increased risk of hyponatremia in hospitalized children in intensive care and postoperative settings who receive hypotonic maintenance fluids. Several studies, including a randomized controlled trial and a Cochrane analysis, found that the use of isotonic fluids is associated with fewer electrolyte derangements and concluded that isotonic maintenance fluids are preferable to hypotonic solutions in hospitalized children.

A European consensus statement suggests that an intraoperative fluid should have an osmolarity close to the physiologic range in children in order to avoid hyponatremia, an addition of 1-2.5% in order to avoid hypoglycaemia, lipolysis or hyperglycaemia and should also include metabolic anions as bicarbonate precursors to prevent hyperchloremic acidosis.

A rate of 40 ml/hr is suboptimal.

If 0.9% NaCl with 0% glucose is given at a rate of 65 ml/hr, despite of the correct infusion rate, large volumes can lead to hyperchloremic acidosis.

If 0.18% NaCl with 4% glucose is given at a rate of 65 ml/hr, infusion of this fluid regimen can lead to hyponatremia because of its hypotonicity.

The first line of defence against acid-base disorder is buffering. The blood mainly utilizes bicarbonate ion (HCO3-) for its buffering capacity (total of 53%, plasma and red blood cells combined).

Strong acids, when acted upon by a buffer, release H+, which then combines to HCO3- and forms carbonic acid (H2CO3). When acted upon by the enzyme carbonic anhydrase, H2CO3 dissociates into H2O and CO.

The rest are the percentage of utilization for the following buffers:
Haemoglobin (by RBCs) – 35%
Plasma proteins (by plasma) – 7%
Organic phosphates (by RBCs) – 3%
Inorganic phosphates (by plasma) – 2%

The external carotid artery has eight important branches:
Anterior surface:
1. Superior thyroid artery (first branch)
2. Lingual artery
3. Facial artery
Medial branch
4. Ascending pharyngeal artery
Posterior branches
5. Occipital artery
6. Posterior auricular artery
Terminal branches
7. Maxillary artery
8. Superficial temporal artery

The external carotid has eight branches, 3 from its anterior surface ; thyroid, lingual and facial. The pharyngeal artery is a medial branch. The posterior auricular and occipital are posterior branches.

BMR is lower in females than males.

It decreases with increasing age.

There is an increase in BMR with increased muscle (i.e. lean tissue)

BMR is increased in stress and illness. There is also an catabolic state in these conditions.

Atypical antipsychotic drugs include risperidone and quetiapine. They not only inhibit dopamine receptors in the limbic system, but also histamine (H1) and alpha2 adrenoreceptors. When combined with general and/or central neuraxial block, this might result in severe hypotension.

Donepezil (Aricept) is an acetylcholinesterase (AChE) inhibitor that increases the neurotransmitter acetylcholine in the cerebral cortex and hippocampus in a reversible, non-competitive manner. It is used to reduce the advancement of Alzheimer’s disease symptoms (AD). Rivastigmine and galantamine are two more drugs that work in the same way.

Ginkgo Biloba contains anti-oxidant characteristics and is used to treat early-stage Alzheimer’s disease, vascular dementia, and peripheral vascular disease. It lowers platelet adhesiveness and decreases platelet activating factor (PAF) increasing the risk f bleeding, especially in individuals who are also taking anticoagulants and antiplatelet medication.

Memantine is an antagonist of the NMDA receptor. Synaptic plasticity, which is thought to be a critical component of learning and memory, can be inhibited at high doses. The use of ketamine is a relative contraindication since antagonism of this receptor can cause a dissociative state.

The cylindrical structure(spine), starts from the foramen magnum in medulla oblongata at the skull’s base. Its length varies in gender with men having 45cm and women having up to 43 cm. The spine contains 31 pairs of spinal nerves, named according to the spinal region:
– 8 cervical nerve pairs ( C1-C8)
– 12 thoracic nerve pairs ( T1-T12)
– 5 lumbar nerve pairs (L1-L5)
– 5 sacral nerves (S1-S5) and
– 1 coccygeal nerve pair.
These spinal nerves are classified as the peripheral nervous system though they branch from the spinal cord and central nervous system. They interact directly with the spinal cord to modulate the motor and sensory information from the peripheral’s region. As the nerves emerges form the spinal cords they are known as rootlets. They join to form nerve roots, and depending on their position, we have anterior nerve roots and posterior.

The spinal cord is supplied by two posterior and one anterior spinal arteries which anastomoses caudally, at the conus medullaris.

The anterior spinal artery supplies the anterior two-thirds of the spinal cord and medulla. Disruption of the anterior spinal artery supply is characterised by ischaemia or infarction of motor tracts (corticospinal) and loss of pain and temperature sensation below the level of the lesion.

The posterior spinal arteries supply the posterior columns (posterior third of the spinal cord). Infarction of the posterior columns results in the loss of proprioceptive, vibration and two-point discrimination.

The spinal cord normally ends at the level of L1 or L2 in an adult and L3 in a newborn.

Body fluid compartments in a 70kg male:
Total volume=42L (60% body weight)
Intracellular fluid compartment (ICF) =28L
Extracellular fluid compartment (ECF) = 14L

ECF comprises:
Intravascular fluid (plasma) = 3L
Extravascular fluid = 11L

Extravascular fluids comprises:
Interstitial fluid = 10.5L
Transcellular fluid = 0.5L

Bucks fascia refers to the layer of loose connective tissue, nerves and blood vessels that encapsulates the penile erectile bodies, the corpa cavernosa and the anterior part of the urethra, including the entirety of the spongiose part of the urethra.

It runs with the external spermatic fascia and the penile suspensory ligament.

The inguinal triangle of Hesselbach is an important clinical landmark on the posterior wall of the inguinal canal. It has the following relations:
Inferiorly – medial third of the inguinal ligament
Medially – lower lateral border of the rectus abdominis
Laterally – inferior epigastric vessels

Direct inguinal hernia is when the bowel bulges directly through the abdominal wall. These hernias usually protrude through Hesselbach’s triangle

The surface marking for locating the femoral artery is the mid-inguinal point, which is the halfway point between the anterior superior iliac spine (ASIS) and the pubic symphysis.

The other mentioned options are not specific for any landmark.

However, it is important to note the difference between the mid inguinal point and the midpoint of the inguinal ligament, which is travels from the ASIS to the pubic tubercle.

When the association among any two classes of object is defined by the presence of a third entity it is termed as indirect association. For an instance, the age of the employee may affect the rate of pay, which would have implications on job satisfaction. So, in this example, an indirect relationship between age and job satisfaction exists due to a third party i.e. rate of pay.

Small measurement units are denoted by the following SI mathematical prefixes:

1 deci = 0.1
1 milli = 0.001
1 micro = 0.000001
1 nano = 0.000000001
1 pico = 0.000000000001
1 femto = 0.000000000000001 (used to measure red blood cell volume)
1 atto = 0.000000000000000001

The most likely of the differential diagnosis in this case is a duodenal ulcer located on the posterior abdominal wall.

These can cause an erosion of the abdominal wall, eventually affecting the gastroduodenal artery and resulting in major bleeding and haematemesis.

Gastroduodenal artery supplies the pylorus, proximal part of the duodenum, and indirectly to the pancreatic head (via the anterior and posterior superior pancreaticoduodenal arteries)

When the convulsion lasts for five or more than five minutes, or if there are recurrent episodes of convulsions in a 5 minute period without returning to the baseline, it is termed as Status Epilepticus.
The first priority in the patient with seizures is maintaining the airway, breathing, and circulation.

Guideline for the management of Status Epilepticus in children by Advanced Life Support Group is as follow:

Step 1 (Five minutes after the start of seizures):

If intravascular access is available start treatment with lorazepam 0.1 mg/kg IV
If no intravascular access then give buccal midazolam 0.5 mg/kg or rectal diazepam 0.5 mg/kg.

Step 2 (Ten minutes after the start of seizure):

If the convulsions continue then a second dose of benzodiazepine should be given. Senior should be called on-site and phenytoin should be prepared.
No more than two doses or benzodiazepines should be given (including any doses given before arrival at the hospital)
If still no IV access then obtain intraosseous access (IO).

Step 3 (Ten minutes after step 2)

Senior help along with anaesthetic/ICU help should be sought
Phenytoin 20 mg/kg IV over 20 minutes
If the seizure stops before the full dose of phenytoin is given then the infusion should be completed as this provides up to 24 hours of anticonvulsant effect
In children already receiving phenytoin as treatment for epilepsy then an alternative is phenobarbitone 20 mg/kg IV over five minutes
Once the phenytoin is started, senior staff may wish to give rectal paraldehyde 0.4 mg/kg although this is no longer included in the routine algorithm recommended by APLS.

Step 4 (20 minutes after step 3)

If 20 minutes after starting phenytoin the child remains in status epilepticus then rapid sequence induction of anaesthesia with thiopentone and a short acting paralysing agent is needed and the child transferred to paediatric intensive care.

An epidemic is declared when the increase in a give disease is above a certain level in a specific interval of time.

An endemic is the general, usual level of a disease in a population at a particular time.

A pandemic is an epidemic that is spread across many countries and continents.

An intra-operative air embolism occurs when air becomes trapped in the blood vessels during surgery.

A transoesophageal echocardiography (OE) uses invasive echocardiography to monitor the integrity and performance of the heart. It is the gold standard as it provides real-time imaging of the heart to enable early diagnosis and treatment.

Precordial doppler ultrasonography can also be used to detect into-operative air emboli. It is non-invasive and more practical, but is less sensitive.

A change in end-tidal CO2 could be indicative of and increase in physiological dead-space, but could also be indicative of any processes that reduces the excretion or increases the production of CO2, making it non-specific.

A transoesophageal stethoscope can be used to listen for the classic mill-wheel murmur produced by a large air embolus.

Key Point: While finding out confidence intervals, standard errors are used. Standard error and Standard deviation are two distinct entities and should not be confused.

For 99.7% confidence interval, you can find the range as follows:

Multiply the standard error by 3.

Subtract the answer from mean value to get the lower limit.

Add the answer obtained in step 1 from the mean value to get the upper limit.

The range turns out to be 1-13 mmol/L.

For a confidence interval of 68%, multiply the standard error with 1 and repeat the process. The range found for this interval is 3-11 mmol/L.

For a 95% confidence interval. Standard Error is multiplied by 1.96 which gives us the limit ranging from 3.08 to 10.92 mmol/L which could be approximated to 3-11 mmol/L.

Bilirubin is the tetrapyrrole and a catabolic product of heme. 70-90% of bilirubin is end product of haemoglobin degradation in the liver.

Bilirubin circulates in the blood in 2 forms; unconjugated and conjugated bilirubin.

Unconjugated bilirubin is insoluble in water. It travels through the bloodstream to the liver, where it changes from insoluble into a soluble form (i.e.; unconjugated into conjugated form).

This conjugated bilirubin travels from the liver into the small intestine and the gut bacteria convert bilirubin into urobilinogen and then into urobilin (not urobilin to urobilinogen). A very small amount passes into the kidneys and is excreted in urine.

Hawthorne effect explains the change in any behavioural aspect owing to the awareness that the person is being observed.
Simpson’s Paradox explains the association developed when the data from several groups is combined to form a single larger group.

The remaining terms are made up.

The cardiac action potential has several phases which have different mechanisms of action as seen below:
Phase 0: Rapid depolarisation – caused by a rapid sodium influx.
These channels automatically deactivate after a few ms

Phase 1: caused by early repolarisation and an efflux of potassium.

Phase 2: Plateau – caused by a slow influx of calcium.

Phase 3 – Final repolarisation – caused by an efflux of potassium.

Phase 4 – Restoration of ionic concentrations – The resting potential is restored by Na+/K+ATPase.
There is slow entry of Na+into the cell which decreases the potential difference until the threshold potential is reached. This then triggers a new action potential

Of note, cardiac muscle remains contracted 10-15 times longer than skeletal muscle.

Different sites have different conduction velocities:
1. Atrial conduction – Spreads along ordinary atrial myocardial fibres at 1 m/sec

2. AV node conduction – 0.05 m/sec

3. Ventricular conduction – Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles

The middle cerebral artery is a part of the circle of Willis system of anastomosis within the brain, and the most often affected by brain pathology.

The primary function of the middle cerebral artery is providing oxygenated blood to related regions of the brain. It achieves this by giving off different branches to supply different brain regions, namely:

The cortical branches: which supplies the primary motor and somatosensory cortical areas of some parts of the face, trunk and upper limbs.

The small central branches: which supply the basal ganglia and internal capsule via the lenticulostriate vessels.

The superior division: which supplies the lateral inferior frontal lobe, including the Broca area which is responsible for production of speech, language comprehension, and writing.

The inferior division: which supplies the superior temporal gyrus, including Wernicke’s area which controls speech comprehension and language development.

Taste sensation from the anterior two-thirds of the tongue is carried by chorda tympani, a branch of the facial nerve.

The general somatic sensation of the anterior two-third of the tongue is supplied by the lingual nerve, a branch of the mandibular nerve.

Both general somatic sensation and taste from the posterior third of the tongue are carried by the glossopharyngeal nerve.

All the muscles of the tongue except palatoglossus are supplied by the hypoglossal nerve whereas palatoglossus is supplied by the vagus nerve. (This is because palatoglossus is the only tongue muscle derived from the fourth branchial arch)

The patient likely suffers from pulmonary embolism due to her history of frequent international travels. A filter is placed in the inferior vena cava to decrease the risk of future episodes of pulmonary embolism. The IVC filter is a small, wiry device that can catch blood clots and stop them from going into the heart and lungs. Your IVC is a major vessel that brings deoxygenated blood from the lower body to the heart, from where it is pumped into the lungs.

The filter is placed via a thin catheter inserted into the femoral vein in the groin. The catheter is gently moved up into your IVC, and a filter is introduced.

The IVC is a retroperitoneal organ.

Endothelin-1 is considered as a powerful coronary vasoconstrictor, produced by the endothelium. It acts to counter the effects of Nitric oxide (NO).
Neuropeptide-Y, angiotensin1, cocaine, vasopressin, and nicotine are some other coronary vasoconstrictors.

Chronotrophy and inotrophy occur after the activation of sympathetic nerve fibres, which in turn results in increasing the myocardial oxygen consumption, leading to increased coronary blood flow via local metabolic processes.

An alpha-receptor mediated coronary vasoconstrictor effect is also initiated that usually competes with vasodilation, resulting in decreased coronary vascular resistance. Some of the other dilators include hydrogen ions, CO2, potassium, and lactic acid. The action of endothelial NO synthase (eNOS) on L-arginine results in the formation of NO. This messenger also plays a vital role in the regulation of coronary blood flow via vasodilation, inhibition of platelet aggression, and decreasing vascular resistance.
Adenosine is considered as purine nucleoside that forms after the breakdown of adenosine triphosphate (ATP). Adenosine binds to adenosine type 2A (A2A) receptors in coronary vascular smooth muscles. These are coupled to the Gs protein. This mechanism leads to hyperpolarisation of muscle cells, resulting in relaxation and increased coronary blood flow.

GTN is an veno and arteriolar dilator, which behaves as pro-drug with NO.

An agonist is a molecule with intrinsic efficacy and affinity for a receptor. The ability of a drug-receptor interaction to produce a maximal response is referred to as intrinsic efficacy or activity. Efficacy also refers to a drug’s ability to have a therapeutic or beneficial effect. Although the potencies of morphine and fentanyl differ, they both have the same intrinsic efficacy.

The amount of drug required to produce a given effect is referred to as potency. If drug X is effective in a dose of 100 mcg, its potency is greater than if drug Y is effective in a dose of 10 mg.

The therapeutic index, also known as the margin of safety, is a ratio of the lethal or serious side effect dose of a drug divided by the therapeutic dose of the same drug.

The term bioavailability refers to the ability of a substance to be absorbed. The area under a curve (AUC) of a graphic plot of plasma concentration and time is used to calculate oral bioavailability. It’s used to figure out how much of a drug to take and when to take it.

The pituitary gland plays a crucial role in the neuro-endocrine axis. It is located at the base of the skull in the sella turcica of the sphenoid bone. It is connected superiorly to the hypothalamus, third ventricle, and visual pathways, and laterally to the cavernous sinuses, internal carotid arteries, and cranial nerves III, IV, V, and VI.

Pituitary tumours make up about 10-15% of all intracranial tumours. The majority of adenomas are benign. Over-secretion of pituitary hormones (most commonly prolactin, growth hormone, or ACTH), under-secretion of hormones, or localised or generalised pressure effects can all cause symptoms.

Compression of the optic chiasm can result in visual field defects, the most common of which is bitemporal hemianopia. This is caused by compression of the nasal retinal fibres, which carry visual impulses from temporal vision across the optic chiasm to the contralateral sides before continuing to the optic tracts.

The interruption of the visual pathways distal to the optic chiasm causes a homonymous visual field defect. The loss of the right or left halves of each eye’s visual field is referred to as homonymous hemianopia. It’s usually caused by a middle or posterior cerebral artery territory stroke that affects the occipital lobe’s optic radiation or visual cortex.

Binasal hemianopia is a condition in which vision is lost in the inner half of both eyes (nasal or medial). It’s caused by compression of the temporal visual pathways, which don’t cross at the optic chiasm and instead continue to the ipsilateral optic tracts. Binasal hemianopia is a rare complication caused by the internal carotid artery impinging on the temporal (lateral) visual fibres.

A monocular visual loss (that is, loss of vision in only one eye) can be caused by a variety of factors, but if caused by nerve damage, the damage would be proximal to the optic chiasm on the ipsilateral side.

A central scotoma is another name for central visual field loss. Every normal mammalian eye has a scotoma, also known as a blind spot, in its field of vision. The optic disc is a region of the retina that lacks photoreceptor cells and is where the retinal ganglion cell axons that make up the optic nerve exit the retina. When both eyes are open, visual signals that are absent in one eye’s blind spot are provided for the other eye by the opposite visual cortex, even if the other eye is closed.

Scotomata can be caused by a variety of factors, including demyelinating disease such as multiple sclerosis, damage to nerve fibre layer in the retina, methyl alcohol, ethambutol, quinine, nutritional deficiencies, and vascular blockages either in the retina or in the optic nerve.

Bilateral scotoma can occur when a pituitary tumour compresses the optic chiasm, causing a bitemporal paracentral scotoma, which then spreads out to the periphery, causing bitemporal hemianopsia. A central scotoma in a pregnant woman could be a sign of severe pre-eclampsia.

The ventilation/perfusion ratio varies in different areas of the lung. In an upright individual, although both ventilation and perfusion increase from the apex to the base of the lung, the increase in ventilation is less than the increase in blood flow. As a result, the normal V̇ /Q̇ ratio at the apex of the lung is much greater than 1 (ventilation exceeds perfusion), whereas the V̇ /Q̇ ratio at the base of the lung is much less than 1 (perfusion exceeds ventilation).

There is more volume in the alveoli found in the apices than in the bases of the lungs. This is due to the weight of the lung stretching the apical alveoli to the maximum size. Also, the weight of the lungs pull themselves away from the chest wall, creating a negative intrapleural pressure. These factors, however, do not directly affect the PAO2.

A person remaining at high altitudes for days, weeks, or years becomes more and more acclimatized to the low PO2, so it causes fewer deleterious effects on the body.

After acclimatization, it becomes possible for the person to work harder without hypoxic effects or to ascend to still higher altitudes. The principal means by which acclimatization comes about are (1) a great increase in pulmonary ventilation, (2) increased numbers of red blood cells, (3) diffusing capacity of the lungs, (4) increased vascularity of the peripheral tissues, and (5) increased ability of the tissue cells to use oxygen despite low PO2.

The cardiac output often increases as much as 30% immediately after a person ascends to high altitude but then decreases back toward normal over a period of weeks as the blood haematocrit increases, so the amount of oxygen transported to the peripheral body tissues remains about normal.

The AAGBI and the British Hypertension Society has published guidelines for the measurement of adult blood pressure and management of hypertension before elective surgery.

The objective is to ensure that patients admitted for elective surgery have a known systolic blood pressure below 160 mmHg and diastolic blood pressures below 100 mmHg. The primary health care teams, if possible, should ensure that this is the case and provide evidence to the pre-assessment clinic staff or on admission.

Avoiding cancellation on the day of surgery because of white coat hypertension is a secondary objective.

Patients with blood pressures below 180 mmHg systolic and 110 mmHg diastolic (measured in the preop assessment clinic), who present to pre-operative assessment clinics without documented evidence of primary care blood pressures should proceed to elective surgery.

In this question, the history/assessment does not appear to point to obvious end-organ damage so there is no indication for further investigation for secondary causes of hypertension or an echocardiogram at this point. Further review and treatment at this point is not required.

However, you should write to the patient’s GP and encourage serial blood pressure measurements in the primary health care setting.

Arrhythmias and/or hypotension are the most common causes of death from tricyclic antidepressant (TCA) overdose.

The quinidine-like actions of tricyclic antidepressants on cardiac tissues are primarily responsible for their toxicity. Conduction through the His-Purkinje system and the myocardium slows as phase 0 depolarisation of the action potential slows. QRS prolongation and atrioventricular block are caused by slowed impulse conduction, which also contributes to ventricular arrhythmias and hypotension.

Arrhythmias can also be caused by abnormal repolarization, impaired automaticity, cholinergic blockade, and inhibition of neuronal catecholamine uptake, among other things.

Acidaemia, hypotension, and hyperthermia can all exacerbate toxicity.

The anticholinergic effects of tricyclic antidepressants, as well as the blockade of neuronal catecholamine reuptake, cause sinus tachycardia. Sinus tachycardia is usually well tolerated and does not require treatment. It can be difficult to tell the difference between sinus tachycardia and ventricular tachycardia with QRS prolongation.

A QRS duration of more than 100 milliseconds indicates a higher risk of arrhythmia and should be treated with systemic sodium bicarbonate.

The tricyclic is dissociated from myocardial sodium channels by serum alkalinization, and the extracellular sodium load improves sodium channel function.

Pituitary macroadenoma is a benign tumour with growth larger than 10mm (those under 10mm are called microadenoma)

Compression of optic chiasm by pituitary adenoma is responsible for causing visual field defects like bitemporal hemianopia, optic neuropathy.

The ASA physical status classification system is a system for assessing the fitness of patients before surgery. It was last updated in October 2014.

ASA I A normal healthy patient
ASA II A patient with mild systemic disease
ASA III A patient with severe systemic disease
ASA IV A patient with severe systemic disease that is a constant threat to life
ASA V A moribund patient who is not expected to survive without the operation
ASA VI A declared brain-dead patient whose organs are being removed for donor purposes

A 20-year old woman who is 39-weeks pregnant with no other medical conditions – ASA II

A 35-year-old man with a BMI of 29 with a good exercise tolerance who smokes-ASA II

A 50-year old man with a BMI of 41 with a reduced exercise tolerance -ASA III

A 65-year old woman with a BMI of 34 with treated hypertension with no functional limitations-ASA II

A 73-year old man who has had a TIA ten-weeks ago but has a good exercise tolerance and is a non-smoker-ASA IV

The central venous pressure (CVP) waveform depicts changes of pressure within the right atrium. Different parts of the waveform are:

A wave: which represents atrial contraction. It is synonymous with the P wave seen during an ECG. It is often eliminated in the presence of atrial fibrillation, and increased tricuspid stenosis, pulmonary stenosis and pulmonary hypertension.

C wave: which represents right ventricle contraction at the point where the tricuspid valve bulges into the right atrium. It is synonymous with the QRS complex seen on ECG.

X descent: which represents relaxation of the atrial diastole and a decrease in atrial pressure, due to the downward movement of the right ventricle as it contracts. It is synonymous with the point before the T wave on ECG.

V wave: which represents an increase in atrial pressure just before the opening of the tricuspid valve. It is synonymous with the point after the T wave on ECG. It is increased in the background of a tricuspid regurgitation.

Y descent: which represents the emptying of the atrium as the tricuspid valve opens to allow for blood flow into the ventricle in early diastole.

Canon waves: which refer to large waves present on the trace that do not correspond to the A, V or C waves. They usually occur in a background of complete heart blocks or junctional arrythmias.

The correlation coefficient gives us the idea about relation between two parameters. i.e. to what extent change in parameter A could prompt a change in parameter B. The numerical value of correlation coefficient could not be greater than 1.

The internal carotid artery passes through the carotid canal in the petrous part of the temporal bone into the cranial cavity. It does NOT groove the sphenoid bone.

The internal carotid artery gives off no branches in the neck and is a terminal branch of the common carotid artery.

These structures pass between the external and internal carotid arteries: the styloglossus and stylopharyngeus muscles, the glossopharyngeal nerve (CN IX), and the pharyngeal branch of the vagus.

Accompanied by its sympathetic plexus, the internal carotid artery, passes through the cavernous sinus and is crossed by the abducent nerve.

The cardiac action potential has several phases which have different mechanisms of action as seen below:
Phase 0: Rapid depolarisation – caused by a rapid sodium influx.
These channels automatically deactivate after a few ms

Phase 1: caused by early repolarisation and an efflux of potassium.

Phase 2: Plateau – caused by a slow influx of calcium.

Phase 3 – Final repolarisation – caused by an efflux of potassium.

Phase 4 – Restoration of ionic concentrations – The resting potential is restored by Na+/K+ATPase.
There is slow entry of Na+into the cell which decreases the potential difference until the threshold potential is reached. This then triggers a new action potential

Of note, cardiac muscle remains contracted 10-15 times longer than skeletal muscle.

Different sites have different conduction velocities:
1. Atrial conduction – Spreads along ordinary atrial myocardial fibres at 1 m/sec

2. AV node conduction – 0.05 m/sec

3. Ventricular conduction – Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles

The ?-2 adrenoceptor has three subtypes (2a, 2b and 2c). The receptors are generally presynaptic, meaning they prevent noradrenaline from being released at nerve endings. Both the central and peripheral nerve systems are affected by the ?-2 agonists. ?-2 agonists cause drowsiness, analgesia, and euphoria centrally in the locus coeruleus (in the brainstem), lower the MAC of volatile anaesthetic drugs, and are used to treat acute withdrawal symptoms in chronic opioid addicts.

The most common impact of ?-2 agonists on heart rate is bradycardia. The adrenoreceptors ?-1 and ?-2 are blocked by phenoxybenzamine.

Clonidine is a selective agonist for the ? -2 receptor, having a 200:1 affinity ratio for the ?-2: ?-1 receptors, respectively.

Tizanidine is similar to clonidine but has a few key variances. It has the same sedative, anxiolytic, and analgesic characteristics as clonidine, although for a shorter period of time and with less effect on heart rate and blood pressure.

Dexmedetomidine, like clonidine, is a highly selective ?-2 adrenoreceptor agonist having a higher affinity for the ?-2 receptor. In the case of ?-2: ?-1 receptors, the affinity ratio is 1620:1. It has a biphasic blood pressure impact and induces a brief rise in blood pressure and reflex bradycardia (activation of ?-2b subtypes of receptors in vascular smooth muscles), followed by a reduction in sympathetic outflow from the brainstem and hypotension/bradycardia.

A prodrug is methyldopa. It blocks the enzyme dopa-decarboxylase, which converts L-dopa to dopamine (a precursor of noradrenaline and adrenaline). It is also converted to alpha-methyl noradrenaline, a centrally active agonist of the ?-2 adrenoreceptor. These two processes contribute to its blood pressure-lowering effect. Without a rise in heart rate, cardiac output is generally maintained. The heart rate of certain patients is slowed.

Phentolamine is a short-acting antagonist of peripheral ?-1 and ?-2 receptors that causes peripheral vascular resistance to reduce and vasodilation to increase. It’s used to treat hypertensive situations that aren’t life threatening (e.g. hypertension from phaeochromocytoma).

A baroreceptor reflex commonly causes reflex tachycardia when systemic vascular resistance drops.

The membranous urethra is the shortest part of the urethra and the least dilatable part of it.

This is as a result of it being surrounded by the external urethral sphincter which is made up of striated muscle and controls voluntary urine flow from the bladder to the urethra.

The positive predictive value is the ratio of patients truly diagnosed as positive to all those who had positive test results. In this case, this is 60/(60+20)=75%.

The negative predictive value is the ratio of patients truly diagnosed as negative to all those who had negative test results. In this case, this is 80/(80+40)=67%.

The sensitivity is the ratio of patients with the disease who test positive i.e. true positive patients to the total number of people with the disease. In this case, this is 60/(60+40)=60%.

The specificity is the ratio of people who don’t have the disease who test negative i.e. true negatives to the total number of people without the disease. In this case, this is 80/(20+80)=80%.

70% is not the result of any screening measurements

Control of Substances Hazardous to Health (COSHH) was established by government under the Health and Safety at Work act in 1989. Their employers work on identification and management of those substances that are dangerous to health. The implications for anaesthetists include gas scavenging, equipment contamination and environmental safety. Adequate ventilation is required in areas where anaesthetic gases are present. The minimum air supply that is legally required in each specific area is: Operating theatres: 0.65 m3/second. Anaesthetic rooms: 0.15 m3/s. Preparation rooms: 0.1 m3/s. Recovery rooms need 15 air changes per hour

Number needed to treat (NNT) is a time specific epidemiological measure that indicates how many patients would be require for an intervention to prevent one additional bad outcome. A perfect NNT would be 1, where everyone improves with treatment, thus the higher the NNT, the less effective the treatment.

Thus if you treat 1000 patients then you will expect to have 50 fewer strokes.

The following are the colour codes for medical gas cylinders:

Oxygen cylinder has a dark body with white shoulders.

Nitrous oxide is French blue. Air encompasses a grey body with dark and white quarters on the shoulders.

Entonox contains a French blue body with white and blue quarters on the shoulders.

Carbon dioxide barrels are grey in colour.