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

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

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

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

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

The international system of units, or system international d’unites (SI) is a collection of measurements derived from expanding the metric system.

There are seven base units, which are:

Metre (m): a unit of length
Second (s): a unit of time
Kilogram (kg): a unit of mass
Ampere (A): a unit of electrical current
Kelvin (K): a unit of thermodynamic temperature
Candela (cd): a unit of luminous intensity
Mole (mol): a unit of substance.

Cell membrane pore formation, Bacterial DNA damage, Peptidoglycan cross-linking inhibition, and peptidoglycan synthesis inhibitor are always lethal and such mechanisms are possible only in bactericidal drugs. But Protein synthesis inhibition would only prevent cell replication or cell growth and is responsible for bacteriostatic effects of the drug.

Perioperative and postoperative analgesia can both be provided by an inguinal hernia field block. The Iliohypogastric and ilioinguinal nerves, as well as the skin, superficial fascia, and deeper structures, must be blocked for maximum effectiveness. The local anaesthetic should ideally have a long duration of action, be highly concentrated, and have a volume of at least 30 mL.

Plain bupivacaine has a maximum safe dose of 2 mg/kg body weight.

Because the patient weighs 75 kg, 150 mg bupivacaine can be safely administered. Both 30 mL 0.5 percent bupivacaine (150 mg) and 60 mL 0.25 percent bupivacaine (150 mg) are acceptable doses, but 30 mL 0.5 percent bupivacaine represents the optimal volume and strength, potentially providing a denser and longer block.

The maximum safe dose of plain lidocaine has been estimated to be between 3.5 and 5 mg/kg. The patient weighs 75 kg and can receive a maximum of 375 mg using the higher dosage regimen:

There are 200 mg of lidocaine in 10 mL of 2% lidocaine (and therefore 11 mL contains 220 mg)
200 mg of lidocaine is contained in 20 mL of 1% lidocaine.

While alternatives are available, Although the doses of 11 mL lidocaine 2% and 20 mL lidocaine 1% are well within the dose limit, the volumes used are insufficient for effective field block for this surgery.

With 1 in 200,000 epinephrine, the maximum safe dose of lidocaine is 7 mg/kg. The patient can be given 525 mg in this case. Even with epinephrine, 60 mL of 1% lidocaine is 600 mg, which could be considered an overdose.

Myoglobin is a haemoglobin-like, iron-containing pigment that is found in muscle fibres. It has a high affinity for oxygen and it consists of a single alpha polypeptide chain. It binds only one oxygen molecule, unlike haemoglobin, which binds 4 oxygen molecules.

The myoglobin ODC is a rectangular hyperbola. There is a very low P50 0.37 kPa (2.75 mmHg). This means that it needs a lower P50 to facilitate oxygen offloading from haemoglobin. It is low enough to be able to offload oxygen onto myoglobin where it is stored. Myoglobin releases its oxygen at the very low PO2 values found inside the mitochondria.

P50 is defined as the affinity of haemoglobin for oxygen: It is the PO2 at which the haemoglobin becomes 50% saturated with oxygen. Normally, the P50 of adult haemoglobin is 3.47 kPa(26 mmHg).

Foetal haemoglobin has 2 ? and 2 ?chains. The ODC is left shifted – this means that P50 lies between 2.34-2.67 kPa [18-20 mmHg]) compared with the adult curve and it has a higher affinity for oxygen. Foetal haemoglobin has no ? chains so this means that there is less binding of 2.3 diphosphoglycerate (2,3 DPG).

Carbon monoxide binds to haemoglobin with an affinity more than 200-fold higher than that of oxygen. This therefore decreases the amount of haemoglobin that is available for oxygen transport. Carbon monoxide binding also increases the affinity of haemoglobin for oxygen, which shifts the oxygen-haemoglobin dissociation curve to the left and thus impedes oxygen unloading in the tissues.

In sickle cell disease, (HbSS) has a P50 of 4.53 kPa(34 mmHg).

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

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

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

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

Sevoflurane is highly fluorinated methyl isopropyl ether widely used as an inhalational anaesthetic. It is suggested that sevoflurane preconditioning occurs via the opening of mitochondrial Potassium ATP dependent channel similar to that of Ischemic Preconditioning protection.

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.

Staphylococcus aureus infection is the most likely cause.

Surgical site infections (SSI) occur when there is a breach in tissue surfaces and allow normal commensals and other pathogens to initiate infection. They are a major cause of morbidity and mortality.

SSI comprise up to 20% of healthcare associated infections and approximately 5% of patients undergoing surgery will develop an SSI as a result.
The organisms are usually derived from the patient’s own body.

Measures that may increase the risk of SSI include:
-Shaving the wound using a single use electrical razor with a disposable head
-Using a non iodine impregnated surgical drape if one is needed
-Tissue hypoxia
-Delayed prophylactic antibiotics administration in tourniquet surgery, patients with a prosthesis or valve, in clean-contaminated surgery of in contaminated surgery.

Measures that may decrease the risk of SSI include:
1. Intraoperatively
– Prepare the skin with alcoholic chlorhexidine (Lowest incidence of SSI)
-Cover surgical site with dressing

In contrast to previous individual RCT’s, a recent meta analysis has confirmed that administration of supplementary oxygen does not reduce the risk of wound infection and wound edge protectors do not appear to confer benefit.

2. Post operatively
Tissue viability advice for management of surgical wounds healing by secondary intention

Use of diathermy for skin incisions
In the NICE guidelines the use of diathermy for skin incisions is not advocated. Several randomised controlled trials have been undertaken and demonstrated no increase in risk of SSI when diathermy is used.

The principle by which a strain gauge works is that when a wire is stretched, it becomes longer and thinner, and as a result, its resistance increases.

A strain gauge, which is used in pressure transducers, acts as a resistor. When the pressure in a pressure transducer changes, the diaphragm moves, changing the tension in the resistance wire and thus changing the resistance.

Changes in current flow through the resistor are amplified and displayed as a pressure change measure.

A Wheatstone bridge, on the other hand, is frequently used to measure or monitor these changes in resistance.

Direct laryngoscopy are performed using laryngoscopes and they can be classed according to the shape of the blade as curved or straight.

Miller, Soper, Wisconsin and Seward are examples of straight blade laryngoscopes. Straight blades are commonly used for intubating neonates and infants but can be used in adults too.

The tip of the miller blade is advanced over the epiglottis to the tracheal entrance then lifted in order to view the vocal cords.

The RIGHT-SIDED Macintosh blade is used in adults while the left-sided blade may be used in conditions that make intubation with standard blade difficult e.g. facial deformities.

The McCoy laryngoscope is based on the STANDARD MACINTOSH blade not Robertshaw’s. It has a lever operated hinged tip, which improves the view during laryngoscopy.

Polio blade is mounted at an angle of 120-135 degrees to the handle. Originally designed for use during the polio epidemic ​in intubation patients within iron lung ventilators, it is now useful in patients with conditions like breast hypertrophy, barrel chest, and restricted neck mobility.

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.

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

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

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

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

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

Oxytocin acts through G protein-coupled receptor and phosphoinositide-calcium second messenger system to contract uterine smooth muscle.

It has 0.5 to 1 % ADH activity introducing possibilities of water intoxication when used in high doses.

The sensitivity of the uterus to oxytocin increases as the pregnancy progresses.

It is used for induction of labour in post maturity and uterine inertia.

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

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

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

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

ANOVA is based upon within group variance (i.e. the variance of the mean of a sample) and between group variance (i.e. the variance between means of different samples). The test works by finding out the ratio of the two variances mentioned above. (Commonly known as F statistic).

The aminosteroid rocuronium is the neuromuscular blocking agent in question.

0.3 mg/kg is the effective dose 95 (ED95) (the dose required to depress the twitch height by 95 percent )
The dose for intubation is 0.6 mg/kg.
75 seconds is the time it takes to reach 95 percent depression of the first twitch of the train of four (ToF) or the onset time.
The clinical duration or time to 25% recovery of the first twitch of the train of four (ToF) is 33 minutes.

A modified cyclodextrin can quickly reverse both rocuronium and vecuronium (sugammadex).

It is more fat-soluble than vecuronium, with the liver absorbing the majority of the drug and excreting it in the bile. The only metabolite found in the blood (17-desacetylrocuronium) is 20 times less potent than the parent drug and is unlikely to cause neuromuscular block.

Despite its quick onset of action (60-90 seconds), suxamethonium arguably is still the neuromuscular blocker of choice for a quick sequence induction. Rocuronium is becoming increasingly popular for this purpose.

The pulse oximeter provides a continuous non-invasive measurement of the arterial oxygen saturation. The light emitting diodes (LEDs) produce beams of red and infrared light at 660 nm and 940 nm respectively (not 640 and 960 nm), which travel through a finger (toe, ear lobe or nose) and are then detected by a sensitive photodetector.

The light absorbed by non-pulsatile tissues is constant (DC), and the non-constant absorption (AC) is the result of arterial blood pulsation. The DC and AC components at 660 and 940 nm are then analysed by the microprocessor and the result is related to the arterial saturation.

An isosbestic point is a point at which two substances absorb a wavelength of light to the same degree. In pulse oximetry the different absorption profiles of oxyhaemoglobin and deoxyhaemoglobin are used to quantify the haemoglobin saturation (in %). Isosbestic points occur at 590 and 805 nm (not 490 and 805 nm), where the light absorbed is independent of the degree of saturation, and are used as reference points.

The pulse oximeter is accurate to within +/- 2% in the range of 70% to 100% saturation, and below 70% the readings are extrapolated. Pulse oximeters average their readings every 10 to 20 seconds and thus they cannot detect acute desaturation events. Consequently, they are often referred to as ‘lag’ monitors, due to the time delay in identifying the desaturation episode.

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.

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.

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

There is no mandibular artery but the first part of the maxillary artery is called the mandibular part as it is posterior to the lateral pterygoid muscle.
The maxillary artery is divided into three portions by its relation to the lateral pterygoid muscle:
first (mandibular) part: posterior to the lateral pterygoid muscle
second (pterygoid or muscular) part: within the lateral pterygoid muscle
third (pterygopalatine) part: anterior to the lateral pterygoid muscle

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

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

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

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

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

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

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 subclavian artery originates from the aortic arch, while the right subclavian artery originates from the brachiocephalic artery.

The subclavian artery gives off branches on both sides of the body:
1. Vertebral artery
2. Internal thoracic artery
3. Thyrocervical trunk
4. Costocervical trunk
5. Dorsal scapular artery

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

The 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

BMR is lower in females than males.

It decreases with increasing age.

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

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

The midgut gives rise to the appendix.
At week 6, the caecal diverticulum appears and is the precursor for the cecum and vermiform appendix. The cecum and appendix undergo rotation and descend into the right lower abdomen. The appendix can take up various positions:
1. Retrocecal appendix: behind the cecum
2. Retrocolic appendix: behind the ascending colon
3. Pelvic appendix: appendix descends into the pelvis

The appendix grows in length so that at birth, it is long and worm-shaped, or vermiform. After birth, the caecal wall grows unequally, and the appendix comes to lie on its medial side.

The midgut develops into the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of the transverse colon.

Staphylococcus aureus colonizes the nasopharynx in >20% of the general population.

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to flucloxacillin.

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

All ?-lactam antibiotics like penicillin interfere with the synthesis of the bacterial cell walls. The ?-lactam antibiotics inhibit the transpeptidases so that cross-linking (which maintains the close-knit structure of the cell wall) does not take place

Since the data is normally distributed, 95.4% of the values lie with in 2 standard deviations from mean. The rest of the 4.6% are distributed symmetrically outside of that range which means 2.3% of the values lie above 2 standard deviations of the mean.

This may be the classical case of blood transfusion reaction due to ABO incompatibility.

Here red cells are destroyed in the bloodstream with the release of haemoglobin in circulation (causing haemoglobinuria). Here, IgM or IgG anti-A or anti-B antibody can cause rapid activation of complement cascade usually the classical pathway. This is called intravascular haemolysis.

There may be extravascular haemolysis by cells of the mononuclear phagocyte system situated in the liver and spleen. Extravascular red cell destruction can increase breakdown products of haemoglobin, such as bilirubin and urobilinogen.

A decrease in the functional residual capacity (FRC) is the most important physiologic change to consider for such patients.

FRC is the sum of the expiratory reserve volume and the residual volume. It is the resting volume of the lung, and is an important marker for lung function. During this time, the alveolar pressure is equal to the atmospheric pressure. When morbidly obese individuals lie supine, the FRC decreases by as much as 40% because the abdominal contents push the diaphragm into the thoracic cavity.

Chest wall compliance is expected to reduce because of fat deposition surrounding adjacent structures.

Inspiratory reserve volume (IRV) is expected to increase, and peak expiratory flow is expected to decrease, however the decrease in FRC is more important to consider because of the risk of hypoxia secondary to premature airway closure and ventilation-perfusion mismatch.

Breathing 100% oxygen for three minutes will provide the best reservoir of oxygen during apnoea by oxygenating the functional residual capacity (FRC).

Sitting at 45 degrees might increase the FRC and improve oxygen reserve but not compared with 100% oxygenation.

The following table compares the oxygen reserves in the body following pre-oxygenation with room air and 100% oxygen:

Compartment Factors Room air (mL) 100% O2 (mL)
Lung FAO2, FRC 630 2850
Plasma PaO2, DF, PV 7 45
Red blood cells Hb, TGV, SaO2 788 805
Myoglobin – 200 200
Interstitial space – 25 160

FAO2 = alveolar fraction of oxygen.
FRC = Functional residual capacity.
PaO2 = partial pressure of oxygen dissolved in arterial blood
DF = dissolved form.
PV = plasma volume.
TG = total globular volume .
Hb = haemoglobin concentration.
SaO2 = arterial oxygen saturation

Stopping smoking one month prior to surgery will not be more effective than pre-oxygenation with 100% oxygen though it may reduce postoperative pulmonary complications. Note that both long term and short term abstinence reduces pulse rate and blood pressure thus reducing oxygen consumption and also reduce carboxyhaemoglobin levels.

Blood transfusion will not make a big difference in oxygen reserve, particularly if a blood transfusion is administered within 12-24-hours before surgery.

Heliox (79% helium and 21% oxygen) despite its lower viscosity is unlikely to be more effective than 100% oxygen .

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).

Serum specific IgE assays against allergen sources/molecules are the most commonly used in vitro diagnostic approach. The measurement of specific IgE recognizing allergenic epitopes can be achieved both through the usage of single reagents (singleplex) or with a pre-defined panel of a number of molecules to be tested simultaneously (multiplex).

Several clinical entities have been described and those occurring immediately after drug exposure are immunoglobulin E (IgE)-mediated and explored by skin testing and by the in vitro measurement of serum-specific IgE. The sensitivity of these tests is not 100% and even for patients with a clear positive history, a drug provocation test may be required in order to confirm the diagnosis. The advantages of the in vitro determination of specific IgE antibodies when compared with in vivo testing are that the former poses no direct risk to the patient and does not require personnel with expertise. Even though in vitro tests are recommended in immediate hypersensitivity reactions, their exact place in the diagnostic procedure is not clear and certain authors do not use this method in daily practice. In one study, in terms of sensitivity, 11 of 26 patients (42%) with negative skin tests and a positive drug provocation challenge (or repeated clinical history) had specific IgE to benzylpenicilloyl or amoxicilloyl (4). The specificity of the test was 95–100%. Therefore, IgE measurements can avoid a potentially harmful drug provocation test.

An elevated serum tryptase does not differentiate between type 1 and type 2 hypersensitivity reaction. It indicates mast cell degranulation.

RAST is a useful aid to improve the overall diagnosis of drug allergies by using radioactive detection. This, however, is now rarely used.

Quantification of basophil activation by CD63 expression can be done by flow cytometry, which forms the basis of experimental drug-induced basophil stimulation tests.

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.

Ketamine, a phencyclidine derivative, is an antagonist at the NMDA receptor. It causes depression of the CNS that is dose dependent and induces a dissociative anaesthetic state with profound analgesia and amnesia.

Ketamine has a chiral centre usually presented as a racemic mixture with two optical isomers, S (+) and R (-) forms. These isomers are in equal proportions. The S (+) isomer is about three times more potent than the R (-) form. The S (+) form is less likely to cause emergence delirium and hallucinations.

Ketamine is extensively metabolised by hepatic microsomal cytochrome P450 enzymes producing norketamine as its main metabolite. Norketamine has a one third to one fifth as potency as its parent compound.
It increases the CMRO2, cerebral blood flow and potentially increase intracranial pressure.

Venous cutdown is a surgical procedure when venous access is difficult, and other procedures like the Seldinger technique, ultrasound-guided venous access, and intraosseous vascular access have failed.

The vein of choice for venous cutdown is the long/great saphenous vein. It is part of the superficial venous collecting system of the lower extremity. It is the preferred vein as the long saphenous vein has anatomic consistency and is superficially located at the ankle anterior to the medial malleolus. It is also the most commonly used conduit for cardiovascular bypass operations.

Origin- in the foot at the confluence of the dorsal vein of the first digit and the dorsal venous arch of the foot
Route- runs ANTERIOR to the medial malleolus and travels up in the medial leg and upper thigh.
Termination: in the femoral vein within the femoral triangle

Regarding the other options:
The short saphenous vein passes posterior to the lateral malleolus.
The dorsalis pedis vein accompanies the dorsalis pedis artery on the anterior foot.
The posterior tibial vein is part of the deep venous system accompanying the posterior tibial artery. There is no significant sural vein (there is a sural nerve), but the sural veins accompany the sural arteries and drain to the popliteal vein.

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

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

Adrenaline acts on ?1, ?2,?1, and ?2 receptors and also on dopamine receptors (D1, D2) and have sympathomimetic effects.

Natural catecholamines are Adrenaline, Noradrenaline, and Dopamine

Adrenaline is a sympathomimetic amine with both alpha and beta-adrenergic stimulating properties.
Adrenaline is the drug of choice for anaphylactic shock
Adrenaline is also used in patients with cardiac arrest. The preferred route is i.v. followed by the intra-osseous and endotracheal route.

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

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

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

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

Lidocaine 1% is formulated as 1000 mg/100 mL.

% solution is based on (grams of medicine) / 100 ml

% solution ~ (1000 mg) / 100 ml

% solution ~ 10 mg/ml

Examples:

• • Lidocaine 4% = 40 mg/ml of Lidocaine
  • Lidocaine 2% = 20 mg/ml of Lidocaine
  • Lidocaine 1% = 10 mg/ml of Lidocaine

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

Lorazepam is an intermediate-acting benzodiazepine that binds to the GABA-A receptor subunit to increase the frequency of chloride channel opening and facilitate membrane hyperpolarization. It is the preferred treatment for status epilepticus, although Diazepam can also be used as an alternative.

Lorazepam has a longer duration of action than Diazepam, and binds with greater affinity to the GABA-A receptor subunit.

Phenobarbital is a barbiturate that acts on the GABA-A receptor site to increase the duration of chloride channel opening. Barbiturates, particularly phenobarbital, is considered the drug of choice for seizures in infants.

Phenytoin is a sodium-channel blocker that is given for generalized tonic-clonic seizures, partial seizures, and status epilepticus. Phenytoin is preferred in prolonged therapy for status epilepticus because it is less sedating.

Propofol or thiopentone is preferred when airway protection is required.

30 mmol Na+ and 30 mmol Cl- are found in 1 litre of 0.18 percent N. saline with 4% dextrose. Percent (percent) refers to the number of grammes of a compound per 100 mL, so a litre of 4 percent dextrose solution contains 40 grammes.

As a result, a 500 mL bag of 1/5th N. saline and 4% dextrose contains approximately 15 mequivalents of sodium and 20 g of glucose. It is hypotonic due to its osmolarity of 284.

Because of the risk of hyponatraemia, it is no longer considered the crystalloid of choice for fluid maintenance in children.

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

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

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

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

When there is a fall in ionised plasma calcium levels, the chief cells of the parathyroid glands are stimulated to secrete parathyroid hormone (PTH).

50% of extracellular calcium occurs as non-ionised, protein- (albumin-)bound calcium.

The degree of ionisation increases with low ph and decreases with high pH.

There is increased renal calcium excretion with secretion of calcitonin.

Sensory innervation of the larynx is controlled by branches of the vagus nerve.

The internal and external bifurcations of the superior laryngeal nerve is responsible for sensory innervation of the aspect of the larynx superior to the vocal cords, while the recurrent laryngeal nerve is responsible for sensory innervation of the intrinsic musculature of the larynx except for the cricothyroid muscle.

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

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

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

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

The basilar artery is a large vessel that is formed by the union of the vertebral arteries at the junction of the medulla and pons. It lies in the pontine cistern and follows a shallow groove on the ventral pontine surface, extending to the upper border of the pons.

The basilar artery then bifurcates into the two posterior cerebral arteries that form part of the Circle of Willis.

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.

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).

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 liver receives blood supply from two sources.
1. Hepatic artery proper
It arises from the celiac trunk via the common hepatic artery and brings oxygenated blood to the liver.
It contributes to approximately 30% of the blood supply of the liver.
2. Hepatic portal vein – supplies the liver with partially deoxygenated blood, carrying nutrients absorbed from the small intestine. It gets tributaries from the inferior mesenteric vein, splenic vein, and superior mesenteric vein

The inferior mesenteric artery supplies the hindgut.
The superior mesenteric artery supplies the pancreas and intestine up to the proximal two-thirds of the transverse colon.
The inferior phrenic artery supplies the inferior surface of the diaphragm and oesophagus.

Charles’ Law states that there is a direct correlation between temperature and volume, where pressure and amount gas are constant. As temperature increases, volume also increases.

Boyle’s Law states that Pressure is inversely proportional to volume, assuming that temperature and amount of gas are constant. As volume increases, pressure decreases. In Dalton’s law of partial pressure, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of the gases in mixture.

According to Henry’s Law for concentration of dissolved gases, at a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. An equivalent way of stating the law is that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

Gay-Lussac’s Law states that the pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant. This law is very similar to Charles’ Law, with the only difference being the type of container. Whereas the container in a Charles’ Law experiment is flexible, it is rigid in a Gay-Lussac’s Law experiment.

The deep inguinal ring lies approximately 1.5-2cm above the midpoint of the inguinal ligament, the halfway point between the anterior superior iliac spine and the pubic tubercle, next to the epigastric vessels.

It is an important point in determining the nature of an inguinal hernia (direct or indirect). The patient is asked to cough after the hernia is reduced, with pressure applied to the deep inguinal ring. The hernia reappearing indicates it is direct, moving through the posterior wall of the inguinal canal.

Inferior and lateral to the pubic tubercle is the normal anatomical position of the neck of a femoral hernia.

Superior and medial to the pubic tubercle is the site of the superficial inguinal ring, and the normal anatomical position of the neck of an inguinal hernia.

The mid-inguinal point is located halways between the pubic symphysis and the anterior superior iliac spine. It is the surface marking for taking the femoral pulse.

Gas is composed of large numbers of molecules moving in random directions, separated by distances. They undergo perfectly elastic collisions with each other and the walls of a container and transfer kinetic energy in form of heat. These assumptions bring the characteristics of gases within the range and reasonable approximation to a real gas, particularly how any change in temperature and pressure affect the behaviour of gas. According to different theories and laws proposed, mathematical equations are derived to calculate the volume of gas, also different abbreviations are being used according to given conditions. The abbreviations used are ATP, BTPS, and STPD.
ATP stands for ambient temperature and barometric pressure, it is used to describe the conditions under which volume of gas is measured.
BTPS stands for body temperature and pressure saturated with water vapor. These are conditions under which volume of gas exist and all results of lung volume determination should be quoted at BTPS.
STPD stands for standard temperature and pressure, dry (0C and 760 mm Hg). These are the conditions that are used to describe quantities of individual gases exchanged in the lungs.

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

Mivacurium is metabolised primarily by plasma cholinesterase at an In vitro rate of about 70% that of succinylcholine. Mivacurium is contraindicated in patients with genetic and acquired plasma cholinesterase deficiencies.

The clearance of atracurium is by Hoffman degradation and ester hydrolysis in the plasma and is independent of both hepatic and renal function.

Rocuronium is eliminated primarily by the liver after metabolises to a less active metabolite, 17-desacetyl-rocuronium. Its duration of action is not affected much by renal impairment.

Vecuronium undergoes hepatic metabolism into 3-desacetyl-vecuronium which has 50-80% the activity of the parent drug. It undergoes biliary (40%) and renal excretion (30%). The aminoglycoside antibiotics possess additional neuromuscular blocking activity. The potency of gentamicin > streptomycin > amikacin. Calcium can be used to reverse the muscle weakness produced by gentamicin but not neostigmine. When vecuronium and gentamycin are given together the effect on neuromuscular blockade is synergistic.

Significant residual neuromuscular block 2 hours after the administration of these drugs is unlikely In this scenario.

Any recovery from neuromuscular blockade with suxamethonium in a patient with deficiency of plasma cholinesterase demonstrate four twitches on a train of four count.

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

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.

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

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

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

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

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

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

A tonsillar sinus or fossa is a space that is bordered by the triangular fold of the palatoglossal and palatopharyngeal arches in the lateral wall of the oral cavity. The palatine tonsils are in these sinuses.

The glossopharyngeal nerve is the main sensory nerve for the tonsillar fossa. The tonsillar branches of the glossopharyngeal nerve supply the palatine tonsils forming a plexus around it. Filaments from this plexus are distributed to the soft palate and fauces where they communicate with the palatine nerves. A lesser contribution is made by the lesser palatine nerve. Because of this otalgia may occur following tonsillectomy.

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.

Among the breathing circuits, the Lack circuit is the most efficient for spontaneous breathing.

An outer coaxial tube is present to deliver fresh air; exhaust air is routed to an inner tube, which is then delivered to a scavenging system. An expiratory valve is seen at the patient end, which is an advantage over other circuits. Moreover, the Lack circuit prevents rebreathing slightly greater than the alveolar minute ventilation at 4-5 litres per minute.

The Bain circuit prevents rebreathing at 160-200ml/kg per minute, and is a co-axial version of the Mapleson D circuit.

The Mapleson E circuit prevent rebreathing at a fresh gas flow (FGF) of approximately twice the patient’s normal minute volume. A modification of this, the Mapleson F, has a reservoir bag at the opposite end for the FGF. This circuit is appropriate for paediatric patients with a body weight less than 20 kg.

Iliacus, and Psoas major are the most important muscles that produce flexion at the hip.

They are collectively called the iliopsoas muscle. The iliacus muscle originates from the ilium while the psoas major muscle takes its origin from the lumbar vertebrae and sacrum. Their insertion is the lesser trochanter of the femur. They work together to produce flexion and external rotation of the hip. The nerve supply is from branches of the lumbar plexus (L1, 2, 3) femoral nerve (L2, 3, 4) and short direct muscular branches (T12, L1, L2, L3 and L4).

Sartorius, Rectus femoris, Tensor fasciae latae, and Pectineus muscles are two-joint muscles acting at the knee and having less influence on hip flexion:

Rectus femoris and sartorius are involved in extension of the knee. They are supplied by branches of the femoral nerve.

Myotomes associated with key movement of the lower limb are:

L1/L2 – Hip flexion
L2/L3/L4 – Hip adduction, quadriceps (knee extension)
L4/L5 – Hip abduction
L5 – Great toe dorsiflexion.

Since knee extension is not affected, L2, L3 and L4 are still intact.

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.

Sucralfate is an octasulfate of glucose to which Al(OH)3 has been added. It undergoes extensive cross-linking in an acidic environment and forms a polymer which adheres to the ulcer base for up to 6 hours and protects it from further erosion. Since it is not systemically absorbed it is virtually devoid of side effects. However, it may cause constipation in about 2% of cases due to the Aluminium component in it.

Sucralfate does not have antibacterial action against Helicobacter pylori. However, Bismuth has antibacterial action due to its oligodynamic effect.

The bispectral index (BIS) is one of several systems used in anaesthesiology as of 2003 to measure the effects of specific anaesthetic drugs on the brain and to track changes in the patient’s level of sedation or hypnosis. It is a complex mathematical algorithm that allows a computer inside an anaesthesia monitor to analyse data from a patient’s electroencephalogram (EEG) during surgery. It is a dimensionless number (0-100) that is a summative measurement of time domain, frequency domain and high order spectral parameters derived from electroencephalogram (EEG) signals.

Sleep and anaesthesia have similar behavioural characteristics but are physiologically different but BIS monitors can be used to measure sleep depth. With increasing sleep depth during slow-wave sleep, BIS levels decrease. This correlates with changes in regional cerebral blood flow when measured using positron emission tomography (PET).

BIS shows a dose-response relationship with the intravenous and volatile anaesthetic agents. Opioids produce a clinical change in the depth of sedation or analgesia but fail to produce significant changes in the BIS. Ketamine increases CMRO2 and EEG activity.

BIS is unable to predict movement in response to a surgical stimulus. Some of these are spinal reflexes and not perceived by the cerebral cortex.

BIS is used during cardiopulmonary bypass to measure depth of anaesthesia and an index of cerebral perfusion. However, it cannot predict subtle or significant cerebral damage.

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

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

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

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

CaO2 = oxygen bound to haemoglobin + oxygen dissolved in plasma

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

where:

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

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

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

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

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

The passive leg raising (PLR) manoeuvre is a method of altering left and right ventricular preload and it is done with real-time measurement of stroke volume. It is a simple, quick, relatively unbiased, and accurate bedside test to guide fluid management and avoid fluid overload.

Pulse pressure variation (PPV), Stroke volume variation (SVV), superior vena cava diameter variation (threshold 36%) and end-expiratory occlusion test are used for dynamic tests of fluid responsiveness.

PPV is derived peripherally from the arterial pressure waveform.

Stroke volume variation (SVV) can be derived peripherally through pulse contour analysis of the arterial waveform. PPV and SVV have a threshold of 12% but since they are not used in patients who have cardiac arrhythmias, are spontaneous breathing, and in ventilated patients with low lung compliance and tidal volumes, they are of limited value.

The tests of fluid responsiveness’ accuracy is determined by calculating the area under the receiver operating characteristic curve (UROC) obtained by plotting the sensitivity of the parameter in predicting fluid responsiveness vs. 1-specificity.

Under optimal conditions, the ability to determine the need for fluid is best with PPV>SVV>LVEDA>CVP.

Central venous pressure (CVP) is a static test of preload (not preload responsiveness) and a key determinant of cardiac function. The left ventricular end-diastolic area (LVEDA) a static test of fluid responsiveness, is derived using echocardiography

The external iliac artery is the larger of the two branches of the common iliac artery. It forms the main blood supply to the lower limbs. The common iliac bifurcates into the internal and external iliac artery anterior to the sacroiliac joint.

The external iliac artery courses on the medial border of the psoas major muscles and exits the pelvic girdle posterior to the inguinal ligament. Here, midway between the anterior superior iliac spine and the pubic symphysis, the external iliac artery becomes the femoral artery and descends along the anteromedial part of the thigh in the femoral triangle.

The pectineus forms the posterior border of the femoral canal.
The femoral vein forms the lateral border of the femoral canal.
The medial border of the adductor longus muscle forms the medial wall of the femoral triangle.
The medial border of the sartorius muscle forms the lateral wall of the femoral triangle.

Hydrochloric acid is lost when you vomit for a long time (HCl). As a result, the following can be expected, in varying degrees of severity:

Hypokalaemia
Hypochloraemia
Increased bicarbonate to compensate for chloride loss and metabolic alkalosis

The alkalosis causes potassium to move from the intracellular to the extracellular compartment at first. Long-term vomiting and dehydration cause potassium to be excreted by the kidneys in order to conserve sodium. Dehydration can cause urea and creatinine levels to rise.

The actual base excess is always greater than the standard base excess.

The actual base excess (BE) is a measurement of a base’s contribution to a blood gas picture’s metabolic component. It’s the amount of base that needs to be added to a blood sample to bring the pH back to 7.4 after the respiratory component of a blood gas picture has been corrected (PaCO2 of 40 mmHg or 5.3 kPa). The BE has a normal range of +2 to 2. A large positive BE indicates a severe metabolic alkalosis, while a large negative BE indicates a severe metabolic acidosis. As a result, the actual BE in vitro is unaffected by CO2.

In vivo, however, standard BE is not independent of pCO2 because blood with haemoglobin acts as a better buffer than total ECF.

As a result, it is impossible to tell the difference between compensating for a respiratory disorder and compensating for the presence of a primary metabolic disorder.

The differences between in vitro and in vivo behaviour can be mostly eliminated if the BE is calculated for a haemoglobin concentration of 50 g/L (the ‘effective’ or virtual value of Hb if it was distributed throughout the extracellular space) rather than the actual haemoglobin. Because haemoglobin has a lower buffering capacity, the standard BE is higher than the actual BE. It reflects the BE better in the extracellular space rather than just the intravascular compartment.

Standard wire gauge cannulas for intravenous and intraarterial use are available (SWG or G). The SWG is a former imperial unit (which requires metric conversion). The cross sectional area of wires is becoming more popular as a size measurement.

The number of wires that will fit into a standard hole template is referred to as SWG.

This standard sized hole can accommodate 22 thin wires side by side (each wire the diameter of a 22 gauge cannula)
In the same hole, 14 thicker wires would fit (each wire the diameter of a 14 gauge cannula)

While the diameter and thus radius of a parallel sided tube are the most important determinants of fluid flow rate, they are not commonly used to compare cannula sizes.

The circumference of French gauge (FG) catheters (urinary or chest drains) is measured. Sizes of double lumen tracheal tubes are FG. Internal diameter is used to measure single lumen tubes.

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.

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

Not publishing the results of a valid study just because they are negative or uninteresting can be termed as publication bias.

When information gathering is ill suited with respect to time i.e. collecting the data regarding a fatal disease many years after the death of its patients, it is termed as Late – look bias.

The case in point is an instance of lead time bias when upon comparing two tests, one is able to detect the condition earlier than the other but the overall outcome doesn’t change. There is a possibility that this will make the survival rates for the newer test look more promising.

The most common cause of hypoparathyroidism is injury or removing the parathyroid glands. They can be injured accidentally during surgery to remove the thyroid as they are located posterior to the thyroid gland.

A result of both low parathyroid hormone and low calcium is likely to mean that the parathyroid glands are not responding to hypocalcaemia. The hypocalcaemia can cause confusion, and the stay in the hospital is likely to refer to her surgery.

While a parathyroid adenoma is fairly common and can cause hypoparathyroidism, it much more likely causes hyperparathyroidism.

Chronic kidney disease is likely to cause hypocalcaemia, which would increase parathyroid hormone production in an attempt to increase calcium levels, causing hyperparathyroidism. Vitamin D is activated by the kidneys and then binds to calcium to be absorbed in the terminal ileum so that a deficiency would cause hyperparathyroidism.

Muscle fibre myosin ATPase histochemistry is used to divide the biochemical classification into two groups: type 1 and type II.

Type I (slow twitch) muscle fibres rely on aerobic glycolytic and aerobic oxidative metabolism to function. They have a lot of mitochondria, a good blood supply, a lot of myoglobin, and they don’t get tired easily.

Because they contain more motor units, Type II (fast twitch) muscle fibres are thicker. They are more easily fatigued, but produce powerful bursts. The capillary networks and mitochondria are less dense in these white muscle fibres than in type I fibres. They have a low myoglobin content as well.

Muscle fibres of type II (fast twitch) are divided into three types:

Type IIa – aerobic/oxidative metabolism is used.
Type IIb – anaerobic/glycolytic metabolism is used by these fibres.

When compared to skeletal muscle, cardiac and smooth muscle twitch at a slower rate.

The follicle is the functional unit of the thyroid gland. The follicular cells surround the follicle which is filled with colloid. Suspended within the colloid is the is a pro-hormone complex thyroglobulin.

The synthesis and storage of thyroid hormones is done by follicular cells and the thyroglobulin within the colloid.

Iodide ions (I−) are actively transported against a concentration gradient into the follicular cell under the influence of thyroid stimulating hormone (TSH). It then undergoes oxidation to active iodine catalysed by thyroid peroxidase (TPO). The synthesis of thyroglobulin is in the follicular cells and it contains up to 140 tyrosine residues. The tyrosine residues of thyroglobulin and active iodine are merged to form mono- and di-iodotyrosines (MIT and DIT). The iodinated thyroglobulin is then taken up into the colloid where it is stored and dimerised. Two DIT molecules are joined to produce thyroxine (T4) while one MIT and one DIT molecule are joined to produce tri-iodotyrosine (T3) by a process catalysed by TPO.

Thyroglobulin droplets are taken up as vesicles into follicular cells by pinocytosis. This process is stimulated by TSH. When these vesicles fuse with lysosomes, hydrolysis of the thyroglobulin molecules and subsequent release of T4 and T3 into the circulation occurs.

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.

The anterior cerebral artery supplies the midline portion of the frontal lobe and the superior medial parietal lobe of the brain. It also supplies the front four-fifths of the corpus callosum and provides blood to deep structures such as the anterior limb of the internal capsule, part of the caudate nucleus, and the anterior part of the globus pallidus.

The cerebral hemispheres are supplied by arteries that make up the Circle of Willis. The Circle of Willis is formed by the anastomosis of the two internal carotid arteries and two vertebral arteries.

Clinically, the internal carotid arteries and their branches are often referred to as the anterior circulation of the brain. The anterior cerebral arteries are connected by the anterior communicating artery. Near their termination, the internal carotid arteries are joined to the posterior cerebral arteries by the posterior communicating arteries, completing the cerebral arterial circle around the interpeduncular fossa, the deep depression on the inferior surface of the midbrain between the cerebral peduncles.

The middle cerebral artery supplies part of the frontal, temporal and parietal lobes.

The posterior cerebral artery supplies the occipital lobe.

Due to an increased tidal volume with little change or slight increase in respiratory rate, Minute ventilation at term is increased by about 50%. Hypothalamic function are thought to influence by Progesterone, oestradiol and prostaglandins. This causes a mild compensated respiratory alkalosis.

Maternal PaCO2 is usually decreased to about 32 mmHg (4.27 kPa) as a result of this increased alveolar ventilation at term . A compensatory decrease in serum bicarbonate from 27 to 21 mmol/L by renal excretion lessens the impact of maternal alkalosis.

Pupil size is reduced by the pupillary light reflex and during accommodation for near vision. In the pupillary light reflex, light that strikes the retina is processed by retinal circuits that excite W-type retinal ganglion cells. These cells respond to diffuse illumination. The axons of some of the W-type cells project through the optic nerve and tract to the pretectal area, where they synapse in the olivary pretectal nucleus. This nucleus contains neurons that also respond to diffuse illumination. Activity of neurons of the olivary pretectal nucleus causes pupillary constriction by means of bilateral connections with parasympathetic preganglionic neurons in the Edinger-Westphal nuclei. The reflex results in contraction of the pupillary sphincter muscles in both eyes, even when light is shone into only one eye.

The structures in the porta hepatis from anterior to posterior are:

The ducts: Most anterior are the left and right hepatic ducts.

The arteries: Next are the left and right hepatic arteries

The veins: Next is the portal vein

The epiploic foramen of Winslow lies most posterior at the porta hepatis.

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

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

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

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

Impaired ventricular relaxation reduces diastolic filling and therefore preload.

Decreased blood volume decreases preload due to reduced venous return.

Heart failure is characterized by reduced ejection fraction and therefore stroke volume.

Cardiac output = stroke volume x heart rate

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

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

Pulse pressure (is increased by stroke volume) = Systolic Pressure – Diastolic Pressure

Systemic vascular resistance = mean arterial pressure / cardiac output
Factors that increase pulse pressure include:
-a less compliant aorta (this tends to occur with advancing age)
-increased stroke volume
Aortic stenosis would decrease stroke volume as end systolic volume would increase.
This is because of an increase in afterload, an increase in resistance that the heart must pump against due to a hard stenotic valve.

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

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

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

External carotid artery originates at the upper border of the thyroid cartilage. It ascends and lies anterior to the internal carotid arteries and posterior to the posterior belly of the digastric muscle and stylohyoid muscle.

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

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.

The Tare weight of a cylinder is the weight when it is empty. So,

Weight of cylinder – tare weight = weight of remaining N2O (g).
4.44 kg – 4 kg = 0.44 kg
Here,
0.44 kg of nitrous oxide remains in the cylinder

Since the molecular weight of nitrous oxide is 44 g and one mole of an ideal gas will occupy a volume of 22.4 litres at STP
Therefore amount left in the cylinder is several (gN2O/44) x 22.4 litres of N2O.

(440/44) x 22.4 = 224 litres.

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

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

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

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

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

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

The tenth cranial nerve (vagus nerve) has both sensory and motor divisions.

It emerges from the anterolateral surface of the medulla in a groove between the olive and the inferior cerebellar peduncle as a series of 8-10 rootlets . It leaves the skull through the middle compartment of the jugular foramen and descends within the carotid sheath between the internal carotid artery and internal jugular vein. The right vagus crosses in front of the first part of the subclavian artery. It gives off the right recurrent laryngeal nerve at this point.

The left recurrent laryngeal nerve passes around the ligamentum arteriosum.

The external laryngeal nerve supplies the cricothyroid muscle while the recurrent laryngeal nerve supplies the other laryngeal muscles.

The cranial part of the accessory nerve supplies all the muscles of the palate, via the pharyngeal plexus and the pharyngeal branch of the vagus nerve, except the tensor veli palatini which is supplied by the mandibular branch of the trigeminal nerve.

The Sternothyroid, Sternohyoid, and Omohyoid muscles are supplied by the ansa cervicalis while the thyrohyoid muscle is supplied by the hypoglossal nerve.

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

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

Number needed to treat can be defined as the number of patients who need to be treated to prevent one additional bad outcome.

It can be found as:

NNT=1/Absolute Risk Reduction (rounded to the next integer since number of patients can be integer only).

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

So,

ARR= (165/1050)-(132/1044)

ARR= (0.157-0.126)

ARR= 0.031

NNT= 1/0.031

NNT=32.3

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 prostate gland is primarily supplied by the inferior vesical artery, which branches off from the anterior division of the internal iliac artery. The inferior vesical artery supplies the base of the bladder, the distal ureters, and the prostate. The branches to the prostate communicate with the corresponding vessels of the opposite side.

The inferior vesical artery branches into two main arteries:
1. Urethral artery – supplies the transition zone and is the main arterial supply for the adenomas in BPH
2. Capsular artery – supplies the glandular tissue

The venous drainage of the prostate is from the prostatic venous plexus, which drains into the paravertebral veins.

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.

Midazolam is the benzodiazepine in question. It’s the only benzodiazepine that undergoes tautomeric transformation (dynamic isomerism). The molecule is ionised and water soluble at pH 3.5, but when injected into the body at pH 7.4, it becomes unionised and lipid soluble, allowing it to easily pass through the blood brain barrier.

The half-life of midazolam is only 2-4 hours.

It is a GABAA receptor agonist because it is a benzodiazepine. GABAA receptors are found in abundance throughout the central nervous system, particularly in the cerebral cortex, hippocampus, thalamus, basal ganglia, and limbic system. GABAA receptors are ligand-gated ion channels, with the inhibitory neurotransmitter gamma-aminobutyric acid as the endogenous agonist. It is a pentameric protein (2, 2 and one subunit) that spans the cell membrane, and when the agonist interacts with the alpha subunit, a conformational change occurs, allowing chloride ions to enter the cell, resulting in neuronal hyperpolarization.

For status epilepticus, midazolam is not the drug of choice. Lorazepam is the benzodiazepine of choice for status epilepticus.