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Question 1Relevant basic sciences appropriate for a specialist anaesthesiologist

A 70 kg adult has a resting oxygen consumption of 250 mL/min and an arterial oxygen content of 200 mL/L. Assuming a normal mixed venous oxygen content of 150 mL/L, what is the cardiac output?

  1. 7.5 L/min
  2. 2.5 L/min
  3. 10.0 L/min
  4. 5.0 L/min Correct answer.

Explanation

Fick principle: cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference. The difference here is 50 mL/L (0.05 L of oxygen per litre of blood), so 250/50 gives 5 L/min. This is a typical resting value and confirms the arithmetic is physiologically plausible.

Question 2Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in lung mechanics is the primary reason functional residual capacity falls in the supine position in an anaesthetised adult?

  1. Reduction in chest wall compliance from muscle relaxation
  2. Loss of surfactant activity in dependent lung regions
  3. Cephalad displacement of the diaphragm reducing thoracic volume Correct answer.
  4. Increased airway resistance from reduced bronchial calibre

Explanation

In the supine position, abdominal contents push the diaphragm cephalad, reducing the volume of the thoracic cavity at end-expiration. Anaesthesia adds further cephalad shift through loss of inspiratory muscle tone. The result is a fall in functional residual capacity and closure of small airways in dependent regions.

Question 3Relevant basic sciences appropriate for a specialist anaesthesiologist

During one-compartment pharmacokinetic modelling, which parameter describes the volume in which a drug would need to be distributed to achieve the observed plasma concentration?

  1. Clearance
  2. Elimination half-life
  3. Volume of distribution Correct answer.
  4. Bioavailability

Explanation

Volume of distribution is the apparent volume relating the amount of drug in the body to its plasma concentration. It is a proportionality constant rather than an anatomical space. Clearance describes elimination rate and half-life describes the time course of decline.

Question 4Relevant basic sciences appropriate for a specialist anaesthesiologist

A drug is a weak base with a pKa of 8.4. In plasma at pH 7.4, which statement best describes its ionisation and lipid diffusion?

  1. It is equally ionised and unionised, so diffusion is maximal
  2. It is predominantly ionised and diffuses poorly across lipid membranes Correct answer.
  3. It is predominantly ionised but still diffuses freely because of its small size
  4. It is predominantly unionised and diffuses readily across lipid membranes

Explanation

Using the Henderson-Hasselbalch relationship for a base, when pH is below pKa the protonated, ionised form predominates. A full pH unit below pKa gives roughly 90% ionisation. Charged species partition poorly into lipid bilayers, so membrane diffusion is limited.

Question 5Relevant basic sciences appropriate for a specialist anaesthesiologist

Which receptor type is responsible for the rapid depolarising effect of acetylcholine at the neuromuscular junction?

  1. Nicotinic acetylcholine receptor Correct answer.
  2. Alpha-1 adrenoceptor
  3. Muscarinic M2 receptor
  4. Muscarinic M3 receptor

Explanation

The nicotinic receptor at the motor end plate is a ligand-gated cation channel. Acetylcholine binding opens the pore, allowing sodium influx and rapid depolarisation. Muscarinic receptors are G-protein coupled and act more slowly.

Question 6Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient with chronic obstructive pulmonary disease has an arterial carbon dioxide tension of 60 mmHg and a bicarbonate of 32 mmol/L. What is the expected arterial pH?

  1. 7.33 Correct answer.
  2. 7.25
  3. 7.55
  4. 7.45

Explanation

Applying the Henderson-Hasselbalch equation with a raised carbon dioxide tension and a metabolically raised bicarbonate gives a pH only mildly reduced. The raised bicarbonate represents renal compensation for chronic hypercapnia. A value near 7.33 fits this compensated respiratory acidosis.

Question 7Relevant basic sciences appropriate for a specialist anaesthesiologist

Which of the following best describes the mechanism by which volatile anaesthetic agents produce amnesia and hypnosis at the molecular level?

  1. Competitive antagonism at nicotinic receptors at the neuromuscular junction
  2. Direct blockade of voltage-gated sodium channels in the spinal cord
  3. Inhibition of acetylcholinesterase in the central nervous system
  4. Enhancement of inhibitory GABA-A receptor currents and reduction of excitatory transmission Correct answer.

Explanation

Volatile agents potentiate GABA-A mediated chloride currents and suppress excitatory synaptic transmission. This shifts the balance toward inhibition in cortical and subcortical networks. The result is hypnosis, amnesia and immobility at increasing concentrations.

Question 8Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement correctly describes the relationship between MAC and the potency of an inhaled anaesthetic?

  1. MAC is unrelated to potency
  2. MAC equals the blood-gas partition coefficient
  3. A lower MAC indicates a more potent agent Correct answer.
  4. A higher MAC indicates a more potent agent

Explanation

MAC is the minimum alveolar concentration preventing movement in 50% of subjects to a standard stimulus. More potent agents achieve this at lower alveolar concentrations. Hence potency is inversely related to MAC.

Question 9Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient receives a depolarising neuromuscular blocker. Which sequence of events describes the normal response at the motor end plate?

  1. Competitive antagonism at the receptor with no initial contraction
  2. Blockade of acetylcholinesterase causing sustained contraction
  3. Persistent depolarisation with initial fasciculations followed by flaccid paralysis Correct answer.
  4. Presynaptic inhibition of acetylcholine release

Explanation

Depolarising blockers such as suxamethonium bind and activate the nicotinic receptor, producing transient fasciculations. Because the agent is not rapidly broken down at the end plate, the membrane remains depolarised and the receptor becomes desensitised. Flaccid paralysis follows.

Question 10Relevant basic sciences appropriate for a specialist anaesthesiologist

Which local anaesthetic property is most directly responsible for the difference in onset time between lidocaine and bupivacaine?

  1. The extent of plasma protein binding
  2. The degree of ionisation at physiological pH, reflecting pKa Correct answer.
  3. The lipid solubility of the unionised form
  4. The rate of hepatic metabolism

Explanation

Onset depends mainly on the proportion of unionised drug able to cross the nerve membrane. That proportion is determined by the pKa relative to tissue pH. Bupivacaine has a higher pKa and so a smaller unionised fraction, giving a slower onset than lidocaine.

Question 11Relevant basic sciences appropriate for a specialist anaesthesiologist

Which of the following statements about the Frank-Starling relationship in the intact heart is correct?

  1. Increasing heart rate always increases stroke volume
  2. Increasing afterload increases stroke volume at constant preload
  3. Increasing preload increases stroke volume up to a point before further increases produce no gain Correct answer.
  4. Stroke volume is independent of end-diastolic fibre length

Explanation

The Frank-Starling mechanism states that increasing end-diastolic volume increases the force of contraction. This raises stroke volume until the curve plateaus. Beyond that point, further increases in preload yield little additional output.

Question 12Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient is given a drug that blocks the sodium-potassium ATPase pump. What immediate change in the resting membrane potential would be expected?

  1. Rapid repolarisation of the action potential
  2. Gradual depolarisation as the ionic gradients run down Correct answer.
  3. Immediate hyperpolarisation from increased potassium efflux
  4. No change, because the pump is electrically neutral

Explanation

The sodium-potassium ATPase maintains the concentration gradients that set the resting potential. Blocking it allows intracellular sodium to rise and intracellular potassium to fall over time. The membrane therefore depolarises gradually as the gradients dissipate.

Question 13Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement best explains why a patient with severe aortic stenosis is at risk of myocardial ischaemia during anaesthesia?

  1. Coronary blood flow is increased but oxygen extraction is reduced
  2. The left ventricle is underfilled and cannot generate pressure
  3. Systemic vascular resistance is characteristically low, causing coronary steal
  4. Increased left ventricular wall stress raises oxygen demand while coronary perfusion is impaired Correct answer.

Explanation

In aortic stenosis the left ventricle hypertrophies and generates high systolic pressures, increasing wall stress and oxygen demand. Coronary perfusion, which occurs mainly in diastole, is compromised by the high diastolic ventricular pressure and reduced aortic diastolic pressure. The supply-demand balance is therefore precarious.

Question 14Relevant basic sciences appropriate for a specialist anaesthesiologist

Which factor most increases the risk of gastric aspiration during induction of anaesthesia?

  1. Mild systemic hypertension
  2. Delayed gastric emptying with an incompetent lower oesophageal sphincter Correct answer.
  3. Reduced functional residual capacity alone
  4. Use of a supraglottic airway in a fasted patient

Explanation

Aspiration risk depends on gastric contents reaching the airway. Delayed emptying increases gastric volume, and an incompetent lower oesophageal sphincter permits reflux into the pharynx. Together these create the conditions for aspiration during induction.

Question 15Relevant basic sciences appropriate for a specialist anaesthesiologist

A 24 kg child requires a drug at a dose of 0.1 mg/kg. The available concentration is 1 mg in 10 mL. What volume should be drawn up?

  1. 0.24 mL
  2. 2.4 mL Correct answer.
  3. 24 mL
  4. 1.2 mL

Explanation

The total dose is 0.1 mg/kg multiplied by 24 kg, giving 2.4 mg. At a concentration of 0.1 mg/mL, this requires 24 mL divided by 10, which is 2.4 mL. Checking the units confirms the result.

Question 16Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in drug handling is expected in a neonate compared with an adult?

  1. Reduced hepatic enzyme activity prolongs the elimination of many drugs Correct answer.
  2. Higher plasma albumin increases protein binding of acidic drugs
  3. Increased glomerular filtration accelerates renal clearance
  4. Increased body fat raises the volume of distribution of lipophilic drugs

Explanation

Neonatal hepatic enzyme systems are immature, so phase I and phase II metabolism is slower than in adults. Elimination of many drugs is therefore prolonged. Glomerular filtration is also reduced at birth and plasma albumin is lower.

Question 17Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about pulse oximetry is correct?

  1. It estimates arterial oxygen saturation from the ratio of light absorption at two wavelengths Correct answer.
  2. It requires a pulsatile signal, which is absent in low cardiac output states
  3. It is unaffected by carboxyhaemoglobin
  4. It measures arterial oxygen tension directly

Explanation

Pulse oximetry uses the differing absorption of red and infrared light by oxygenated and deoxygenated haemoglobin. It calculates the ratio of pulsatile to non-pulsatile absorption to estimate arterial saturation. It does not measure oxygen tension.

Question 18Relevant basic sciences appropriate for a specialist anaesthesiologist

During one-lung ventilation, which physiological change most contributes to hypoxaemia?

  1. Continued perfusion of the non-ventilated lung causing shunt Correct answer.
  2. Reduction in cardiac output reducing mixed venous oxygen content
  3. Increased ventilation of the dependent lung causing dead space
  4. Increased functional residual capacity in the ventilated lung

Explanation

When one lung is not ventilated, blood continues to pass through it without taking up oxygen. This creates a true right-to-left shunt, which is the main cause of hypoxaemia during one-lung ventilation. Hypoxic pulmonary vasoconstriction reduces but does not abolish the shunt.

Question 19Relevant basic sciences appropriate for a specialist anaesthesiologist

Which of the following best describes the physiological effect of positive end-expiratory pressure on cardiac output?

  1. It can reduce venous return and thus lower cardiac output Correct answer.
  2. It increases cardiac output by reducing afterload
  3. It always increases cardiac output by improving oxygenation
  4. It has no effect on preload

Explanation

Positive end-expiratory pressure raises intrathoracic pressure, which impedes venous return to the right heart. Reduced preload can lower stroke volume and cardiac output, particularly in hypovolaemic patients. Improved oxygenation does not necessarily offset this haemodynamic effect.

Question 20Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the pharmacokinetics of propofol is correct?

  1. It is highly protein bound and undergoes extensive hepatic and extrahepatic metabolism Correct answer.
  2. It has a very long context-sensitive half-time after prolonged infusion
  3. It is poorly lipid soluble and requires large doses
  4. It is eliminated unchanged almost entirely by the kidney

Explanation

Propofol is highly protein bound and highly lipid soluble, with rapid distribution and extensive metabolism. Clearance is high, partly through extrahepatic routes. This contributes to its relatively short context-sensitive half-time even after prolonged infusion.

Question 21Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient has a serum potassium of 6.8 mmol/L with peaked T waves on the electrocardiogram. Which treatment acts most rapidly to protect the myocardium?

  1. Intravenous calcium chloride Correct answer.
  2. Intravenous furosemide
  3. Intravenous insulin with glucose
  4. Oral sodium polystyrene sulfonate

Explanation

Calcium salts stabilise the myocardial membrane by opposing the effect of hyperkalaemia on the resting potential. This occurs within minutes and protects against arrhythmia while other measures lower the potassium. Insulin with glucose shifts potassium intracellularly but takes longer.

Question 22Relevant basic sciences appropriate for a specialist anaesthesiologist

Which mechanism explains the bradycardia and hypotension seen with a high spinal anaesthetic?

  1. Histamine release causing vasodilation
  2. Blockade of the phrenic nerve
  3. Blockade of cardiac sympathetic fibres with unopposed vagal tone and reduced venous return Correct answer.
  4. Direct myocardial depression from the local anaesthetic

Explanation

A high spinal block interrupts sympathetic outflow, causing arteriolar and venous dilation and reduced venous return. Blockade of the cardioaccelerator fibres leaves vagal tone unopposed, producing bradycardia. Together these cause hypotension.

Question 23Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about malignant hyperthermia is correct?

  1. It is inherited in an autosomal dominant pattern and is triggered by volatile agents and suxamethonium Correct answer.
  2. It is caused by a defect in acetylcholinesterase and is treated with atropine
  3. It is caused by a defect in the ryanodine receptor and is treated with beta-blockers
  4. It is inherited in an autosomal recessive pattern and is triggered by propofol

Explanation

Malignant hyperthermia is usually inherited in an autosomal dominant pattern and involves a defect in the skeletal muscle ryanodine receptor. Volatile anaesthetics and suxamethonium trigger uncontrolled calcium release. Dantrolene is the specific treatment.

Question 24Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in respiratory physiology occurs at high altitude?

  1. Hypoxic pulmonary vasoconstriction raises pulmonary artery pressure Correct answer.
  2. Alveolar oxygen tension rises while arterial carbon dioxide rises
  3. Minute ventilation falls initially
  4. The oxyhaemoglobin dissociation curve shifts to the left

Explanation

At altitude, alveolar hypoxia causes hypoxic pulmonary vasoconstriction, which raises pulmonary artery pressure. The resulting increase in ventilation also lowers arterial carbon dioxide, shifting the dissociation curve to the right. These changes are part of acclimatisation.

Question 25Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement best describes the mechanism of action of ketamine?

  1. Non-competitive antagonism at the NMDA receptor Correct answer.
  2. Agonism at opioid receptors
  3. Competitive antagonism at the GABA-A receptor
  4. Inhibition of voltage-gated calcium channels

Explanation

Ketamine acts mainly as a non-competitive antagonist at the NMDA receptor. This produces dissociative anaesthesia with analgesia and amnesia. It also has sympathomimetic effects that tend to preserve blood pressure.

Question 26Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient with chronic kidney disease has a serum potassium of 6.9 mmol/L and a sinusoid-like widened QRS. Which intravenous therapy acts fastest to stabilise the myocardium?

  1. Sodium bicarbonate 8.4%
  2. Salbutamol nebulised
  3. Insulin with glucose
  4. Calcium chloride 10% Correct answer.

Explanation

Calcium salts directly antagonise the membrane-stabilising effect of hyperkalaemia on cardiac conduction and act within minutes, so they are given first when ECG changes are present. The other measures lower serum potassium but take longer to shift the ion intracellularly.

Question 27Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the Bohr effect is correct?

  1. A fall in temperature increases oxygen unloading at the tissues
  2. A fall in 2,3-diphosphoglycerate increases tissue oxygen delivery
  3. A rise in pH reduces haemoglobin oxygen affinity
  4. A rise in carbon dioxide tension shifts the oxyhaemoglobin dissociation curve to the right Correct answer.

Explanation

Increased carbon dioxide lowers pH and increases carbamino binding, both of which reduce haemoglobin oxygen affinity so the curve shifts right and unloading improves. The other statements describe the reverse of the accepted relationships.

Question 28Relevant basic sciences appropriate for a specialist anaesthesiologist

Which nerve block is most appropriate for analgesia of the anterior two-thirds of the tongue?

  1. Greater palatine nerve block
  2. Long buccal nerve block
  3. Lingual nerve block Correct answer.
  4. Inferior alveolar nerve block

Explanation

General sensation from the anterior two-thirds of the tongue is carried by the lingual nerve, a branch of the mandibular division of the trigeminal nerve. The other listed nerves supply the teeth and lower lip, the palate, and the buccal mucosa respectively.

Question 29Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in drug response is expected in a patient with cirrhosis and hypoalbuminaemia?

  1. Prolonged effect of highly protein-bound drugs due to increased free fraction Correct answer.
  2. Reduced free fraction of highly protein-bound acidic drugs
  3. Increased volume of distribution for water-soluble drugs
  4. Enhanced first-pass metabolism of orally administered opioids

Explanation

Hypoalbuminaemia increases the unbound fraction of highly protein-bound drugs, so more active drug is available at receptor sites and the effect is prolonged. Cirrhosis also reduces intrinsic clearance, which further prolongs drug action.

Question 30Relevant basic sciences appropriate for a specialist anaesthesiologist

Which receptor type is responsible for the rapid excitatory transmission at the neuromuscular junction?

  1. Muscarinic M2 receptor
  2. Alpha-1 adrenergic receptor
  3. Gamma-aminobutyric acid type A receptor
  4. Nicotinic acetylcholine receptor Correct answer.

Explanation

Acetylcholine released from the motor nerve terminal binds to postsynaptic nicotinic receptors, which are ligand-gated cation channels that depolarise the motor end plate. This generates the end-plate potential that triggers muscle contraction.

Question 31Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the physiological dead space is correct?

  1. It is measured using the single-breath nitrogen washout test
  2. It includes alveoli that are ventilated but not perfused Correct answer.
  3. It is reduced by a decrease in tidal volume
  4. It is equal to the anatomical dead space in healthy adults

Explanation

Physiological dead space comprises the anatomical dead space plus alveolar dead space, which consists of ventilated alveoli that receive little or no perfusion. It is calculated using the Bohr equation from mixed expired and arterial carbon dioxide tensions.

Question 32Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the renal handling of sodium is correct?

  1. Aldosterone increases sodium reabsorption in the proximal tubule
  2. Sodium is actively secreted into the distal tubule
  3. Sodium reabsorption in the thick ascending limb is inhibited by thiazide diuretics
  4. Most filtered sodium is reabsorbed in the proximal convoluted tubule Correct answer.

Explanation

About two-thirds of filtered sodium is reabsorbed in the proximal convoluted tubule, largely coupled to glucose and amino acid transport and to sodium-hydrogen exchange. The remaining fraction is handled in the loop, distal tubule and collecting duct.

Question 33Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in the electrocardiogram is most characteristic of hypocalcaemia?

  1. Delta wave
  2. Prolonged QT interval Correct answer.
  3. Peaked T waves
  4. Shortened QT interval

Explanation

Low ionised calcium slows ventricular repolarisation and prolongs the QT interval, predisposing to torsades de pointes. Hypercalcaemia shortens the QT interval, while peaked T waves suggest hyperkalaemia.

Question 34Relevant basic sciences appropriate for a specialist anaesthesiologist

A 70 kg patient is receiving an infusion of a drug at 7 mg per hour. The drug has a clearance of 3.5 L per hour. What steady-state plasma concentration is expected?

  1. 0.5 mg/L
  2. 2 mg/L Correct answer.
  3. 5 mg/L
  4. 24.5 mg/L

Explanation

At steady state the concentration equals the infusion rate divided by clearance, so 7 mg/h divided by 3.5 L/h gives 2 mg/L. This relationship assumes first-order elimination and constant clearance.

Question 35Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement best explains why a patient with a large pneumothorax develops hypotension?

  1. Direct compression of the descending aorta by the pleural air
  2. Reduced right ventricular filling due to increased intrathoracic pressure and impaired venous return Correct answer.
  3. Reflex bradycardia mediated by vagal afferents from the pleura
  4. Increased systemic vascular resistance caused by hypoxia

Explanation

Raised intrapleural pressure reduces venous return to the right heart and can kink the great veins, so stroke volume and cardiac output fall. This mechanism underlies the obstructive shock of tension pneumothorax.

Question 36Relevant basic sciences appropriate for a specialist anaesthesiologist

Which property of a volatile anaesthetic is most closely related to its speed of equilibration between alveolar gas and arterial blood?

  1. Blood-gas partition coefficient Correct answer.
  2. Molecular weight of the agent
  3. Vapour pressure at 20 degrees Celsius
  4. Oil-gas partition coefficient

Explanation

A low blood-gas partition coefficient means less agent must dissolve in blood to raise its partial pressure, so alveolar and arterial partial pressures equilibrate quickly and induction is faster. The oil-gas coefficient relates to potency, not to speed of equilibration.

Question 37Relevant basic sciences appropriate for a specialist anaesthesiologist

Which mechanism best explains the analgesic effect of paracetamol?

  1. Central inhibition of prostaglandin synthesis with a possible descending serotonergic component Correct answer.
  2. Direct blockade of voltage-gated sodium channels in peripheral nerves
  3. Antagonism at mu-opioid receptors in the dorsal horn
  4. Irreversible inhibition of cyclo-oxygenase-1 in platelets

Explanation

Paracetamol acts mainly centrally, inhibiting prostaglandin synthesis and possibly engaging descending serotonergic pathways, which accounts for its antipyretic and analgesic effects with little peripheral anti-inflammatory action. It lacks clinically significant antiplatelet activity.

Question 38Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient with severe mitral stenosis becomes tachycardic during induction. Why is this poorly tolerated?

  1. Tachycardia causes reflex pulmonary vasodilation and ventilation-perfusion mismatch
  2. Tachycardia shortens diastole and further reduces left ventricular filling across the stenotic valve Correct answer.
  3. Tachycardia increases left ventricular contractility and worsens outflow obstruction
  4. Tachycardia increases the pressure gradient across the aortic valve

Explanation

In mitral stenosis, left ventricular filling depends on a prolonged diastolic filling period through a narrowed orifice, so tachycardia disproportionately reduces forward flow and raises left atrial pressure. Controlling heart rate is therefore central to anaesthetic management.

Question 39Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the measurement of arterial blood pressure using an oscillometric device is correct?

  1. The device requires a cuff width of at least half the arm circumference
  2. The mean arterial pressure is derived from the point of maximal cuff oscillation Correct answer.
  3. The diastolic pressure is measured at the point of maximal oscillation
  4. The systolic pressure is measured at the first appearance of Korotkoff sounds

Explanation

Oscillometric devices identify the cuff pressure at which oscillation amplitude is greatest, which corresponds to mean arterial pressure, and then derive systolic and diastolic values using proprietary algorithms. The first Korotkoff sound technique is auscultatory, not oscillometric.

Question 40Relevant basic sciences appropriate for a specialist anaesthesiologist

Which change in the carbon dioxide dissociation curve occurs when haemoglobin oxygen saturation falls?

  1. The curve shifts so that a given carbon dioxide content is carried at a lower partial pressure Correct answer.
  2. The curve shifts so that a given carbon dioxide content is carried at a higher partial pressure
  3. The curve is unaffected because carbon dioxide carriage is independent of haemoglobin
  4. The curve becomes identical to the oxygen dissociation curve

Explanation

Deoxygenated haemoglobin binds carbon dioxide and hydrogen ions more avidly (the Haldane effect), so at a given carbon dioxide content the partial pressure is lower. This enhances carbon dioxide uptake in the tissues and its release in the lungs.

Question 41Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the effect of positive end-expiratory pressure on the measured pulmonary capillary wedge pressure is correct?

  1. It may overestimate left ventricular end-diastolic pressure when PEEP is high Correct answer.
  2. It is unaffected by the level of applied PEEP
  3. It always reflects left atrial pressure accurately regardless of lung compliance
  4. It falls as PEEP rises because of reduced venous return

Explanation

High PEEP raises intrathoracic pressure, which is transmitted to the pulmonary vasculature and can make the wedge pressure read higher than the true left atrial pressure. Interpretation requires consideration of lung compliance and the proportion of airway pressure transmitted.

Question 42Relevant basic sciences appropriate for a specialist anaesthesiologist

Which mechanism explains the increased sensitivity of a patient with myasthenia gravis to non-depolarising neuromuscular blockers?

  1. Presynaptic failure of acetylcholine release
  2. Increased acetylcholinesterase activity at the end plate
  3. Reduced number of postsynaptic acetylcholine receptors Correct answer.
  4. Upregulation of extrajunctional acetylcholine receptors

Explanation

Myasthenia gravis is an autoimmune disease in which antibodies reduce the number of functional postsynaptic acetylcholine receptors, so a given dose of non-depolarising blocker produces a greater effect. This explains the need for reduced doses and careful monitoring.

Question 43Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the first-pass metabolism of orally administered drugs is correct?

  1. It is reduced by co-administration of grapefruit juice for all cytochrome P450 substrates
  2. It is irrelevant for drugs administered by the sublingual route
  3. It is bypassed when a drug is absorbed from the rectal mucosa above the middle rectal vein Correct answer.
  4. It increases the oral bioavailability of drugs with high hepatic extraction

Explanation

The upper rectum drains into the portal system, but the lower rectum drains partly into systemic veins, so a fraction of a rectally absorbed drug can avoid first-pass hepatic metabolism. Sublingual absorption also largely avoids first-pass metabolism.

Question 44Relevant basic sciences appropriate for a specialist anaesthesiologist

A patient with a spinal cord injury above T6 develops severe hypertension, bradycardia and sweating during bladder catheterisation. Which mechanism best explains this response?

  1. Denervation hypersensitivity of alpha receptors in the skin causes bradycardia
  2. Increased parasympathetic outflow to the gut causes hypertension
  3. Loss of descending inhibitory control allows sympathetic overactivity below the lesion with compensatory vagal bradycardia Correct answer.
  4. Direct activation of cardiac sympathetic fibres below the lesion causes tachycardia

Explanation

In autonomic dysreflexia, a noxious stimulus below the lesion triggers a massive sympathetic discharge that is unopposed because descending inhibitory pathways are interrupted, producing hypertension. Baroreceptor-mediated vagal activity then causes reflex bradycardia and flushing above the lesion.

Question 45Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the pharmacology of sugammadex is correct?

  1. It acts as an acetylcholinesterase inhibitor at the neuromuscular junction
  2. It is contraindicated in patients with renal failure because it is not excreted
  3. It is effective for reversing suxamethonium-induced block
  4. It encapsulates rocuronium and vecuronium and can reverse deep block rapidly Correct answer.

Explanation

Sugammadex is a modified gamma-cyclodextrin that encapsulates steroidal non-depolarising blockers such as rocuronium and vecuronium, reducing their free concentration and allowing rapid reversal even from deep block. The sugammadex-drug complex is excreted renally.

Question 46Relevant basic sciences appropriate for a specialist anaesthesiologist

Which mechanism best explains the reduced minimum alveolar concentration (MAC) seen in pregnancy?

  1. Increased progesterone and endogenous opioid activity in the central nervous system Correct answer.
  2. Increased plasma protein binding of volatile agents
  3. Increased cardiac output reducing alveolar anaesthetic concentration
  4. Reduced functional residual capacity increasing uptake of volatile agent

Explanation

Pregnancy reduces MAC by roughly a third, an effect attributed mainly to central modulation by progesterone and endogenous opioid peptides. Changes in cardiac output and functional residual capacity affect the speed of equilibration rather than the steady-state potency.

Question 47Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the cerebral perfusion pressure is correct?

  1. It is calculated as mean arterial pressure minus intracranial pressure Correct answer.
  2. It falls when intracranial pressure falls
  3. It is maintained constant by autoregulation across all mean arterial pressures
  4. It is calculated as systolic pressure minus central venous pressure

Explanation

Cerebral perfusion pressure equals mean arterial pressure minus intracranial pressure, assuming the brain is at the level of the reference point. Autoregulation maintains flow over a limited range of pressures but fails when the range is exceeded.

Question 48Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the interaction between volatile anaesthetics and non-depolarising neuromuscular blockers is correct?

  1. Volatile agents antagonise non-depolarising block by increasing acetylcholine release
  2. Volatile agents have no effect on the dose requirement of non-depolarising blockers
  3. Volatile agents potentiate non-depolarising block, and this effect is greater with isoflurane than with nitrous oxide Correct answer.
  4. Nitrous oxide potentiates non-depolarising block more than isoflurane does

Explanation

Volatile anaesthetics depress neuromuscular transmission and enhance the effect of non-depolarising blockers, and this potentiation is greater with agents such as isoflurane than with nitrous oxide alone. This is why neuromuscular monitoring is important when volatile agents are used.

Question 49Relevant basic sciences appropriate for a specialist anaesthesiologist

Which mechanism explains the hyperkalaemia that can follow administration of suxamethonium in a patient with burns sustained two weeks earlier?

  1. Reduced renal potassium excretion caused by the drug
  2. Direct destruction of muscle cells by the drug releases potassium
  3. Proliferation of extrajunctional acetylcholine receptors makes the whole muscle membrane sensitive to depolarisation Correct answer.
  4. Inhibition of the sodium-potassium ATPase pump by suxamethonium

Explanation

After denervation or muscle injury, extrajunctional acetylcholine receptors spread across the muscle membrane, so suxamethonium-induced depolarisation opens large numbers of channels and releases intracellular potassium. The risk peaks around one to two weeks after the injury.

Question 50Relevant basic sciences appropriate for a specialist anaesthesiologist

Which statement about the effect of hypothermia on drug metabolism and neuromuscular blockade is correct?

  1. Hypothermia slows hepatic metabolism and prolongs the action of non-depolarising blockers Correct answer.
  2. Hypothermia has no effect on the pharmacokinetics of anaesthetic drugs
  3. Hypothermia shortens the duration of vecuronium block
  4. Hypothermia increases hepatic clearance of propofol

Explanation

Core hypothermia reduces hepatic and renal blood flow and enzyme activity, slowing metabolism and elimination of many anaesthetic drugs and prolonging neuromuscular blockade. This is why temperature monitoring and active warming are routine in prolonged anaesthesia.