When responsiveness diminishes rapidly after administration of a drug, the response is said to be subject to tachyphylaxis. This may be due to frequent or continuous exposure to agonists, which often results in short-term diminution of the receptor response.

Many mechanisms may be responsible, such as blocking access of G protein to activated receptor, or receptor molecules internalized by endocytosis to prevent exposure to extracellular molecules.

Tolerance occurs when larger doses are required to produce the same effect. This may be due to changes in receptor number or function due to exposure to the drug.

Desensitization refers to the common situation where the biological response to a drug diminishes when it is given continuously or repeatedly. It is a chronic loss of response, occurring over a longer period than tachyphylaxis. It may be possible to restore the response by increasing the dose (or concentration) of the drug but, in some cases, the tissues may become completely refractory to its effect.

Drug dependence is defined as a psychic and physical state of the person characterized by behavioural and other responses resulting in compulsions to take a drug, on a continuous or periodic basis in order to experience its psychic effect and at times to avoid the discomfort of its absence.

The right atrium receives blood supply from the SVC, IVC, and coronary sinus. It forms the right border of the heart.

The interior of the right atrium has 5 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 – an anterior rough, 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

The trabeculae carneae are irregular muscular elevations that form the interior of the right ventricle.

The respiratory quotient (RQ) is the proportion of CO2 produced by the body to O2 consumed per unit of time.

CO2 produced / O2 consumed = RQ

CO2 is produced at a rate of 200 mL per minute, while O2 is consumed at a rate of 250 mL per minute. An RQ of around 0.8 is typical for a mixed diet.

The RQ will change depending on the energy substrates consumed in the diet.

Granulated sugar is a refined carbohydrate that contains 99.999 percent carbohydrate and no lipids, proteins, minerals, or vitamins.

Glucose and other hexose sugars – RQ = 1
Fats – RQ = 0.7
Proteins – RQ is 0.9
Ethyl alcohol – RQ = 0.67

The internal jugular vein is found on both sides of the neck and collects blood from the brain, superficial regions of the face, and neck. It drains into the right atrium.

It is a continuation of the sigmoid sinus and begins in the posterior cranial fossa and exits the skull via the jugular foramen.
It runs within the carotid sheath as it descends in the neck and is accompanied by the vagus nerve posteriorly and the common carotid anteromedially.

The hypoglossal nerve emerges from the hypoglossal canal medial to the internal carotid artery and the internal jugular vein and ninth, tenth, and eleventh cranial nerves.

The internal jugular vein crosses anterior to the thoracic duct on the left side.

Bell’s palsy is facial muscle weakness or paralysis that arises from idiopathic damage to the facial nerve. It can occur at any age but is commonly associated with some conditions:
1. pregnancy
2. diabetes
3. upper respiratory ailment
4. GBS
5. Toxins

The common symptoms of Bell’s palsy are:
1. Abnormal corneal reflex as the facial nerve controls the motor aspect of the corneal reflex.
2. The loss of control of facial muscles and eyelids leads to decreased tear production.
3. mild weakness to total paralysis on one side of the face, occurring within hours to days.
4. Bell’s palsy is a lower motor neuron lesion that usually spares the forehead while the upper motor near lesions, like stroke, involves the entire face.
5. The anterior two-thirds of the tongue is supplied by the chorda tympani branch of the facial nerve, thus resulting in loss of taste.
6. Ptosis can be a feature of Bell’s palsy but Bell’s palsy would typically show unilateral symptoms rather than bilateral.

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.

The subclavian artery lies behind and partly above the subclavian vein. 3-4% of the time, it can be inadvertently cannulated during cannulation of the subclavian vein

Because of its anatomical position, putting pressure on the subclavian artery is impossible so arresting bleeding with pressure when it is punctured is not viable.

One of the consequences of subclavian vein cannulation (1%) is pleural puncture leading to a pneumothorax. This is because the apical pleura is inferior and caudal to the subclavian vein.

Oxytocin is structurally similar to Antidiuretic Hormone (ADH) and thus oxytocin can cause water intoxication (due to an ADH like action)

Oxytocin is secreted by the posterior pituitary along with ADH. It increases uterine contractions – the contraction of the upper segment (fundus and body) of the uterus whereas the lower segment is relaxed facilitating the expulsion of the foetus

Antidiuretic hormone (ADH) also called vasopressin is released from the posterior pituitary in response to hypertonicity and increases fluid reabsorption from the kidney.

The cephalic vein is one of the primary superficial veins of the upper limb. It overlies most of the fascial planes as it is located in the superficial fascia along the anterolateral surface of the biceps.

It originates in the anatomical snuffbox from the radial side of the superficial venous network of the dorsum of the hand. It travels laterally up the arm to join the basilic vein via the median cubital vein at the elbow.

Near the shoulder, it passes between the deltoid and pectoralis major muscles. It pierces the coracoid membrane (continuation of the clavipectoral fascia) to terminate in the axillary vein’s first part.

The nerve stimulators deliver a stimulus lasting for 1-2 milliseconds (not second) to perform nerve blockage.

There are just 2 leads (not 3); one for the skin and other for the needle.

Prior to the administration of the local anaesthesia, a current of 0.25 – 0.5 mA (not 1-2mA) at the frequency of 1-2 Hz is preferred.

If the needle tip is close to the nerve, muscular contraction could be possible at the lowest possible current.

Insulated needles have improved the block success rate, as the current is only conducting through needle tip.

Stimulus to the femoral nerve which is placed in the mid lingual line causes withdrawer of the quadriceps and knee extension, that’s the dancing patella ( not plantar flexion).

Glucose transport is a highly regulated process accomplished mostly by facilitated diffusion using carrier proteins to cross cell membranes.

There are many transporters, but the most important are known as glucose transporters (GLUTs).

Stresses in various form of acute and chronic forms affect the activity of glucose transporters.
They are responsive to many types of metabolic stress, including hypoxia, injury, hypoglycaemia, numerous metabolic inhibitors, stress hormones, and other influences such as growth factors.

Numerous signalling pathways appear to be involved in transporter regulation.

New evidence suggests that stresses regulating GLUTs are not only acute biological stresses. In addition, chronic low-grade inflammation, and their associated chronic diseases also lead to altered glucose transport. These include obesity, type 2 diabetes, cardiovascular disease, and the growth and spread of many tumours that are affected by altered glucose transporters. Some of these glucose transport effects are compensatory, while others are pathogenic.

Ultimately, deliberate manipulation of GLUTs could be used as treatment for some of these chronic diseases.

For the local anaesthetic base to be stable in solution, it is formulated as a hydrochloride salt. As such, the molecules exist in a quaternary, water-soluble state at the time of injection. However, this form will not penetrate the neuron. The time for onset of local anaesthesia is therefore predicated on the proportion of molecules that convert to the tertiary, lipid-soluble structure when exposed to physiologic pH (7.4).

The ionization constant (pKa) for the anaesthetic predicts the proportion of molecules that exists in each of these states. By definition, the pKa of a molecule represents the pH at which 50% of the molecules exist in the lipid-soluble tertiary form and 50% in the quaternary, water-soluble form. The pKa of all local anaesthetics is >7.4 (physiologic pH), and therefore a greater proportion the molecules exists in the quaternary, water-soluble form when injected into tissue having normal pH of 7.4.

Furthermore, the acidic environment associated with inflamed tissues favours the quaternary, water-soluble configuration even further. Presumably, this accounts for difficulty when attempting to anesthetize inflamed or infected tissues; fewer molecules exist as tertiary lipid-soluble forms that can penetrate nerves.

Level 1 – High-quality randomised controlled trial with statistically significant difference or no statistically significant difference but narrow confidence intervals (prospective controlled)

Level 2 – Prospective comparative study (prospective uncontrolled)

Level 3 – Case-control study, retrospective comparative study (retrospective controlled)

Level 4 – Case series (retrospective uncontrolled)

Level 5 – Expert opinion.

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.

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.

The bifurcation of the abdominal aorta into common iliac arteries occurs at the level of L4. The bifurcation is a common site for atherosclerotic plaques as it is an area of high turbulence.

Leriche Syndrome is an aortoiliac occlusive disease and affects the distal abdominal aorta, iliac arteries, and femoropopliteal vessels. It has a triad of symptoms:
1. Claudication (cramping lower extremities pain that is reproducible by exercise)
2. Impotence (reduced penile arterial flow)
3. Absent/weak femoral pulses (hallmark)

T12 – aorta enters the diaphragm with the thoracic duct and azygous veins

L2 – testicular or ovarian arteries branch off the aorta

L3 – inferior mesenteric artery

A significant early feature of the metabolic response to trauma and surgery is hyperglycaemia. It is due to an increased glucose production and decreased glucose utilisation bought on by neuroendocrine stimulation. Catecholamines, Growth hormone, ACTH and cortisol, and Glucagon are all increased.

There is also a decreased insulin sensitivity peripherally and an inhibition of insulin production from the beta cells of the pancreas. These changes lead to hyperglycaemia.

The stress response to endoscopic surgery will only be prevented with use of high dose opioids or central neuraxial block at anaesthesia.
To reduce the risk of inducing hyperchloremic acidosis, Ringer’s lactate/acetate or Hartmann’s solution is preferred to 0.9% sodium chloride as routine maintenance fluids.

Though it has been suggested that administration of Hartmann’s solution to patients with type 2 diabetes leads to hyperglycaemia, one Litre of Hartmann’s solution would yield a maximum of 14.5 mmol of glucose. A rapid infusion of this volume would increase the plasma glucose by no more than 1 mmol/L..

Dexamethasone, a glucocorticoid, produces hyperglycaemia by stimulating gluconeogenesis . Glucocorticoids are agonists of intracellular glucocorticoid receptors. Their effects are mainly mediated via altered protein synthesis via gene transcription and so the onset of action is slow. The onset of action of dexamethasone is about one to four hours and therefore would NOT contribute to the hyperglycaemia in this patient in the time given.

0.9% Normal saline with or without adrenaline is the usual irrigation fluid. With this type of surgery, systemic absorption is unlikely to occur.

Fentanyl is not likely the primary cause of hyperglycaemia in this patient. In high doses (50 mcg/Kg) it has been shown to reduce the hyperglycaemic responses to surgery.

Mid-shaft fractures of the humerus usually occur after a direct blow to the upper arm, which can occur after a fall or RTAs.
The most important clinical significance of a mid-shaft humeral fracture is an injury to the radial nerve. The radial nerve originates from the brachial plexus and has roots of C5-T1. It crosses the spiral groove on the posterior side of the shaft of the humerus.
On examination, the patient may have a wrist drop, loss or weakness of finger extension, and decreased or absent sensation to the posterior forearm, digits 1 to 3, and the radial half of the fourth digit.

The humeral shaft has two compartments:
1. Anterior:
Brachial artery and vein
Biceps brachii, brachialis, coracobrachialis
Musculocutaneous, median, and ulnar nerves
2. Posterior:
Radial nerve
Triceps

Other significant nerve injuries are:
1. Axillary nerve – surgical neck fracture of the humerus
2. Brachial Artery – supracondylar fracture of the humerus
3. Axillary artery – surgical neck fracture of the humerus, but is relatively uncommon

Certain skeletal muscles are more resistant to the effects of neuromuscular blocking agents, both non-depolarizing and depolarizing. The diaphragm is the most resistant. The muscles of the larynx and the corrugator supercilii are less resistant. The abdominal, orbicularis oris, and limb peripheral muscles are the most sensitive muscles.

Twitch stimulation patterns:

Supramaximal single stimulus:

The frequency ranges from 1 Hz to 0.1 Hz (one every second to one every 10 seconds)
The response is proportional to the frequency of the event.
It has limited clinical utility because it only tells you whether or not a patient is paralysed (no information on degree of paralysis).

Over the course of 0.5 seconds (2 Hz), four supramaximal stimulate were applied:

It is possible to see ‘fade’ and use it as a basis for evaluation.
This stimulation pattern is used to determine the degree of blockade (1-2 twitches is appropriate for abdominal surgery)
If the train of four (TOF) count is 1-2, reversal agents can be used in conjunction with medium-acting neuromuscular blocking agents.

Ratio of TOF:

This is the ratio of the 4th twitch amplitude to the 1st twitch amplitude.
The ratio decreases with non-depolarising block and is inversely proportional to the degree of block, allowing objective measurement of residual neuromuscular blockade.
To achieve adequate reversal, the ratio (as measured by accelerography) must be between 0.7 and 0.9.

Count of twitches after a tetanic experience(PTC):

50 Hz for 5 seconds, then a 3 second pause, followed by a single 1 Hz twitch stimulus.
When the TOF count is zero, this stimulation pattern is used to assess deep blockade (that is, in neurosurgery, microsurgery or ophthalmic surgery when even small movements of a patient will disturb the surgical field)
It gives an estimate of how long it will take for the response to return to single twitches, allowing assessment of blocks that are too deep for any other technique.
A palpable post-tetanic count (PTC) of 2 indicates no twitch response for about 20-30 minutes, and a PTC of 5 indicates no twitch response for about 10-15 minutes.

This is without a doubt the best way to keep track of paralysis in patients who need to avoid diaphragmatic movement. It’s best to use drug infusions and aim for a PTC of 2. After a tetanic stimulus, acetylcholine is mobilised, causing post-tetanic potentiation.

Stimulation in Two Bursts:

750 milliseconds between two short bursts of 50 Hz
This stimulation pattern is used to assess small amounts of residual blockade manually (tactile).

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.

The abdominal aorta begins at the level of the body of T12 near the midline, as a continuation of the thoracic aorta. It descends and bifurcates at the level of L4 into the common iliac arteries.

An abdominal aortic aneurysm is a swelling in the abdominal aorta. It most commonly occurs in men over 65 years old of age. Smoking, diabetes, hypertension, and hypercholesterolemia are other risk factors contributing to the disease.

The NHS screening program for abdominal aortic aneurysms involves an ultrasound test for men aged 65 or over if they have not undergone screening for a one-off screening test.

The oesophagus is a muscular tube that connects the pharynx to the stomach. It begins at the lower border of the cricoid cartilage and C6 vertebra. It ends at T11.

The oesophagus has physiological constrictions at the following levels:
1. Cervical constriction: Pharyngo-oesophageal junction (15 cm from the incisor teeth) produced by the cricopharyngeal part of the inferior pharyngeal constrictor muscle
2. Thoracic constrictions:
i. where the oesophagus is first crossed by the arch of the aorta (22.5 cm from the incisor teeth)
ii. where the oesophagus is crossed by the left main bronchus (27.5 cm from the incisor teeth)
3. Diaphragmatic constriction: where the oesophagus passes through the oesophageal hiatus of the diaphragm (40 cm from the incisor teeth)

Awareness of these constrictions is important for clinical purposes when it is required to pass instruments through the oesophagus into the stomach or when viewing radiographs of patients’ oesophagus.

The umbilical vein closes once the umbilical cord is clamped following birth. This causes a rise in systemic vascular resistance, closing the ductus venosus.

Upon birth, the pulmonary vascular resistance is decreased as the lungs are aerated.

At birth, there is a rise in oxygen tension which causes the corresponding constriction of the ductus arteriosus. This prevents a left to right shunt as it stops aortic blood and blood from the pulmonary artery from mixing. The ventricles do no have an opening connecting them.

The foramen ovale closes soon after birth. It is the septum opening between the left and right atrium.

An adult’s cardiac output is expected to be 5 L/min

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.

The statement Epinephrine is formulated as 1 in 1000 solution means 1 gm epinephrine is present in 1000 ml of solution.

The left marginal artery comes off the left circumflex artery, and runs alongside the heart.

The left circumflex artery is one of the bifurcations of the left coronary artery, and eventually forms the left marginal artery.

An occlusion in the left circumflex artery often results in a lateral MI.

The right marginal artery originates from the right coronary artery.

The left anterior descending artery (LAD) is another bifurcation of the left coronary artery. An occlusion in the LAD would often result in an anteroseptal MI as is diagnosed on ECG by noting changes in leads V1-V4.

The right coronary artery originates from the right aortic sinus of the ascending aorta, and bifurcates to give rise to many branches, including the sinoatrial artery which supplies the sinoatrial (SA) node in 50-70% of cases, the artery of the atrioventricular (AV) node in 50-60% of cases, the right acute marginal artery which supplies the right ventricle. It also supplies the right atrium, interatrial septum and the posterior inferior third of the interventricular septum.

Arrhythmias and inferior MI often occurs as a result of an occlusion in the right coronary artery, and can be diagnosed by ECG changes in leads II, III and aVF.

Metronidazole is a nitroimidazole antiprotozoal drug that is selectively absorbed by anaerobic bacteria and sensitive protozoa. Once taken up be anaerobes, it is nonenzymatically reduced by reacting with reduced ferredoxin. This reduction results in products that accumulate in and are toxic to anaerobic cells. The metabolites of metronidazole are taken up into bacterial DNA, forming unstable molecules. This action occurs only when metronidazole is partially reduced, and, because this reduction usually happens only in anaerobic cells, it has relatively little effect on human cells or aerobic bacteria.

Once the decision to deliver a baby by caesarean section has been made, it should be carried out with a level of urgency commensurate with the risk to the baby and the mother’s safety.

There are four types of caesarean section urgency:

Category 1 – Endangering the life of the mother or the foetus
Category 2 – Maternal or foetal compromise that is not immediately life threatening
Category 3 – Early delivery is required, but there is no risk to the mother or the foetus.
Category 4: Elective delivery at a time that is convenient for both the mother and the maternity staff.

Caesarean sections for categories 1 and 2 should be performed as soon as possible after the decision is made, especially for category 1. For category 1 caesarean sections, a decision to deliver time of 30 minutes is currently used.

In most cases, Category 2 caesarean sections should be performed within 75 minutes of making the decision.

The condition of the woman and the unborn baby should be considered when making a decision for a quick delivery, as it may be harmful in some cases.

There is no evidence of foetal compromise in the example above (early foetal pulse decelerations and a pH of less than 7.25). Early foetal pulse decelerations are most likely caused by the uterus compressing the foetal head. The foetus is not harmed by these. A spinal anaesthetic is preferred over a general anaesthetic whenever possible.

If the foetal scalp blood pH is greater than 7.25, it’s a good idea to repeat the test later and look for any changes. When a foetus decelerates, the mother should be given oxygen, kept in a left lateral position, and kept hydrated to avoid the need for a caesarean section.

A forest plot is a graphical representation that summarizes the findings of several research, such as a meta-analysis of a series of randomized controlled trials.

The Kaplan-Meier estimate shows survival over time, for example, plotting the number of patients still alive seven years after chemotherapy for lung cancer.

Fisher’s exact test similarly uses contingency tables to assess statistical significance, however, it is typically used when sample sizes are small.

Chi-square test assesses whether an association exists between two categorical variables using the observed and expected frequencies. For instance, is social class (I-V) related to body mass index (BMI) category? Using the observed and anticipated frequencies, the Chi-square test determines whether a connection exists between two categorical variables. For example, is socio-economic status related to BMI category?

Linear regression is a technique which attempts to model the relationship between two variables by fitting a linear equation to observed data. Linear regression uses correlation between two continuous variables. As correlation only indicates the strength of an association only, it cannot be used to forecast the change in one variable when a second variable is altered.

This equation takes the form y = mx + c, where ‘y’ is the dependent variable, ‘x’ is the independent variable, ‘m’ is the slope of the line and ‘c’ is the intercept. In this example, for a range of heights, it would be possible to map a line of best fit to a scatter plot and thus predict the forced expiratory volume (FEV1) for an individual.

The inguinal canal is the pathway leading from the wall of the abdomen to the external genitalia.

The borders of the inguinal canal are:

Anterior wall: formed by the aponeurosis of the external oblique, supported by the internal oblique muscle laterally.

Posterior wall: formed laterally by the transversalis fascia, and medially by the conjoint tendon

Roof: formed by the internal oblique and transversus abdominis muscles

Floor: formed by the inguinal ligament and supported medially by the lacunar ligament

Because of the low pH in the stomach, paracetamol absorption is minimal (pKa value is 9.5). Paracetamol is absorbed quickly and completely in the alkaline environment of the small intestine. Oral bioavailability is approaching 100%. As a result, measuring paracetamol levels in plasma after an oral paracetamol dose has been used as a surrogate marker of gastric emptying. This method has been used to investigate the effects of drugs on gastric emptying. At clinically used doses, paracetamol is ideal because it has very few side effects.

Scintigraphic imaging is the gold standard for determining gastric emptying.

Although aspirin (acetyl salicylic acid) is absorbed primarily in the small intestine, some may also be absorbed in the stomach. The oral bioavailability ranges from 70 to 100 percent, making it less reliable than paracetamol.

Propranolol is a lipophilic drug that is rapidly absorbed after administration. However, it is highly metabolised by the liver in the first pass, and only about 25% of propranolol reaches the systemic circulation. It’s not the best indicator of gastric emptying.

Oral bioavailability of gentamicin and vancomycin is low. Only antibiotic-induced pseudomembranous colitis is treated with oral vancomycin.

Erythromycin is a pro-kinetic agent that acts as a motilin receptor agonist.

The blood vessel well is divided into 3 parts, namely:

The tunica intima, which is the deepest layer. It contains endothelial cells separated by gap junctions

The tunica media, primarily consisting of the involuntary smooth muscle fibres, laid out in spiral layers with elastic fibres and connective tissue.

The tunica adventitia, which is the most superficial layer. It consists of the vasa vasorum, fibroblast and collagen.

The inferior mesenteric artery originates 3-4 cm above the bifurcation of the abdominal aorta. The left colic artery branches off the inferior mesenteric artery, arising close to its origin from the abdominal aorta. Other branches of IMA include the three sigmoid arteries that supply the sigmoid colon.

The left colic artery branches off from IMA to supply the distal 1/3 of the transverse colon and the descending colon. It moves upwards posterior to the left colic mesentery and then travels anteriorly to the psoas major muscle, left ureter, and left internal spermatic vessels, before dividing into ascending and descending branches.

Normally, at rest vagal influence is dominant producing the heart rate of 60-80 beats per minute even if the intrinsic automaticity of Sinoatrial Node is 100-110 beats per minute.

The transplanted heart has no autonomic nervous supply. So, it will respond to endogenous and exogenous catecholamine. This loss of parasympathetic innervation is responsible for the tachycardia in this patient.

Hypokalaemia can cause myocardial excitability and potential for ventricular ectopic and supraventricular arrhythmias. Hypothyroidism is also unlikely to cause tachycardia in this patient.

The most important determinant of preoxygenation adequacy is expired fraction of oxygen. Denitrogenating of the functional residual capacity is the purpose of preoxygenation. This is dependent on three vital factors: (1) respiratory rate; (2) inspired volume, and; (3) inspired oxygen concentration (FiO2).

Arterial oxygen saturation does not efficiently determine adequacy of preoxygenation because of its inability to measure tissue reserves. Arterial partial pressure of oxygen is also unsuitable for determining preoxygenation adequacy. Moreover, the absence of central cyanosis is a very crude sign of low tissue oxygenation.

Since the gas is less dense at higher altitudes, the density of a gas influences flows when passing through the orifice. Due to this reason, for a given flow rate, the bobbin will not be forced as far up the rotameter tube.

At higher altitudes, the volume of a fixed mass of gas increases, and therefore the molecules of gas are widely spaced resulting in a decrease in density with an increase in altitude.

Viscosity is simply termed as friction of gas. The viscosity of a gas is important only at low flow rates when the flow characteristic of the gas is laminar.

Charle’s law stated that the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature (T) provided the pressure remains constant.

Boyle’s law for a fixed amount of gas at constant temperature, the pressure (P) and volume (V) are inversely proportional.

Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions.

A compound that contains an asymmetric centre (chiral atom or chiral centre) and thus can occur in two non-superimposable mirror-image forms (enantiomers) are called chiral compounds.

Desflurane, Halothane, and isoflurane are chiral compounds but Sevoflurane is not a chiral compound.

Mesenteric ischemia is ischemia of the blood vessels of the intestines. It can be life-threatening, especially if the small intestine is involved.

The inferior mesenteric artery originates 3-4 cm above the bifurcation of the abdominal aorta.
The left colic artery branches off the inferior mesenteric artery to supply the following:
– distal 1/3 of the transverse colon
– descending colon

At approximately the left colic flexure (splenic flexure), a transition occurs in the blood supply of the GI tract. The SMA supplies the proximal part to the flexure, and the IMA supplies the part distal to the flexure. This is why the left colic flexure is a watershed area and is prone to ischemia exacerbated by atherosclerotic changes or hypotension. The dominant arterial supply of the splenic flexure is usually from the left colic artery, but it may also get collaterals from the left branch of the middle colic artery.

The AMA and PMA do not exist.
The splenic artery directly supplies the spleen and has branches that supply the stomach and the pancreas.
The proximal two-thirds of the transverse colon is supplied by the middle colic artery, a branch of the SMA.

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

Vancomycin binds to the acyl-D-ala-D-ala portion of the growing cell wall in a susceptible gram-positive bacterium. After binding, it prevents the cell wall from forming the cross-linking.

Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Tetrahydrofolic acid is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.

This question is asking which structure would lie posterior to the rectus abdominis muscle and not the prosthetic mesh, as only peritoneum lies posterior to mesh during a total extraperitoneal (TEP) hernia repair.

The region of the repair lies below the arcuate line, meaning that the transversalis fascia and peritoneum lie posterior to the rectus abdominis.

The bucks fascia lies within the penis.

Parotidectomy is basically an anatomical dissection. Identification of the facial nerve trunk is essential during parotid gland surgery because facial nerve injury is the most daunting potential complication of parotid gland surgery owing to the close relation between the gland and the extratemporal course of the facial nerve. After exiting the stylomastoid foramen, the facial nerve enters the substance of the parotid gland and then gives off five terminal branches:
From superior to inferior, these are the:
– Temporal branch supplying the extrinsic ear muscles, occipitofrontalis and orbicularis oculi
– Zygomatic branch supplying orbicularis oculi
– Buccal branch supplying buccinator and the lip muscles
– Mandibular branch supplying the muscles of the lower lip and chin
– Cervical branch supplying platysma.

There are two approaches to identify the facial nerve trunk during parotidectomy—conventional antegrade dissection of the facial nerve, and retrograde dissection. Numerous soft tissue and bony landmarks have been proposed to assist the surgeon in the early identification of this nerve. Most commonly used anatomical landmarks to identify facial nerve trunk are stylomastoid foramen, tympanomastoid suture (TMS), posterior belly of digastric (PBD), tragal pointer (TP), mastoid process and peripheral branches of the facial nerve.

An intercostal nerve block is used for therapeutic and diagnostic purposes. Intercostal nerve blocks manage acute and chronic pain in the chest area. Common indications are chest wall surgery and shingles or postherpetic neuralgia.

An intercostal nerve block is also an effective option for the management of pain associated with chest trauma and rib fractures. These blocks have been shown to improve oxygenation and respiratory mechanics, and offer pain relief that is comparable to that of epidural analgesia.

This technique, however, is limited by the relatively large doses of local anaesthetic required, and relatively high intravascular uptake from the intercostal space, increasing risk of local anaesthetic toxicity.

Mivacurium, when administered at doses greater than 0.2 mg/kg,increases the risk for hypotension, tachycardia, and erythema. This is due to the ability of mivacurium to release histamine with increasing dose. Contrary to this fact, anaphylaxis is rare for mivacurium because of the short duration of histamine release.

The effective dose 50 (ED50) of mivacurium is between 0.08-0.15 mg/kg. It is administered slowly to prevent and decrease the risk of developing adverse effects.

Mivacurium has a high potency thus a longer duration of action, however this is not the answer that we are looking for.

Although drug metabolism takes longer for mivacurium than succinylcholine, it has no effect on the dose required for intubation.

The potential difference (amplitude) and bandwidth frequencies of bioelectric signals are typical.

These are the following:

ECG: A bandwidth of 0.5-50 Hz is usually sufficient in monitoring mode, but a typical diagnostic bandwidth is 0.05-150 Hz (up to 200 Hz) with a typical voltage range of 0.1-4 millivolts (100-4000 microvolts).
EEG has a frequency range of 0.5-100 Hz and a voltage range of 0.5-100 microvolts.
EMG has a frequency range of 0.5 to 350 Hz and a voltage range of 0.5 to 30 millivolts.

Prior to display, these small signals will need to be amplified and processed further.

Prerenal failure has a serum urea: creatinine ratio of >100, while acute kidney injury has a ratio of 40.
In prerenal failure, ADH levels are typically high, resulting in water, urea, and sodium resorption. The fractional sodium excretion is less than 1%, but it is greater than 2% in acute tubular necrosis.
Prerenal azotaemia has higher serum urea nitrogen/serum creatinine ratios (>20), whereas acute tubular necrosis has lower ratios (10-15). The normal range is between 12 and 20.
Urinary sodium is less than 20 in prerenal failure and greater than 40 in acute tubular necrosis.
Prerenal failure has a urine osmolality of >500, while acute tubular necrosis has an osmolality of 350.
Prerenal failure has a urine/serum creatinine ratio of >40, while acute tubular necrosis has a urine/serum creatinine ratio of 20.

The concentrations of serum urea or creatinine change in inverse proportion to glomerular filtration. Changes in serum creatinine concentrations are more reliable than changes in serum urea concentrations in predicting GFR. Creatinine is produced at a constant rate from creatine, and blood concentrations are almost entirely determined by GFR.

A number of factors influence urea formation, including liver function, protein intake, and protein catabolism rate. Urea excretion is also influenced by hydration status, the amount of water reabsorption, and GFR.

A high serum creatinine level, as well as a urine output of less than 10 mL/hour and the production of concentrated looking urine, do not necessarily indicate a specific cause of oliguria.

The oxygen content of arterial blood can be calculated by the following equation:
(10 x haemoglobin x SaO2 x 1.34) + (PaO2 x 0.0225).
This is the sum of the oxygen bound to haemoglobin and the oxygen dissolved in the plasma.

Oxygen content x cardiac output = The amount of oxygen delivered to the tissues in unit time which is known as the oxygen flux.

Any factor that increases the metabolic demand will encourage oxygen offloading from the haemoglobin in the tissues and this causes the oxygen dissociation curve (ODC) to shift to the right. This subsequently reduced the oxygen content of arterial blood.

Conditions like fever, metabolic or respiratory acidosis lowers the oxygen content and shifts the ODC to the right.
A low level of 2,3 diphosphoglycerate (2,3-DPG) is usually related to an increased oxygen content as there is less offloading, and so the ODC is shifted to the left.

So for a given PaO2, a high blood oxygen content is related to any factors that can shift the ODC to the left and not to the right.

A low haematocrit usually means that there is a decreased haemoglobin concentration, and therefore is associated with decreased oxygen binding to haemoglobin.

The spinous process is the part of a vertebrae that is directed posteriorly.

Typical cervical vertebra have spinous processes that are small and bifid, except for C7, which has a long and prominent spinous process.

Multiple regression analysis revealed that velocity of lactate accumulation (VOBLA) accounted for 92 percent of the variation in marathon running velocity (VM), and VOBLA plus training volume prior to the marathon accounted for 96 percent of the variation. Percent ST muscle fibre distribution (r = 0.55-0.69) and capillary density (r = 052-0.63) were found to be positively correlated with all performance variables. As a result, marathon running performance was linked to VOBLA and the ability to run at a pace close to it during the race. The percent ST, capillary density, and training volume were all related to these properties.

Another metabolic adaptation compared to normal people is the early selection of fat for oxidation by muscle, especially when glucose availability is limited during high-intensity exercise. This helps to delay the onset of muscle fatigue, but it does not prevent VOBLA.

For a given level of exercise, training can also result in cardiovascular adaptation, such as increased heart size, increased contractility, and a slower heart rate. All of these factors contribute to an increase in maximal oxygen consumption (VO2 max), but genetic factors, despite intensive training, play a large role in an athlete’s performance.

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.

Prednisolone 5 mg is the same as 20 mg hydrocortisone.

Prednisolone 40 mg is the same as 8 x 20 mg or 160 mg of prednisolone.

Mineralocorticoid effects and variations in action duration are not taken into account in these comparisons.

5 mg of prednisolone is the same as Dexamethasone 750 mcg, Hydrocortisone 20 mg, Methylprednisolone 4 mg, and Cortisone acetate 25 mg.

A hernia is a protrusion of the abdominal viscera through a defect in the abdominal wall. Inguinal hernias are of two types; Indirect inguinal hernia and Direct inguinal hernia.
– Indirect inguinal hernia is common at young age commonly due to a patent processes vaginalis and bowel passes through the deep inguinal ring lateral to the inferior epigastric artery.
– Direct hernia forms as a result of the weakening of the posterior wall of the inguinal canal more specifically within a region called ‘Hasselbach triangle. It is defined medially by the rectus abdominis muscle, laterally by the epigastric vessels, and inferiorly by the inguinal ligament.

Direct and indirect hernias can be differentiated based on their relation to the inferior epigastric artery. Direct inguinal hernia lies medial to it while indirect inguinal hernia lies lateral to the inferior epigastric artery.

The femoral ring is the site of the femoral hernia.

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 starling forces operate to maintain a homeostatic flow across the pulmonary capillary bed.

The outward driving force comprises of the capillary hydrostatic pressure (13 mmHg), negative interstitial fluid pressure (zero to slightly negative), and interstitial colloid osmotic pressure (17 mmHg). The inward driving force is controlled by the plasma colloid osmotic pressure (25 mmHg).

Calcium channel blocker (CCB) blocks L-type of voltage-gated calcium channels present in blood vessels and the heart. By inhibiting the calcium channels, these agents decrease the frequency of opening of calcium channels activity of the heart, decrease heart rate, AV conduction, and contractility.

Three groups of CCBs include
1) Phenylalkylamines: Verapamil, Norverapamil
2) Benzothiazepines : Diltiazem
3) Dihydropyridine : Nifedipine, Nicardipine, Nimodipine, Nislodipine, Nitrendipine, Isradipine, Lacidipine, Felodipine and Amlodipine.

Even though verapamil as good absorption from GIT, its oral bioavailability is low due to high first-pass metabolism.

Nimodipine is a Cerebro-selective CCB, used to reverse the compensatory vasoconstriction after sub-arachnoid haemorrhage and is more lipid soluble analogue of nifedipine

Calcium channel antagonist can potentiate the effect of non-depolarising muscle relaxants.

The patellar (knee jerk) reflex is a monosynaptic stretch reflex arising from L2-L4 nerve roots. It occurs after a tap on the patellar tendon which causes the spindles of the quadriceps muscles to stretch.

The afferent nerve pathway occurred through A gamma fibres.

Wesphal’s sign refers to a reduction, or absence of the patellar reflex. It is often indicated of a neurological disease affecting the PNS.

A transection of the spinal cord results in a degree of shock which causes all reflexes to be reduced or completely absent, and required a period of approximately 6 weeks to recover.

The adrenal medulla comprises chromaffin cells (pheochromocytes), which are functionally equivalent to postganglionic sympathetic neurons. They synthesize, store and release the catecholamines noradrenaline (norepinephrine) and adrenaline (epinephrine) into the venous sinusoids.
The majority of the chromaffin cells synthesize adrenaline.

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

Amyl nitrate is part of the treatment of cyanide poisoning. The short acting nitrate causes oxidation of Fe2+ in haemoglobin to Fe3+ in methaemoglobin. Methaemoglobin combines with cyanide (cyanmethemoglobin), which reacts with sodium thiosulfate to convert nontoxic thiocyanate and methaemoglobin.

Methaemoglobin is formed when the iron in haemoglobin is converted from the reduced state (Fe2+) to the oxidized state (Fe3+). The oxidized form of haemoglobin (Fe3+) does not bind oxygen as readily as Fe2+, but has high affinity for cyanide. It also results to high affinity of bound oxygen to haemoglobin, thus leading to tissue hypoxia. Arterial oxygen tension is normal despite observations of cyanosis and dyspnoea. Methemoglobinemia can be treated with methylene blue and vitamin C.

Carboxyhaemoglobin can be due to carbon monoxide poisoning. In such cases, patients experience headache and dizziness, but do not develop cyanosis.

2,3-diphosphoglycerate causes a shift in the oxygen dissociation curve to the right, decreasing haemoglobin’s affinity to oxygen to facilitate unloading of oxygen to the tissues.

The following is the alveolar gas equation:

PAO2 = PiO2 − PaCO2/R

Where:

PAO2 is the partial pressure of oxygen in the alveoli.
PiO2 is the partial pressure of oxygen inhaled.
PaCO2 stands for partial pressure of carbon dioxide in the arteries.
The amount of carbon dioxide produced (200 mL/minute) divided by the amount of oxygen consumed (250 mL/minute) equals R = respiratory quotient. With a normal diet, the value is 0.8.

By subtracting the partial pressure exerted by water vapour at body temperature, the PiO2 can be calculated:

PiO2 = 0.21 × (100 kPa − 6.3 kPa)
PiO2 = 19.8

Substituting:
PAO2 = 19.8 − 10/0.8
PAO2 = 19.8 − 12.5
PAO2 = 7.3k Pa

The renal arteries branch from the abdominal aorta just below the origin of the superior mesenteric artery. The right renal artery is higher and longer than the left renal artery. The left renal artery passes behind the left renal vein, the body of the pancreas, and the splenic vein.

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

T10 – oesophageal opening in the diaphragm

T12 – Coeliac trunk, aortic hiatus in the diaphragm

L1 – Left renal artery

L2 – Testicular or ovarian arteries

L3 – Inferior mesenteric artery

L4 – Bifurcation of the abdominal aorta

The ideal agent for this case should have low blood: gas coefficient, pleasant smell, and high oil: gas coefficient (potent with a low Minimum alveolar coefficient (MAC)). Among the given options, Sevoflurane is perfect with 0.692 blood: gas partition coefficient and is low pungency, and is sweet.

Other drugs with their blood: gas partition coefficient and their smell are given as:
Blood/gas partition coefficient MAC Smell
Enflurane 1.8 1.68 Pungent, ethereal
Desflurane 0.42 7 Pungent, ethereal
Halothane 2.54 0.71 Sweet
Isoflurane 1.4 1.15 Pungent, ethereal

The pH of CSF is 7.31 which is lower than plasma.

Compared to plasma, it has a lower concentration of potassium, calcium, and protein and a higher concentration of sodium, chloride, bicarbonate and magnesium.

CSF usually has no cells present but if white cells are present, there should be no more than 4/ml.

The pressure of CSF should be less than 20 cm of water.

The concentration of glucose is approximately two-thirds of that of plasma, and it has a concentration of approximately 3.3-4 mmol/L.

Detsky’s Modified cardiac risk classification system in patients undergoing non-cardiac surgery:

Age more than 70: 05 points

History of myocardial infarction:

Less than 6 months: 10 points
More than 6 months: 5 points

Angina Pectoris:

Angina with minimal exertion: 10 points

Angina at any level of exertion: 20 points

Pulmonary Oedema:

Within 7 days: 10 points
At any time: 5 points

Suspected aortic valve stenosis with valve area <0.6cm2: 20 points Arrhythmia: Any rhythm other than sinus or sinus with premature atrial complexes (PACs): 5 points More than 5 premature ventricular contractions: 5 points
Emergency Surgery: 10 points
Deficient general medical condition: 5 points

Risk classification:

Grade I: 0-15 points = low risk
Grade II: 15-30 points = moderate risk
Grade III: >30 points = high risk

A patient presenting with symptomatic asthma should be assessed for severity to determine appropriate management options. Indications of acute severe asthma are:

Peak expiratory flow rate (PEFR): 33-50% best/predicted
Respiratory rate: ≥25/min
Heart rate: ≥110/min
Inability to finish a complete sentence in a single breath.

Oxygen saturation should be measured. Any measurement of an oxygen saturation of 92% or less, either on air or on oxygen, indicates severe, life threatening asthma, and requires an arterial blood gas (ABG) to detect normo- or hypercarbia.

A chest x-ray would not be routine as it will not provide any relevant information. It is only required in specific cases, including:
Diagnosis of a subcutaneous emphysema
Indications of a unilateral pneumothorax
Indications of a lobar collapse of consolidation
Treatment-resistance life-threatening asthma
If mechanical ventilation is indicated

A peak expiratory flow rate (PEFR) can provide relevant information to help distinguish between acute, moderate, severe and life threatening asthma. However, it is not necessary as other parameters exist that can also help make the same distinction.

An ECG is indicated in this case as the patient has tachycardia and tachypnoea which are indicative of acute severe asthma. The ECG would indicate if arrhythmia is also present which would suggest life-threatening asthma.

The study is being conducted on a smaller level with only 200 participants and is determining the effectiveness of the drug in comparison to a placebo. These characteristics are in accordance with the second phase of trial.

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.

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.

Ferromagnetism is the property of a substance that is magnetically attracted and can be magnetised indefinitely. A material is said to be paramagnetic if it is attracted to a magnetic field. A substance is said to be diamagnetic if it is repelled by a magnetic field.

Cobalt, iron, gadolinium, neodymium, and nickel are ferromagnetic.

Gadolinium is a ferromagnetic rare earth metal that is ferromagnetic below 20 degrees Celsius (its Curie temperature). MRI scans are enhanced with gadolinium-based contrast media.

When ferromagnetic materials are exposed to a magnetic field, they can cause a variety of issues like magnetic field interactions, heating, and image artefacts.

Titanium, lead, chromium, copper, aluminium, silver, gold, and tin are non ferromagnetic.

The tricuspid valve allows the tip of a pulmonary artery catheter to pass through the right atrium and into the right ventricle.

The balloon will be inflated before crossing the pulmonary valve and entering the pulmonary artery, where it will eventually wedge or occlude the artery, providing an indirect measure of left atrial pressure.

0-12 mmHg in the right atrium
2-25 mmHg in the right ventricle
12-25 mmHg in the pulmonary artery
8-12 mmHg is the occlusion pressure

There are different effects of electrocution and these can be shown in the table below.

Current Effect
1 mA Tingling
5 mA Pain
15 mA Tonic muscle contraction
50 mA Respiratory arrest
100 mA Ventricular fibrillation and cardiac arrest

The portal vein arises from the splenic and mesenteric veins, and is the biggest vessel in the portal venous system, accounting for about 75% of the hepatic blood flow.

It is responsible for draining blood from parts of the gastrointestinal system, the spleen, the pancreas and the gallbladder into the liver.

A ‘double blind crossover study’ happens when every patient receive both treatments.

It is incorrect to say that only half of the patients do not know which treatment they receive because in a double blind placebo control clinical trial ALL of the patients are blind to their treatment choice .

If some of the patients are not treated, they would be aware that they were not being treated and it could not be considered a blind trial.

In a double blind placebo control clinical trial both the clinician and the patient are blind to the treatment choice. The clinician assessing the effects of the treatment, therefore, does not know which treatment the patient has been given.

Since an arterial pressure transducer, and every other measuring apparatus, is prone to errors due to offset and gradient drifts, regular calibration is required to maintain accuracy of the instrument. The two-point calibration pressure values of 0 mmHg and 200 mmHg are within the physiologic range and can best compensate for the gradient drift.

During normal tissue metabolism, there is production of CO2 (acid) which is then expired by the lungs. If metabolism switches from aerobic to anaerobic due to a lack of oxygen, the tissues are unable to completely oxidise sugars to CO2. As a consequence, the sugars can only be partially oxidised to lactic acid. Since lactic acid cannot be expired by the lungs, it remains in the circulation leading to metabolic acidosis.

Also, normal tissue metabolism leads to the production of some amount of acid from the breakdown of proteins. These acids are excreted from the body by kidney filtration. Renal failure will therefore results in acidosis after several days.

An increased acidosis stimulates the brain’s respiratory centres to increase the respiratory rate. This lowers the CO2 in the blood, leading to a decrease in its acidity. Renal excretion removes the excess acid, resulting in a normal pH, and a reduced PaCO2 and HCO3.

pH PaCO2 (kPa) HCO3
Compensated respiratory acidosis 7.34 7.2 29
Acute respiratory acidosis 7.25 7.3 22
Compensated metabolic acidosis 7.34 3.6 14
Metabolic acidosis 7.21 5.3 15
Metabolic alkalosis 7.51 5.1 30

The abdominal aorta begins at the level of the body of T12 near the midline, as a continuation of the thoracic aorta. It descends and bifurcates at the level of L4 into the common iliac arteries.

The branches of the abdominal aorta (with their vertebra level) are:
1. Inferior phrenic arteries: T12 (upper border)
2. Coeliac artery: T12
3. Superior mesenteric artery: L1
4. Middle suprarenal arteries: L1
5. Renal arteries: Between L1 and L2
6. Gonadal arteries: L2 (in males, it is the testicular artery, and in females, the ovarian artery)
7. Inferior mesenteric artery: L3
8. Median sacral artery: L4
9. Lumbar arteries: Between L1 and L4

The superior phrenic artery branches from the thoracic aorta.

Chi-square test is used to determine the statistically significant different between categorical variables. It also determines the difference between expected frequencies and the observed frequencies.

Mann Whitney U test is used to determine the statistically significant different between two independent groups.

Wilcoxon’s test is the test of dependency. it determines the statistically significant difference between two dependent groups.

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.

ANOVA (analysis of variance) is similar to student’s t-test.

ANOVA is a statistical method used to determines the statistically significant difference between the mean of more than two group. In this experiment as we are dealing with three different group, ANOVA is most suitable test to determine the difference between each groups.

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).

Whatever the age, the dead space ratio is 0.3. It’s the dead space (Vd) to tidal volume ratio (Vt).

The glottis is the narrowest point of the upper airway in an adult, while the cricoid ring is the narrowest point in a child.

A child’s airway resistance is much higher than an adult’s. The resistance to airflow increases as the diameter of a paediatric airway shrinks. The radius (r) to the power of 4 is inversely proportional to airway resistance (r4). As a result, paediatric patients are more susceptible to changes in airflow caused by a small reduction in airway diameter, such as caused by oedema.

The compliance of a newborn’s lungs is very low (5 mL/cmH2O), but it gradually improves as lung size and elasticity grow. Lung compliance in an adult is 200 mL/cmH2O.

In children, minute ventilation (mL/kg/minute) is much higher.

Changes in the osmolality of body fluids (changes as minor as 1% are sufficient) play the most important role in regulating AVP secretion. The receptors that monitor changes in osmolality of body fluids (termed osmoreceptors) are distinct from the cells that synthesize and secrete AVP, and are located in the organum vasculosum of the lamina terminalis (OVLT) of the hypothalamus. The osmoreceptors sense changes in body osmolality by either shrinking or swelling. When the effective osmolality of the plasma increases, the osmoreceptors send signals to the AVP synthesizing/secreting cells located in the supraoptic and paraventricular nuclei of the hypothalamus, and AVP synthesis and secretion are stimulated. Conversely, when the effective osmolality of the plasma is reduced, secretion is inhibited. Because AVP is rapidly degraded in the plasma, circulating levels can be reduced to zero within minutes after secretion is inhibited.

In this scenario, the osmolality of the plasma will decrease to an estimate of 2.5%, hence inhibition of AVP.

Stimulation of atrial stretch receptors is incorrect because the increase in plasma volume is still below the threshold for its activation.

Osmotic diuresis is incorrect because 5% dextrose is isotonic, hence osmotic diuresis is not probable.

Renin is inhibited when an excess of NaCl in the tubular fluid is sensed by the macula densa.

The correct answer is the mean, median and mode of normally distributed data are the same value. This is as a result of the bell shaped curve which is equal on both sides.

The bell-shape indicates that values around the mean are more frequent in occurrence than the values farther away.

In a normal distribution:
1) +/- one standard deviation of the mean accounts for 68% of the data.
2) +/- two standard deviations of the mean accounts for 95% of the data.
3) +/- three standard deviations of the mean accounts for 99.7% of the data.

A stock dose of Intravenous paracetamol available in the market is 10mg/ml. There is a recommended dose of IV paracetamol according to the profile of the patient (age, co-morbidities, weight).

Weight Recommended Dose Maximum per day
≤10 kg 7.5 mg/kg 30 mg/kg
>10 kg to ≤33 kg 15 mg/kg 60 mg/kg (not exceeding 2 g)
>33 kg to ≤50 kg 15 mg/kg 60 mg/kg (not exceeding 3 g)
>50 kg with additional risk factors for hepatotoxicity 1g 3 g
>50 kg with no additional risk factors for hepatotoxicity 1g 4 g

Special precaution must be observed for patients with hepatocellular insufficiency. The maximum dose per day should not exceed 3g.

Secreted T4 and T3 circulate in the bloodstream almost entirely bound to proteins. Normally only about 0.03% of total plasma T4 and 0.3% of total plasma T3 exist in the free state. Free T3 is biologically active and mediates the effects of thyroid hormone on peripheral tissues in addition to exerting negative feedback on the pituitary and hypothalamus. The major binding protein is thyroxine-binding globulin (TBG), which is synthesized in the liver and binds one molecule of T4 or T3. About 70% of circulating T4 and T3 is bound to TBGl 10% to 15% is bound to another specific thyroid-binding protein called transthyretin (TTR). Albumin binds 15% to 20%, and 3% to lipoproteins. Ordinarily only alterations in TBG concentration significantly affect total plasma T4 and T3 levels.

Two important biological functions have been ascribed to TBG. First, it maintains a large circulating reservoir of T4 that buffers any acute changes in thyroid gland function. Second, binding of plasma T4 and T3 to proteins prevents loss of these relatively small hormone molecules in urine and thereby helps conserve iodide. TTR transports T4 in CSF and provides thyroid hormones to the CNS.

Oxygen consumption (VO2) refers to the optimal amount of oxygen used by the body during exercise.

It is calculated mathematically by:

VO2 = 3.5 x 50 x 8 = 1400 mL/kg/minute

where,

1 MET = 3.5 mL O2/kg/minute is utilized by the body.

Note:

1 MET Eating
Dressing
Use toilet
Walking slowly on level ground at 2-3 mph
2 METs Playing a musical instrument
Walking indoors around house
Light housework
4 METs Climbing a flight of stairs
Walking up hill
Running a short distance
Heavy housework, scrubbing floors, moving heavy furniture
Walking on level ground at 4 mph
Recreational activity, e.g. golf, bowling, dancing, tennis
6 METs Leisurely swimming
Leisurely cycling along the flat (8-10 mph)
8 METs Cycling along the flat (10-14 mph)
Basketball game
10 METs Moderate to hard swimming
Competitive football
Fast cycling (14-16 mph)

The superior laryngeal nerve gives off two branches: the sensory branch which is the internal laryngeal nerve, and the motor branch which is the external laryngeal nerve.

The recurrent laryngeal nerve (RLN) rises from the vagus nerve which supplies the intrinsic muscles of the larynx, except the cricothyroid muscles.

Decreased platelet concentrations with eclampsia were described as early as 1922 by Stancke. The platelet count is routinely measured in women with any form of gestational hypertension. The frequency and intensity of thrombocytopenia vary and are dependent on the severity and duration of the preeclampsia syndrome and the frequency with which platelet counts are performed.

Overt thrombocytopenia defined by a platelet count < 100,000/microliter - indicates severe disease. In general, the lower the platelet count, the higher the rates of maternal and fetal morbidity and mortality. In most cases, delivery is advisable because thrombocytopenia usually continues to worsen. After delivery, the platelet count may continue to decline for the first day or so. It then usually increases progressively to reach a normal level within 3-5 days. In some instances with HELLP syndrome, the platelet count continues to fall after delivery. If these do not reach a nadir until 48 to 72 hours, then preeclampsia syndrome may be incorrectly attributed to one of the thrombotic microangiopathies. The following are other severe features associated with preeclampsia: Proteinuria: >/= 300 mg/24 hours; or urine protein: creatinine ratio >/= 0.3; or dipstick 1+

Renal insufficiency: serum creatinine > 1.1 mg/dL or doubling of creatinine in the absence of other renal disease

Impaired liver function: two times elevated AST/ALT or unexplained right upper quadrant pain or epigastric pain unresponsive to medications

Pulmonary oedema

Cerebral or visual symptoms: headache, visual disturbances

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.

Bupivacaine is used to decrease sensation in a specific area. It is injected around a nerve that supplies the area, or into the spinal canal’s epidural space.

The maximum volume of 0.5% bupivacaine that should be administered to a 10kg child is 5 ml

Giardiasis is known to have a longer incubation time and doesn’t cause bloody diarrhoea.

Cholera usually doesn’t cause bloody diarrhoea.

Generally, most of the E.coli strains do not cause bloody diarrhoea.

Diverticulitis can be a cause of bloody stool but the history here points out to an infectious cause.

Campylobacter infection is the most probable cause as it is characterized by a prodrome, abdominal pain and bloody diarrhoea

Severity of a reduction in restrictive defect (%FVC) or obstructive defect (%FEV1/FVC) predicted are classified as follows:

Mild 70-80%
Moderate 60-69%
Moderately severe 50-59%
Severe 35-49%
Very severe <35% This patient has a mixed deficit with a severe obstructive deficit as %FEV1/FVC predicted is 46.9% and a moderate restrictive deficit as %FVC of predicted is 61.3 FEV1/FVC ratio 80% < predicted and VC < 80% = mixed picture. FEV1/FVC ratio 80% < predicted and VC > 80% = obstructive picture.

FEV1/FVC ratio 80% > predicted and VC > 80% = normal picture.

FEV1/FVC ratio 80% > predicted and VC < 80% predicted= restrictive picture.

The coeliac axis refers to one of the splanchnic arteries located within the abdomen.

It arises from the aorta almost horizontally at the level of the T12 vertebrae

Awareness during general anaesthesia is a frightening experience, which may result in serious emotional injury and post-traumatic stress disorder.

The incidence of awareness during general anaesthesia with current anaesthetic agents and techniques has been reported as 0.2-0.4% in nonobstetric and noncardiac surgery, as 0.4% during caesarean section, and as 1.5% in cardiac surgery.

The incidence during major trauma surgery is higher. Incidence of recall has been reported to be as high as 11-43% in major trauma cases.

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%).

This data is in a 2 × 2 contingency table so a chi square test can be used. There is a special chi squared formula that gives a value that can be looked up in a table giving the p value.

Since we are comparing proportions not means, the Student’s t test CANNOT be used.

There is no linear regression to plot so Pearson’s co-efficient cannot be calculated.

Nothing is so obvious that no statistical analysis is needed.

Lorazepam is an intermediate-acting benzodiazepine that binds to the GABA-A receptor subunit to increase the frequency of chloride channel opening and cause membrane hyperpolarization.

Lorazepam has emerged as the preferred benzodiazepine for acute management of status epilepticus. Lorazepam differs from diazepam in two important respects. It is less lipid-soluble than diazepam, with a distribution half-life of two to three hours versus 15 minutes for diazepam. Therefore, it should have a longer duration of clinical effect. Lorazepam also binds the GABAergic receptor more tightly than diazepam, resulting in a longer duration of action. The anticonvulsant effects of lorazepam last six to 12 hours, and the typical dose ranges from 4 to 8 mg. This agent also has a broad spectrum of efficacy, terminating seizures in 75-80% of cases. Its adverse effects are identical to those of diazepam. Thus, lorazepam also is an effective choice for acute seizure management, with the added possibility of a longer duration of action than diazepam.

Phenobarbitone is a long-acting barbiturate that binds to GABA-A receptor site and increase the duration of chloride channel opening. It also blocks glutamic acid neurotransmission, and, at high doses, can block sodium channels. It is considered as the drug of choice for seizures in infants.

Phenytoin is an anti-seizure drug that blocks voltage-gated sodium channels. It is preferred in prolonged therapy of status epilepticus because it is less sedating.

In cases wherein airway protection is required, thiopentone and propofol are the preferred drugs.

Blood vessels (except capillaries and venules) have three distinctive layers (innermost to outermost):
1. Tunica intima
2. Tunica media
3. Tunica adventitia

The tunica media contains smooth muscle cells and is separated from the intima layer by the internal elastic lamina and the adventitia by the external elastic lamina.

Selection bias is when randomisation is not achieved and is often a result of in efficient recruiting method.

Recall bias is specifically appropriate to the case control studies that is when ever the memories retrieved by the participants differ in accuracy.

Measurement bias can be characterized by gathering of information in a manner that is distorted.

When the participants of a research study are recruited from the hospitals rather than the general population, its called Berkson Bias.

Confounding bias is the major player here because in this case the effects of smoking can be masked behind and can be read as outcomes of lower socio economic status. This extraneous factor (Smoking), distorts the founding.

Lesser the potency of the drug, the higher the dose required to produce maximal receptor occupation. So, the least potent drug will have a log dose-response curve furthest to the right on X-axis.

Based on the option given, tramadol is the least potent drug and thus higher dose is required to produce maximal opioid receptor occupation.

Thus, Tramadol is the least potent opioid with a log dose-response curve furthest to the right on X-axis.

Note, Fentanyl is the most potent opioid with a log dose-response curve furthest to the left on the X-axis.

Adenosine is the first line for AV nodal re-entry tachycardia. An initial dose of 6 mg is given, and a consequent second dose or third dose of 12 mg is administered if the initial dose fails to terminate the arrhythmia.

Aside from Adenosine, a vagal manoeuvre (e.g. carotid massage) is done to help terminate the supraventricular arrhythmia.

Amiodarone is not a first-line drug for supraventricular tachycardias. Digoxin and Propranolol can be considered if the arrhythmia is of a narrow complex irregular type. Verapamil is an alternative to Adenosine if the latter is contraindicated.

This is a classical case of unstable angina or NSTEMI (Non-ST-elevation myocardial infarction). As soon as the diagnosis of unstable angina or NSTEMI is made the initial treatment is Aspirin and antithrombin therapy.

Betablocker is known to reduce mortality from acute myocardial infarction by reducing oxygen demand. If there is no contraindication (heart block, bradycardia, hypotension, severe left ventricular dysfunction, and asthma), a beta-blocker should be given early. This patient has hypotension and therefore metoprolol is contraindicated.

If three doses of nitroglycerine tablets or Nitrolingual sprays and intravenous beta-blockers too cannot relieve the symptoms intravenous Glyceryl Trinitrate (GTN) should be considered provided that there is no hypotension. But in this case, the patient is hypotensive, and therefore, it is contraindicated.

If the symptoms are not relieved after three serial doses of nitroglycerine or if symptoms recur despite adequate anti-anginal treatment morphine sulphate is indicated.

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

The option that is most responsible is the progressive decrease in venous return of blood to the right atrium. The heart rate does not usually change with PEEP so the fall in cardiac output is due to a reduction in left ventricular (LV) stroke volume (SV).

Note that the interventricular septum does shift toward the left and there is an increased pulmonary vascular resistance (PVR) from overdistention of alveolar air sacs that contribute to the reduction in cardiac output. Any increase in PVR will be associated with reduced pulmonary vascular capacitance.

The ureter starts from the hilum of the kidney and has different relations with structures along its journey to the bladder.
It runs anterior to the psoas major muscle.
The testicular vessels (males) or the ovarian vessels (females) cross in front of the ureter.
The ureter passes in front of the common iliac artery where it bifurcates into the internal and external iliac arteries.
The ureter passes medial to the branches of the internal iliac vessel downwards and forwards to towards the bladder.
In males, the ductus deferens crosses the pelvic ureter medially.
In females. the ureter passes through the base of the broad ligament
In females, the pelvic part initially has the same relations as in males but, anterior to the internal iliac artery, it is immediately behind the ovary, forming the posterior boundary of the ovarian fossa. It is in extraperitoneal connective tissue in the inferomedial part of the broad ligament of the uterus. In the broad ligament, the uterine artery is anterosuperior to the ureter for approximately 2.5 cm and then crosses to its medial side to ascend alongside the uterus. The ureter turns forwards slightly above the lateral vaginal fornix and is, generally, 2 cm lateral to the supravaginal part of the uterine cervix in this location. It then inclines medially to reach the bladder.

Endotoxins are the lipopolysaccharides found in the outer cell wall of Gram-negative bacteria. They are responsible for providing the structure and stability of the cell wall.

They cannot be destroyed by normal sterilisation as they are heat stable molecules. They require the use of certain sterilant such as superoxide, peroxide and hypochlorite to be neutralised.

They stimulate strong immune responses, but can only be destroyed partially by specific antibodies. Repeat infections occur as memory T cells cannot be formed.

It can cause septicaemia and associated symptoms such as fever, shock, hypotension and nausea.

It activates the alternative complement pathway and the coagulation pathway using secreted cytokines.

It is not involved in botulism as clostridium botulinum, the responsible organism, secretes a neurotoxic exotoxin.

A is correct. Common myeloid progenitor cells are involved in the anaphylaxis reaction.
B is incorrect. The common lymphoid lineage gives rise to T-cells, B-cell and NK cells.
C is incorrect as megakaryocytes give rise to platelets.
D is incorrect – Neural crest cells give rise to various cells throughout the body, including melanocytes, enterochromaffin cells and Schwann cells. However, they do not give rise to mast cells.
E is incorrect. Reticulocytes give rise to erythrocytes.

This is a classic case of anaphylaxis. In this situation, IgE previously raised against antigens (in this case peanut antigen) bind to mast cells, and this causes them to degranulate.
There is release of vasoactive substances like histamine into the blood, and this is responsible for the symptoms seen. Therefore, the main type of cells involved in the pathogenesis of the disease is mast cells.

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.

The measure of drug potency or therapeutic response is the ED95. This is defined as the dose of a neuromuscular blocking drug required to produce a 95% depression of muscle twitch height. The ED50 and ED90 describe a depression of twitch height by 50% and 90% respectively.

The ED95 (mg/kg) of the commonly used neuromuscular blocking agents are:

suxamethonium: 0.27
rocuronium: 0.31
vecuronium: 0.04
pancuronium: 0.07
cisatracurium: 0.04
mivacurium: 0.08

Chest compressions are an essential part of cardiopulmonary resuscitation (CPR) which helps restore spontaneous circulation (ROSC).

Sodium bicarbonate is only prescribed in patients with cardiac arrests as a result of an overdose of tricyclic antidepressants or hyperkalaemia. Its use causes the body to produce more CO2 which causes:

Exacerbation of intracellular acidosis
Negative inotropy to ischaemic myocardium
Increased osmotic load of sodium into failing brain and body
Shift of oxygen dissociation curve to the left.

THAM is often used to treat metabolic acidosis as a result of cardiac bypass surgery and also cardiac arrest, when other standard methods have failed.

Carbicarb (Na2CO3 0.33 molar NaHCO3 0.33 molar) has only mild effects on acidosis. It also causes an increase in arterial CO2 pressure and lactate concentration.

The patient in the case has a fluid volume requirement of 30 mL/kg/day. His basic electrolyte requirement per day is:

Sodium at 2 mmol/kg/day x 110 = 220 mmol/day
Potassium at 1 mmol/kg/day x 110 = 110 mmol/day

His energy requirement per day is:

35 kcal/kg/day x 110 kg = 3850 kcal/day

One gram of glucose in fluid can provide approximately 4 kilocalories.

The following are the electrolyte components of the different intravenous fluids:

Fluid Na (mmol/L) K (mmol/L)
0.9% Normal saline (NSS) 154 0
0.45% NSS + 5% dextrose 77 0
0.18% NSS + 4% dextrose 30 0
Hartmann’s 131 5
5% dextrose 0 0

1000 mL of 5% dextrose has 50 g of glucose

Option B is inadequate for his sodium and caloric requirements (30 mmol of Na+ and 560 kcal). It is adequate for his K+ requirement (120 mmol of K+).

Option C is in excess of his Na+ requirement (462 mmol of Na+). Moreover, it does not provide any K+ replacement.

Option D is inadequate for his caloric requirement (600 kcal) and K+ requirement (60 mmol of K+). Moreover it does not provide any Na+ replacement.

Option E is in excess of his Na+ requirement (393 mmol of Na+), and is inadequate for his potassium requirement (15 mmol of K+)

Option A has adequate amounts for his Na+ (231 mmol of Na+) and K+ (120 mmol of K+) requirements. It is inadequate for his caloric requirement (600 kcal).

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 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

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 popliteal fossa is the shallow, diamond-shaped depression located in the back of the knee joint.

The structures that lie within in from superficial to deep are:

The tibial and common fibular nerve: Most superficial. They arise from the sciatic nerve.
The popliteal vein
The popliteal artery: Lies deepest. It arises from the femoral artery

Boundaries of the popliteal fossa:

Laterally
Biceps femoris above, lateral head of gastrocnemius and plantaris below

Medially
Semimembranosus and semitendinosus above, medial head of gastrocnemius below

Floor
Popliteal surface of the femur, posterior ligament of knee joint and popliteus muscle

Roof
Superficial and deep fascia

The small and large intestinal walls are composed of the following common layers:
1. Mucosa
2. Submucosa
3. Muscularis Externa
4. Adventitia

Intestinal villi are highly vascular projections of the mucosal surface that cover the entire small intestinal mucosa. They increase the lumen’s surface area, which aids in absorption and digestion, the primary functions of the small intestine. Villi are large and most abundant in the duodenum and jejunum.

In both the small and large intestines, the muscularis mucosae are found within the mucosa. The myenteric nerve plexus is found innervating the muscularis externa. The mucosa is lined with columnar epithelial cells, and goblet cells may be present to secrete mucins.

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.

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 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

The elimination of phenytoin follows first order kinetics. Plasma concentrations determine the rate of elimination. The relationship between drug X plasma concentration and time is described by an exponential process in the following equation used to describe the rate of elimination:

C = C0. e-kt

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

As enzyme systems become saturated when phenytoin concentrations are above the usual range, clearance of the medication becomes zero-order. The medication is metabolised at a constant pace, regardless of its plasma levels. Aspirin and ethyl alcohol are two more significant examples of medications that operate in this way.

A plot of drug concentration with time is a washout exponential curve.

A graph of concentration with time is a straight line i.e. Zero-order kinetics

The amount eliminated per unit time is constant defines the point at which zero order kinetics commences.

Elimination involves a rate-limiting reaction operating at its maximal velocity is incorrect.

The half life of the drug is proportional to the drug concentration in the plasma corresponds to a definition of first-order kinetics.

The metabolism of drugs in the liver occurs in 3 phases

Phase I: This involves functionalization reactions, which are of 3 types, namely hydrolysis, oxidation and reduction reactions catalysed by the cytochrome P450 (CYP) enzymes.

Phase II: This involves conjugation or acetylation reactions. The goal is to create water soluble metabolites that can be excreted from the body.

The liver is the second largest organ. It’s smallest functional unit is the acinus which is divided into 3 zones:

Zone I (periportal): This zone receives the largest amount of oxygen supply as it is the closest to the blood vessels. It is the site of plasma protein synthesis.

Zone II (mediolobular): This is located between the portal triad and central vein.

Zone III (centrilobular): This is closest to the central vein and receives the least amount of oxygen supply.

Kupffer cells are specialized macrophages found in the periportal zone of the liver, and function to remove foreign particles and breakdown red blood cells via phagocytosis.

Ito cells are fat-storing liver cells found in the space of Disse. Their function is to take-uo, store and secrete retinoids, as well as manufacture and release proteins that make up the extracellular matrix.

The leading cause of perioperative anaphylaxis in the UK currently are antibiotics. They account for 46% of cases with identified causative agents. Co-amoxiclav and teicoplanin between them account for 89% of antibiotic-induced perioperative anaphylaxis

Neuromuscular blocking agents (NMBAs) are the second leading cause and account for 33% of case.

Chlorhexidine (0.78/100,000 administrations)
Co-amoxiclav (8.7/100,000 administrations)Suxamethonium (11.1/100,000 administrations)
Patent blue dye (14.6/100,000 administrations)
Teicoplanin (16.4/100,000 administrations)

Anaphylaxis to chlorhexidine periop poses a significant risk in the healthcare setting because of its widespread use with some being fatal.

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

Nitric oxide is generated from L-arginine by nitric oxide synthase. It is produced in response to haemodynamic stress by the vascular endothelium, and it produces both smooth muscle relaxation and reduced vascular resistance.

Nitric oxide may be inactivated through interaction with other oxygen free radicals, (e.g. oxidised low-density lipoprotein (LDL)).

Nitric oxide causes the production of the second messenger, cyclic guanosine monophosphate (cGMP).

Spirometry measures the total volume of air that can be forced out in one maximum breath, that is the total lung capacity (TLC), to maximal expiration, that is the residual volume (RV).

It is conducted using a spirometer which is capable of measuring lung volumes using techniques of dilution.

During spirometry, the following measurements can be determined:
Forced vital capacity (FVC)/vital capacity (VC): The maximum volume of air exhaled in one single forced breathe.
Forced expiratory volume in one second (FEV1)
FEV1/FVC ratio
Peak expiratory flow (PEF): the maximum amount of air flow exhaled in one blow.
Forced expiratory flow (mid expiratory flow): the flow at 25%, 50% and 75% of FVC
Inspiratory vital capacity (IVC): The maximum volume of air inhaled after a full total expiration.

Anatomical dead space is measured using a single breath nitrogen washout called the Fowler’s method.

Residual volume and total lung capacity are both measured using the body plethysmograph or helium dilution

The functional residual capacity is usually measured using a nitrogen washout or the helium dilution technique.

The inguinal triangle of Hesselbach’s 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 inflow of blood from the superior vena cava is directed towards the right atrioventricular orifice. It returns deoxygenated blood from all structures superior to the diaphragm, except the lungs and heart.

There are no valves in the superior vena cava which is why it is relatively easy to insert a CVP line from the internal jugular vein into the right atrium. The brachiocephalic vein is similar as it also has no valves.

PaCO2 is one of the most important factors that regulate cerebral vascular tone. CO2 induces cerebral vasodilatation and as a result, it increases CBF. Between 20 mmHg (2.7 kPa) and 80 mmHg (10.7 kPa), there is a linear increase of PaCO2.

Sometimes, there are areas where auto regulation has failed locally but not globally. Similarly, local vs. systemic acidosis will have similar effects. When the PaO2 falls below 50 mmHg (6.5 kPa), the CBF progressively increases.

An increase in the cerebral metabolic rate for oxygen (CMRO2) and therefore CBF can be caused by hyperthermia.
A late feature of cerebral injury is hyperthermia secondary to hypothalamic injury. Therefore this is not the most likely cause of an increased CBF in this scenario.

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 posterior cerebral arteries are the terminal branches of the basilar artery and are connected to the circle of Willis via the posterior communicating artery. The posterior cerebral artery supplies the visual areas of the cerebral cortex and other structures in the visual pathway.

The posterior cerebral artery is separated from the superior cerebellar artery near its origin by the oculomotor nerve (3rd cranial nerve) and, lateral to the midbrain, by the trochlear nerve.

PCA strokes will primarily cause a visual field loss or homonymous hemianopia to the opposite side. This large occipital or PCA stroke causes people to be “blind” on one side of the visual field. This is the most common symptom of a large occipital lesion or PCA stroke.

The total body water content of a 70kg man is (70 × 0.6) = 42 litres. For a woman, the calculation is (70 × 0.55) = 38.5 litres.

For a man, it is subdivided into:

Extracellular fluid (ECF) = 14L (1/3)
Intracellular fluid (ICF) = 28L (2/3).

The ECF volume is further divided into:

Interstitial fluid = 10.5 litres
Plasma = 3 litres
Transcellular fluid (CSF/synovial fluid) = 0.5 litres.

Directly measured fluid compartments:

Heavy water (deuterium) can be used to measure total body water content, which is freely distributed.
Albumin labelled with a radioactive isotope or using a dye called Evans blue can be used to measure Plasma volume . They do not diffuse into red blood cells.
Radiolabelled (Cr-51) red blood cells can be used to measure total erythrocyte volume.
Inulin as the tracer can be used to measure ECF volume as it circulate freely in the interstitial and plasma volumes.

Indirectly measured fluid compartments:

Total blood volume can be calculated with the level of haematocrit and the volume of total circulating red blood cells.
ICF volume can be calculated by subtracting ECF volume from total blood volume.

Adequate humidification is vital to maintain homeostasis of the airway. Heat and moisture exchangers conserve some of the exhaled water, heat and return them to inspired gases. Many heat and moisture exchangers also perform bacterial/viral filtration and prevent inhalation of small particles. Heat and moisture exchangers are also called condenser humidifier, artificial nose, etc. Most of them are disposable devices with exchanging medium enclosed in a plastic housing. For adult and paediatric age group different dead space types are available. Heat and moisture exchangers are helpful during anaesthesia and ventilatory breathing system. To reduce the damage of the upper respiratory tract through cooling and dehydration inspiratory air can be heated and humidified, thus preventing the serious complications. Moreover, they are the most appropriate humidification devices used for routine anaesthesia.

Gases can be bubbled through water to increase humidity. Passing gas through water at room temperature causes the gas to cool due to latent heat of vaporisation. The water bath can be heated. This improves the efficiency of the device and also reduces the incidence of bacterial colonisation.

Nebulisers use a venturi system which employs the Bernoulli effect. A gas at high flow passes through a constriction causing the gas to accelerate, reducing its potential energy allowing other gases or liquids to be entrained. This can include medications or in the case of humidification, water vapour. The size of the water droplet produced by nebulisation determines where in the airway it is deposited. Standard nebulisers produced droplets of 4 microns in diameter and these are deposited in the upper airway and trachea. Efficacy can be improved by passing the droplets over an anvil which further reduces particle size. The most efficient form of nebuliser is the ultrasonic nebuliser. Here a transducer immersed in water and vibrated at a frequency of 3MHz produces1-2micron droplets. These particles easily reach the bronchioles and provide excellent humidification.

The sinoatrial node receives innervation from multiple nerves arising from the complex cardiac plexus.

The cardiac plexus sends tiny branches into cardiac vessels, alongside the right and left coronary arteries.

The vagal efferent fibres originate from the vagal and accessory nerves in the brainstem, and then travel to the cardiac plexus within the heart. The resulting vagal discharge controls heart rate.

No singular nerve directly innervates the sinoatrial node.

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.

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)

The diaphragm divides the thoracic cavity from the abdominal cavity. Structures penetrate the diaphragm at different vertebral levels through openings in the diaphragm to communicate between the two cavities. The diaphragm has openings at three vertebral levels:

T8: vena cava, terminal branches of the right phrenic nerve
T10: oesophagus, vagal trunks, left anterior phrenic vessels, oesophageal branches of the left gastric vessels
T12: descending aorta, thoracic duct, azygous and hemi-azygous vein

The left gastric artery is the smallest branch that originates from the coeliac trunk—the coeliac trunk branches of the abdominal aorta at the vertebral level of T12.

The left gastric artery runs along the superior portion of the lesser curvature of the stomach. A peptic ulcer that is serious enough to erode through the stomach mucosa into a branch of the left gastric artery can cause massive blood loss in the stomach, leading to hematemesis. The patient also takes Naproxen, a non-steroidal anti-inflammatory drug that is a common cause for peptic ulcers in otherwise healthy patients.

The left gastric artery is responsible for 85% of upper GI bleeds. In cases refractory to initial treatment, angiography is sometimes needed to embolise the vessel at its origin and stop bleeding. During an angiogram, the radiologist will enter the aorta via the femoral artery, ascend to the level of the 12th vertebrae and then enter the left gastric artery via the coeliac trunk.

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

When a drug is given via intravenous infusion, the plasma concentration rises exponentially as a wash-in curve until it reaches steady-state concentration (the point at which the infusion rate is balanced by the elimination rate or clearance). To reach this steady state, the drug will take 4-5 half-lives.

Cpss (target plasma concentration at steady state) and clearance (CL) in ml/minute or litre/hour are the two factors that determine the infusion rate or dose (ID) in mg/hour of a drug.

ID = Cpss × CL

We know the infusion rate is 20 ml/hour in this case. The drug’s concentration is 5 mg/mL. The patient is receiving 100 mg of the drug per hour, with a 20 L/hour clearance rate.

ID = Cpss × 20

Therefore,

Cpss = 100 mg/20000 ml

Cpss = 0.005 mg/mL or 5 mcg/mL

The cephalic vein is a superficial vein that runs through the forearm and the arm, before draining into the axillary vein where it terminates.

Phase I and phase II metabolism are used by the liver to break down paracetamol.

1st Phase:

Prostaglandin synthetase and cytochrome P450 (CYP1A2, CYP2E2, CYP3A4 and CYP2D6) to N-acetyl-p-benzoquinoneimine (NAPQI) and N-acetylbenzo-semiquinoneimine. NAPQI is a toxic metabolite that binds to the sulfhydryl groups of cellular proteins in hepatocytes, making it toxic. This can result in centrilobular necrosis.

Glutathione and glutathione transferases prevent NAPQI from binding to hepatocytes at low paracetamol doses by preferentially binding to these toxic metabolites. The cysteine and mercapturic acid conjugates are then excreted in the urine. Depletion of glutathione occurs at higher doses of paracetamol, resulting in high levels of NAPQI and the risk of hepatocellular damage. Hepatotoxicity would not be an issue if the body’s glutathione stores were sufficient.

N-acetylcysteine is a precursor for glutathione synthesis and is the drug of choice for the treatment of paracetamol overdose.

Phase II:

Conjugation with glucuronic acid to paracetamol glucuronide is the most common method of metabolism and excretion, accounting for 60% of renally excreted metabolites. Paracetamol sulphate (35%), unchanged paracetamol (5%), and mercapturic acid are among the other renally excreted metabolites (3 percent ). The capacity of conjugation pathways is limited. The capacity of the sulphate conjugation pathway is lower than that of the glucuronidation pathway.

Because of the low pH in the stomach, paracetamol absorption is minimal (pKa value is 9.5). Paracetamol is absorbed quickly and completely in the alkaline environment of the small intestine. Oral bioavailability is extremely high, approaching 100%.

As a result, measuring paracetamol levels in plasma after an injury is important. Peak plasma concentrations are reached after 30-60 minutes, with a volume of distribution of 0.95 L/kg. It binds to plasma proteins at a rate of 10% to 25%.

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.

The left coronary artery arises from the left posterior aortic sinus and divides into the circumflex arteries and the left anterior descending (LAD) artery.

The right coronary artery arises from the anterior aortic sinus and supplies:
– the right ventricle
– part of the interventricular septum
– the atrioventricular (A-V) node and
– in 85% of cases the inferior part of the left ventricle.
The right coronary artery provides a posterior interventricular branch and a marginal branch that anastomoses with the LAD at the apex.

The oblique vein together with the small, middle and great cardiac veins drain into the coronary sinus, which drains into the right atrium.

The anterior cardiac vein drains directly into the right atrium.

Creatinine clearance is a test used to approximate the glomerular filtration rate (GFR) as an assessment of kidney function.

Creatinine is formed during the breakdown of dietary sources of meat and skeletal muscle. It is secreted at a consistent concentration and pace into the body’s circulation, and is easily filtered across the glomerulus without being reabsorbed or metabolized by the kidney.

It is represented mathematically as:
Creatinine clearance (CL) = U x V/P
where,
U: Urinary creatinine concentration (mg/mL)
V: Volume of urine (mL/min)
P: Plasma creatinine concentration (mg/mL)

Therefore, in this case:
CL: 1.25 x 1 = 125mL/min
0.1

Capnography is the non-invasive measurement and pictorial display of inhaled and exhaled carbon dioxide (CO2) partial pressure.

It is depicted graphically as the concentration of CO2 over time.

It is used in disease diagnosis, determining disease severity, assessing response to treatment and is the best method to for indicating when an endotracheal tube is placed in the trachea after intubation.

The wavelength of IR light usually absorbed by nitrous oxide is between 4.4-4.6?m (very close to that of CO2). Its absorption of wavelengths at 3.9 ?m is much weaker. It causes a measurable deficit of 0.1% for every 10% of nitrous oxide. The maximal wavelength of infrared (IR) light absorbed by carbon monoxide is 4.7 ?m. The volatile agents have strong absorption bands at 3.3 ?m and throughout the ranges 8-12 ?m.

IR light is not absorbed by oxygen (O2), but O2 and CO2 molecules are constantly colliding which interrupts the absorption of IR light by CO2. This increases the band of absorption, that is the Collison or pressure broadening). An oxygen percentage of 95 will result in a 0.5 percentage fall in CO2 measure.

IR light is also absorbed by water vapour which will result in an overlap of the absorption band, collision broadening and a dilution of partial pressure. This is why water trap and water permeable tubing is recommended for use as it reduces measurement inaccuracies.

The use of multi-gas analysers of modern gases also help reduce the effects of collision broadening.

Beer’s law is also applied in this system as an increase in the concentrations of CO2 causes a decrease in the amount of IR able to pass through the gas. This IR light is what generated the signal that is analysed for display.

The capnograph can indicate oesophageal intubation, but cannot determine if it is endotracheal or endobronchial. For this, auscultation is used.

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 ‘ideal’ alveolar PO2 minus arterial PO2 is the alveolar-arterial (A-a) oxygen difference.

The ‘ideal’ alveolar PO2 is derived from the alveolar air equation and is the PO2 that the lung would have if there was no ventilation-perfusion (V/Q) inequality and it was exchanging gas at the same respiratory exchange ratio as real lung.

The amount of oxygen in the blood is measured directly in the arteries.

The A-a oxygen difference (or gradient) is a useful measure of shunt and V/Q mismatch, and it is less than 2 kPa in normal adults breathing air (15 mmHg). Because the shunt component is not corrected, the A-a difference increases when breathing 100 percent oxygen, and it can be up to 15 kPa (115 mmHg).

An abnormally low or abnormally high V/Q ratio within the lung can cause an increased A-a difference, though the former is more common. Atelectasis, which results in a low V/Q ratio, is the most likely cause of an A-a difference in a healthy adult breathing 100 percent oxygen.

Hypoventilation may cause an increase in alveolar (and thus arterial) CO2, lowering alveolar PO2 according to the alveolar air equation.

The alveolar PO2 is also reduced at high altitude.

Healthy people are unlikely to have a right-to-left shunt or an oxygen transport diffusion defect.

ARR= (Risk factor associated with the new drug group) — (Risk factor associated with the currently available drug)

So,

ARR= (10/400)-(20/400)

ARR= 0.025-0.05

ARR= 0.025 (Numerical Value)

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.

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.

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 Mapleson A (Magill) and coaxial version of the Mapleson A system (Lack circuit) are more efficient for spontaneous breathing than any of the other Mapleson circuits. The fresh gas flow (FGF) required to prevent rebreathing is slightly greater than the alveolar minute ventilation (4-5 litres/minute). This is delivered to the patient through the outer coaxial tube and exhaust gases are moved to the scavenging system through the inner tube. In the Lack circuit, the expiratory valve is located close to the common gas outlet away from the patient end. This is the main advantage of the Lack circuit over the Mapleson A circuit.

The Mapleson E circuit is a modification of the Ayres T piece and the FGF required to prevent rebreathing is 1.5-2 times the patient’s minute volume.

The Bain circuit is the coaxial version of the Mapleson D circuit.

The FGF for spontaneous respiration to avoid rebreathing is 160-200 ml/kg/minute.

The FGF for controlled ventilation to avoid rebreathing is 70-100 ml/kg/min.

Atrial natriuretic peptide (ANP) is secreted mainly from myocytes of right atrium and ventricle in response to increased blood volume.
It is secreted by both the right and left atria (right >> left).

It is a 28 amino acid peptide hormone, which acts via cGMP
degraded by endopeptidases.

It serves to promote the excretion of sodium, lowers blood pressure, and antagonise the actions of angiotensin II and aldosterone.

Low molecular weight heparin (LMWH) creates a complex by binding to antithrombin. This complex binds with and inactivates factor Xa.

There is less risk of bleeding with LMWH because it binds less to platelets, endothelium and von Willebrand factor.

LMW binds Xa more readily. The shorter chains are less likely to bind both antithrombin and thrombin.

There is need for monitoring in renal impairment because LMHW is excreted in the urine (and partly by hepatic metabolism)

LMWH have been shown to be as efficacious as unfractionated heparin. It is also safer and have improved inpatient stay and reduced hospital cost.

This patient has been shifted to a sulfonylurea drug whose most common side effect is hypoglycaemia. Similar symptoms can arise in a patient on insulin too. The signs and symptoms are consistent with a hypoglycaemic attack and include tachycardia, altered consciousness, and behaviour. This needs to be treated as an emergency with rapid correction of the blood glucose level using glucose or IV 20% dextrose.

In a hypoglycaemic attack, the body undergoes stress and releases hormones to increase blood glucose levels. These include:
Glucagon
Cortisol
Adrenaline

Adrenaline or epinephrine is the hormone responsible for this patient’s condition and is primarily produced in the medulla of the adrenal gland. It functions primarily to raise cardiac output and raise blood glucose levels in the blood.

Alpha-cells of the islets of Langerhans produce the hormone glucagon, which has opposing effects to insulin.

Follicular cells of the thyroid gland produce and secrete thyroid hormones. Thyroid hormones can cause similar symptoms, but it is unlikely with the patient’s medical history.

Post-ganglionic neurons of the sympathetic nervous system use norepinephrine as a neurotransmitter. Adrenaline can be made in these cells, but it is not their primary production site.

Zona fasciculata of the adrenal cortex is the main site for the production of cortisol.

The incidence of a disease is the number of new cases of the disease in a population over a defined time period.

The prevalence of a disease is the number of cases of the disease in a population over a defined time period describes. It is NOT the number of new cases.

The number of new cases of a disease only, has no denominator (time period or population) from which to derive an incidence.

The number of new cases of a disease seeking medical treatment is the incidence of patients seeking medical treatment NOT the incidence of the disease in a population.

The death rate from a disease is the number of patients dying from the disease in a population.

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.

Salmeterol is a long-acting Beta 2 selective agonist. Therefore it is only used for prophylaxis whereas salbutamol is a short-acting Beta 2 agonist and is thus used for the treatment of acute attacks of asthma.

Salmeterol is 15 times more potent than salbutamol at the Beta 2 receptor but 4 times less potent at the Beta 1 receptor.

Tachyphylaxis to the unwanted side effects commonly occurs, but not to bronchodilation.

Skeletal muscle blood flow is in the range of 1-4 ml/min per 100 g when at rest. Blood flow can reach 50-100 ml/min per 100 g during exercise. With maximal vasodilation, blood flow can increase 20 to 50 times.

The adrenal medulla releases catecholamines and increases neural sympathetic activity during exercise. Normally, alpha-1 and alpha-2 would cause vasoconstriction in the muscle groups being used, but vasodilatory metabolites override these effects, resulting in a so-called functional sympathectomy. Local hypoxia and hypercarbia, nitric oxide, K+ ions, adenosine, and lactate are some of the stimuli that cause vasodilation.

However, the splanchnic and cutaneous circulations, which supply inactive muscles, vasoconstrict.

Sympathetic cholinergic innervation of skeletal muscle arteries is found in some species (such as cats and dogs, but not humans). Vasodilation is induced by stimulating smooth muscle beta-2 adrenoreceptors, but at rest, the alpha-adrenoreceptor effects of adrenaline and noradrenaline predominate. During exercise, the skeletal muscle pump promotes venous emptying, but it does not necessarily increase blood flow.

The magnitude of x determines the rate of change of x. First-order drug kinetics is a good example. Most drugs’ plasma levels are controlled by an exponential process. The rate of change in drug metabolism is proportional to the current plasma concentration (so-called non-linear kinetics).

A tear-away function is just one type of exponential relationship (y = ex), in which e is Euler’s number, x is the power, and e is the base. Natural logarithms rely on Euler’s number.

Euler’s number is a mathematical constant, not a mathematical principle. It’s referred to as an irrational number. This is a number that cannot be expressed as a simple fraction or a ratio.

A line or curve that acts as the limit of another line or curve is known as an asymptote. A washout exponential curve, for example, where the value y represents the plasma concentration of a drug in a single compartment model against time on the x axis. This descending curve approaches but never touches the x axis. This curve is asymptotic to the x axis, which is the curve’s asymptote. An asymptote isn’t just a characteristic of exponential curves.

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.

ACTH production is stimulated through the secretion of corticotropin-releasing hormone (CRH) from the hypothalamic nuclei.

ACTH secretion has a circadian rhythm. A high level of cortisol in the body stops its production. ACTH is secreted maximally in the morning and concentrations are lowest at midnight.

ACTH can be expressed in the placenta, the pituitary and other tissues.

Conditions where ACTH concentrations rise include: stress, disease and pregnancy.

Glucocorticoids (not mineralocorticoids – aldosterone) switch off ACTH production through a negative feedback loop .

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%

Tests are used to confirm the presence of a particular disease. However the results can be misleading at times since most of the tests have some limitations associated with them.
Sensitivity is the correct term that refers to the probability of a positive test. The others are explained below:

False Positive rates refer to the proportion of the patients who don’t have the condition being detected as positive.

False Negative rates refer to the proportion of the patients who have the condition being detected as negative (like the 20% of the patients that went undetected by the Ca-125 test).

Specificity describes the ability of a test to detect and pick up people without the disease. Absolute risk ratio compares the rate of two separate outcomes.

Approximately 25% of phase-1 drug reactions is made responsible by CYP2D6.

As much as a 1,000-fold difference in the ability to metabolise drugs by CYP2D6 can happen between phenotypes, and this may result in adverse drug reactions (ADRs).

The metabolism of antiemetics, beta-blockers, codeine, tramadol, oxycodone, hydrocodone, tamoxifen, antidepressants, neuroleptics, and antiarrhythmics is also as a result of CYP2D6.

Patients who take drugs that are metabolised by CYP2D6 but have poor CYP2D6 metabolism are more likely to have ADRs. People with ultra-rapid CYP2D6 metabolism may have a decreased drug effect due to low plasma concentrations of these drugs.

All the other CYP enzymes are subject to genetic polymorphism. Variants are less likely to lead to adverse drug reactions.

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.

According to European Group protocol for the investigation of MH susceptibility, muscle biopsy should be performed on quadriceps muscle (either vastus medialis or vastus lateralis), using regional anaesthesia (avoiding local anaesthetic infiltration) or general anaesthetic techniques. Local anaesthetic solution within muscle fibres may affect in vitro contraction testing.

Desflurane is a weak triggering anaesthetic of malignant hyperthermia so is avoided in MH susceptible patients. This includes all volatile inhalational agents and suxamethonium.

General anaesthetic with the volatile free anaesthetic machine may be considered but spinal anaesthesia is a better choice due to the possibility of airway problems.

The structures that pass through the foramen magnum are:

Meningeal lymphatics
Spinal cord
Spinal meninges
Sympathetic plexus of vertebral arteries
Vertebral arteries
Vertebral artery spinal branches
The spinal roots of the accessory nerve.

The jugular foramen contains the vagus nerve, the accessory nerve and glossopharyngeal nerve.

The vertebral veins does not pass into the skull.