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HKCA Final MCQ study materials
HKCA Final MCQ study resources

HKCA Final MCQ practice questions

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Question 1Anaesthesiology

A patient with a known egg allergy requires emergency surgery. Which neuromuscular blocking agent is most strongly associated with allergic cross-reactivity in this setting?

  1. Atracurium
  2. Rocuronium
  3. Cisatracurium
  4. Suxamethonium Correct answer.

Explanation

Suxamethonium contains a quaternary ammonium group and has been linked to allergic reactions in patients with egg allergy, though the true culprit is often the shared ammonium epitope rather than egg protein itself. Rocuronium can also cause anaphylaxis but is not the classic egg-linked agent. Clinicians should still assess the nature of the reported allergy carefully before choosing any relaxant.

Question 2Anaesthesiology

Which inhalational agent has the lowest blood:gas partition coefficient and therefore the fastest equilibration with alveolar partial pressure?

  1. Sevoflurane
  2. Isoflurane
  3. Desflurane Correct answer.
  4. Enflurane

Explanation

The blood:gas partition coefficient determines how quickly an agent equilibrates between blood and alveoli; a lower coefficient means faster induction and recovery. Desflurane has the lowest value of the volatile agents in common use, followed by sevoflurane. Isoflurane and enflurane have higher coefficients and slower kinetics.

Question 3Anaesthesiology

During rapid sequence induction in a trauma patient, which action best reduces the risk of aspiration during laryngoscopy?

  1. Administering a defasciculating dose of a non-depolarising relaxant
  2. Placing the patient in a steep head-up position
  3. Applying cricoid pressure while awaiting the airway Correct answer.
  4. Pre-oxygenating with 100% oxygen for five minutes

Explanation

Cricoid pressure compresses the oesophagus against the cervical spine, aiming to occlude the upper oesophageal lumen and reduce passive regurgitation during induction. Pre-oxygenation and positioning are useful adjuncts but do not directly protect against aspiration. A defasciculating dose is not relevant to aspiration risk.

Question 4Anaesthesiology

Which monitoring modality provides the earliest reliable indication of malignant hyperthermia during general anaesthesia?

  1. Core temperature
  2. Serum potassium
  3. Urine output
  4. End-tidal carbon dioxide Correct answer.

Explanation

A rising end-tidal carbon dioxide despite adequate ventilation is often the earliest sign of malignant hyperthermia, reflecting a hypermetabolic state. Temperature rise occurs later and should not be relied upon for early detection. Potassium and urine output changes are secondary and less timely.

Question 5Anaesthesiology

A patient receiving a spinal anaesthetic develops hypotension with a sensory block to T4. Which mechanism primarily explains the hypotension?

  1. Direct myocardial depression from local anaesthetic
  2. Sympathetic blockade causing vasodilatation and reduced venous return Correct answer.
  3. Increased vagal tone causing bradyarrhythmia
  4. Reduced preload from surgical blood loss

Explanation

Spinal anaesthesia blocks sympathetic fibres, producing arterial and venous dilatation that lowers systemic vascular resistance and reduces venous return. This is the dominant cause of hypotension after neuraxial block. Direct myocardial depression and isolated vagal effects are less important primary mechanisms at this level.

Question 6Anaesthesiology

Which preoperative finding most strongly predicts difficult mask ventilation in an adult?

  1. Presence of a beard
  2. Mallampati class II
  3. Thyromental distance of 7 cm
  4. Body mass index above 35 Correct answer.

Explanation

Obesity, particularly a body mass index above 35, is one of the strongest independent predictors of difficult mask ventilation because of reduced chest wall compliance and increased soft tissue. The other listed features are either normal findings or weaker predictors. Combining predictors improves the overall assessment.

Question 7Anaesthesiology

Which agent is the first-line specific treatment for malignant hyperthermia once the crisis is recognised?

  1. Procainamide
  2. Sodium bicarbonate
  3. Dantrolene sodium Correct answer.
  4. Magnesium sulphate

Explanation

Dantrolene inhibits calcium release from the sarcoplasmic reticulum and is the specific antidote for malignant hyperthermia. Supportive measures such as stopping triggers, hyperventilation and cooling are essential but do not replace dantrolene. The other agents do not act on the underlying pathophysiology.

Question 8Anaesthesiology

A patient with severe aortic stenosis is undergoing general anaesthesia. Which haemodynamic goal is most important to maintain?

  1. Tachycardia to preserve cardiac output
  2. Reduced preload to limit pulmonary congestion
  3. Afterload reduction to improve forward flow
  4. Systemic vascular resistance and sinus rhythm Correct answer.

Explanation

In severe aortic stenosis, the hypertrophied left ventricle depends on adequate preload, afterload and a controlled heart rate to maintain coronary perfusion and cardiac output. Tachycardia shortens diastolic filling time and is poorly tolerated. Vasodilatation can cause dangerous falls in coronary perfusion pressure.

Question 9Anaesthesiology

Which statement best describes the mechanism of action of suxamethonium at the neuromuscular junction?

  1. It depolarises the motor endplate persistently, causing initial fasciculations. Correct answer.
  2. It blocks presynaptic calcium channels to reduce transmitter release.
  3. It inhibits acetylcholinesterase in the synaptic cleft.
  4. It competitively antagonises acetylcholine at the postjunctional receptor.

Explanation

Suxamethonium is a depolarising blocker that binds to the postjunctional nicotinic receptor and maintains depolarisation, producing initial fasciculations followed by flaccid paralysis. It is metabolised by plasma cholinesterase. Competitive antagonism and acetylcholinesterase inhibition describe other drug classes.

Question 10Anaesthesiology

A patient with prolonged apnoea after suxamethonium is found to have a homozygous atypical plasma cholinesterase variant. Which management step is most appropriate while awaiting recovery?

  1. Provide continued mechanical ventilation and sedation Correct answer.
  2. Give a further dose of suxamethonium
  3. Transfuse fresh frozen plasma
  4. Administer neostigmine to reverse the block

Explanation

Prolonged paralysis from atypical plasma cholinesterase is managed supportively with continued ventilation and sedation until the drug is cleared. Neostigmine does not reverse a phase I depolarising block and may worsen it. Further suxamethonium would prolong paralysis.

Question 11Anaesthesiology

Which finding on capnography most suggests oesophageal intubation rather than tracheal intubation?

  1. A stable waveform with a normal end-tidal value
  2. A gradual rise in end-tidal carbon dioxide over minutes
  3. A waveform with a sloping expiratory plateau
  4. Absent or rapidly diminishing end-tidal carbon dioxide Correct answer.

Explanation

Oesophageal intubation typically produces no sustained end-tidal carbon dioxide because no gas exchange occurs in the oesophagus. A brief low reading may appear from gas in the stomach but rapidly disappears. A stable waveform confirms tracheal placement.

Question 12Anaesthesiology

During a general anaesthetic, a patient's peak airway pressure rises and end-tidal carbon dioxide falls. Which cause should be considered first?

  1. Bronchospasm
  2. Circuit disconnection Correct answer.
  3. Pulmonary embolism
  4. Endobronchial intubation

Explanation

A sudden fall in end-tidal carbon dioxide with a rise in peak pressure can occur with a circuit disconnection, although disconnection more typically causes loss of the waveform and low pressures. The combination of high peak pressure and low end-tidal carbon dioxide should prompt systematic checks of the circuit and airway. Among the listed options, disconnection is the most immediately life-threatening and correctable cause to exclude.

Question 13Anaesthesiology

A patient requires a drug that provides amnesia and anxiolysis with minimal cardiovascular depression for awake fibreoptic intubation. Which agent best fits this role?

  1. Thiopentone
  2. Midazolam Correct answer.
  3. Ketamine
  4. Propofol

Explanation

Midazolam provides anxiolysis and anterograde amnesia with relatively modest cardiovascular effects, making it useful for sedation during awake fibreoptic intubation. Propofol and thiopentone cause more hypotension, and ketamine provides analgesia and dissociation rather than reliable amnesia.

Question 14Anaesthesiology

Which local anaesthetic property determines the maximum safe dose in an adult?

  1. The pKa of the agent
  2. The rate of systemic absorption relative to toxicity threshold Correct answer.
  3. Protein binding and lipid solubility
  4. The pH of the preparation

Explanation

Maximum safe doses are derived from the systemic toxicity threshold and the rate of absorption from the site of administration. Lipid solubility and protein binding influence potency and duration but not directly the maximum dose. pKa determines onset speed rather than the safe dose limit.

Question 15Anaesthesiology

A patient receiving bupivacaine develops perioral tingling and tinnitus. What is the most appropriate immediate action?

  1. Administer a beta-blocker
  2. Continue the block and monitor closely
  3. Stop administration and manage as local anaesthetic systemic toxicity Correct answer.
  4. Give further local anaesthetic to complete the block

Explanation

Perioral tingling and tinnitus are early features of local anaesthetic systemic toxicity, reflecting central nervous system excitation. Administration should stop immediately and the patient managed according to toxicity protocols, including airway support and lipid emulsion if severe. Continuing the block risks progression to seizures and cardiovascular collapse.

Question 16Anaesthesiology

Which agent is preferred for induction in a haemodynamically unstable patient with a full stomach requiring rapid sequence induction?

  1. Thiopentone
  2. Propofol
  3. Sevoflurane
  4. Etomidate Correct answer.

Explanation

Etomidate provides rapid induction with minimal cardiovascular depression, which is valuable in unstable patients. Propofol and thiopentone cause significant hypotension in hypovolaemic patients. Sevoflurane is not the standard choice for rapid sequence induction in this setting.

Question 17Anaesthesiology

Which nerve block is most appropriate for postoperative analgesia after open inguinal hernia repair?

  1. Ilioinguinal and iliohypogastric nerve block Correct answer.
  2. Sciatic nerve block
  3. Interscalene block
  4. Femoral nerve block

Explanation

The ilioinguinal and iliohypogastric nerves supply the inguinal region and are targeted for analgesia after inguinal hernia repair. Interscalene block affects the shoulder, femoral block affects the anterior thigh, and sciatic block affects the lower leg. Choosing the block that matches the surgical dermatome is essential.

Question 18Anaesthesiology

Which physiological change is most characteristic of a high spinal anaesthetic reaching the cervical dermatomes?

  1. Increased respiratory rate
  2. Hyperreflexia
  3. Bradycardia and hypotension Correct answer.
  4. Hypertension and tachycardia

Explanation

High neuraxial blockade interrupts cardiac sympathetic fibres, causing bradycardia and hypotension, sometimes severe. The loss of sympathetic tone reduces venous return and cardiac output. Hypertension and tachycardia are not features of high spinal anaesthesia.

Question 19Anaesthesiology

A patient with chronic obstructive pulmonary disease is undergoing general anaesthesia. Which ventilatory strategy best reduces the risk of dynamic hyperinflation?

  1. Applying high positive end-expiratory pressure
  2. Increasing tidal volume to improve oxygenation
  3. Increasing respiratory rate to lower carbon dioxide
  4. Prolonging expiratory time and accepting permissive hypercapnia Correct answer.

Explanation

Prolonging expiration allows complete exhalation and reduces air trapping in patients with obstructive disease. Accepting permissive hypercapnia avoids excessive minute ventilation. High respiratory rates, large tidal volumes and excessive positive end-expiratory pressure can all worsen dynamic hyperinflation.

Question 20Anaesthesiology

Which feature of a supraglottic airway device most limits its use during prolonged positive pressure ventilation?

  1. Requirement for muscle relaxation
  2. Inability to monitor end-tidal carbon dioxide
  3. A lower seal pressure than a tracheal tube Correct answer.
  4. Inability to provide any positive pressure ventilation

Explanation

Supraglottic airways provide a lower oropharyngeal seal pressure than a cuffed tracheal tube, so high inflation pressures risk leak and gastric insufflation. They can deliver positive pressure ventilation within limits. Capnography can be monitored through them, and muscle relaxation is not mandatory.

Question 21Anaesthesiology

A patient receiving total intravenous anaesthesia with propofol develops a sudden rise in bispectral index despite an unchanged infusion rate. Which explanation is most likely?

  1. A malfunction of the infusion pump delivering less drug
  2. Improved depth of anaesthesia
  3. Development of tolerance within minutes
  4. An increase in surgical stimulation Correct answer.

Explanation

A rising bispectral index during steady infusion most often reflects increased surgical stimulation or a lighter plane of anaesthesia. A pump malfunction delivering less drug would also raise the index but is less common than stimulation. Tolerance does not develop within minutes.

Question 22Anaesthesiology

A patient with a known phaeochromocytoma is undergoing resection. Which intraoperative event is most likely to precipitate a hypertensive crisis?

  1. Induction with propofol
  2. Application of positive end-expiratory pressure
  3. Use of a volatile agent
  4. Administration of a beta-blocker before alpha-blockade Correct answer.

Explanation

Giving a beta-blocker before adequate alpha-blockade leaves unopposed alpha-mediated vasoconstriction and can precipitate a severe hypertensive crisis. Adequate alpha-blockade must precede any beta-blockade. Propofol, volatile agents and positive end-expiratory pressure are not the classic precipitants.

Question 23Anaesthesiology

Which change in the oxyhaemoglobin dissociation curve is expected in a patient with chronic anaemia and elevated 2,3-diphosphoglycerate?

  1. A left shift reducing tissue oxygen delivery
  2. No change in the curve position
  3. A right shift enhancing tissue oxygen unloading Correct answer.
  4. A left shift caused by increased pH

Explanation

Elevated 2,3-diphosphoglycerate shifts the oxyhaemoglobin dissociation curve to the right, reducing haemoglobin oxygen affinity and enhancing unloading at the tissues. This is an adaptive response to chronic anaemia. A left shift would impair tissue oxygen delivery.

Question 24Anaesthesiology

During one-lung ventilation, which strategy best reduces the risk of hypoxaemia while limiting lung injury?

  1. Zero end-expiratory pressure throughout
  2. High inspired oxygen concentration alone
  3. Low tidal volume with adequate positive end-expiratory pressure and recruitment Correct answer.
  4. Large tidal volumes to the dependent lung

Explanation

Protective one-lung ventilation uses low tidal volumes with appropriate positive end-expiratory pressure and recruitment manoeuvres to limit ventilator-induced lung injury while improving oxygenation. Large tidal volumes increase injury risk, and zero end-expiratory pressure promotes atelectasis. High inspired oxygen alone does not address the underlying mechanics.

Question 25Anaesthesiology

A patient with severe pre-eclampsia requires general anaesthesia for caesarean delivery. Which agent is most appropriate for induction to limit the hypertensive response to laryngoscopy?

  1. Propofol
  2. Thiopentone Correct answer.
  3. Magnesium sulphate
  4. Suxamethonium

Explanation

Thiopentone has traditionally been used for induction in severe pre-eclampsia because it blunts the hypertensive response to laryngoscopy while maintaining cardiovascular stability. Suxamethonium is used for rapid sequence but does not primarily control the pressor response. Magnesium sulphate is an anticonvulsant, not an induction agent.

Question 26Anaesthesiology

Which intravenous induction agent is most associated with pain on injection into a small peripheral vein?

  1. Propofol Correct answer.
  2. Thiopentone
  3. Etomidate
  4. Ketamine

Explanation

Propofol is formulated as an emulsion and commonly causes burning or pain during peripheral injection, particularly in small veins; lidocaine pretreatment or a larger vein reduces this. The other induction agents listed are far less frequently associated with this specific problem.

Question 27Anaesthesiology

Which monitoring modality provides the earliest reliable warning of desaturation during sedation before pulse oximetry changes?

  1. Electrocardiography
  2. Capnography via nasal sampling Correct answer.
  3. Non-invasive blood pressure
  4. Tympanic temperature

Explanation

Capnography detects apnoea and hypoventilation within seconds, whereas pulse oximetry lags behind because of the oxygen reserve and the position on the dissociation curve. This makes it valuable during procedural sedation and after extubation.

Question 28Anaesthesiology

Which muscle relaxant is most suitable for rapid sequence induction when suxamethonium is contraindicated?

  1. Rocuronium 1.2 mg/kg Correct answer.
  2. Atracurium 0.5 mg/kg
  3. Neostigmine 2.5 mg/kg
  4. Vecuronium 0.1 mg/kg

Explanation

Rocuronium at 1.2 mg/kg provides intubating conditions within about 60 seconds, comparable to suxamethonium, and can be reversed with sugammadex if needed. Lower doses of other non-depolarising agents do not achieve such rapid paralysis.

Question 29Anaesthesiology

Which intravenous fluid is most appropriate for initial resuscitation of a patient with hypovolaemia from haemorrhage while awaiting blood products?

  1. Balanced crystalloid Correct answer.
  2. 20% albumin
  3. 0.18% saline with 4% dextrose
  4. 5% dextrose

Explanation

A balanced crystalloid such as Hartmann's or Plasma-Lyte provides volume expansion with a composition closer to plasma than saline and without the free water load of dextrose solutions. Large volumes of dextrose-containing fluids worsen hyponatraemia and hyperglycaemia.

Question 30Anaesthesiology

Which preoperative assessment finding most increases the risk of aspiration during induction of anaesthesia?

  1. Controlled hypertension
  2. Mild renal impairment
  3. Well-controlled asthma
  4. Symptomatic gastro-oesophageal reflux with a hiatus hernia Correct answer.

Explanation

Reflux disease with a hiatus hernia increases the likelihood of a full stomach and impaired barrier function at the lower oesophageal sphincter, raising aspiration risk. Asthma, hypertension and mild renal impairment do not directly predispose to aspiration.

Question 31Anaesthesiology

Which regional technique provides analgesia for a patient undergoing shoulder surgery?

  1. Femoral nerve block
  2. Transversus abdominis plane block
  3. Adductor canal block
  4. Interscalene brachial plexus block Correct answer.

Explanation

The interscalene block targets the C5–C6 roots and provides reliable analgesia for shoulder and proximal humerus surgery. The other blocks listed supply the lower limb or anterior abdominal wall.

Question 32Anaesthesiology

Which physiological effect is expected from a spinal anaesthetic that blocks the sympathetic fibres to the heart?

  1. Isolated hypertension
  2. Hypertension and tachycardia
  3. Bradycardia and hypotension Correct answer.
  4. Isolated tachypnoea

Explanation

Blockade of cardiac sympathetic fibres (T1–T4) reduces contractility and chronotropy, and blockade of the splanchnic and lower thoracic fibres causes vasodilatation, producing bradycardia and hypotension. This is why vasopressors and fluids are often required.

Question 33Anaesthesiology

Which agent is used to reverse residual non-depolarising neuromuscular blockade when sugammadex is unavailable?

  1. Rocuronium
  2. Suxamethonium
  3. Neostigmine with glycopyrrolate Correct answer.
  4. Propofol

Explanation

Neostigmine is an anticholinesterase that increases acetylcholine at the neuromuscular junction to reverse non-depolarising blockade; glycopyrrolate is added to prevent bradycardia and secretions. Sugammadex is an alternative but is not always available.

Question 34Anaesthesiology

A patient with a full stomach requires rapid sequence induction. Which action best reduces the risk of aspiration during induction?

  1. Ventilating with a face mask for several minutes before intubation
  2. Providing a supraglottic airway as the first device
  3. Applying cricoid pressure during induction and intubation Correct answer.
  4. Positioning the patient supine with the head elevated 45 degrees

Explanation

Cricoid pressure compresses the oesophagus against the vertebral body to reduce passive regurgitation during induction and intubation. A supraglottic airway and prolonged mask ventilation both increase the risk of gastric insufflation and aspiration.

Question 35Anaesthesiology

A patient with anaphylaxis during anaesthesia develops hypotension, bronchospasm and a rash. Which drug is the first-line treatment?

  1. Salbutamol nebuliser alone
  2. Hydrocortisone 200 mg intravenously
  3. Chlorphenamine 10 mg intravenously
  4. Adrenaline 50 micrograms intravenously in an adult Correct answer.

Explanation

Intravenous adrenaline is the first-line treatment for anaphylaxis because it reverses vasodilatation and bronchospasm; small titrated boluses of 50 micrograms in an adult are given while fluids are administered. Antihistamines and steroids are adjuncts, not initial therapy.

Question 36Anaesthesiology

A patient with severe chronic kidney disease requires a non-depolarising muscle relaxant for a long operation. Which agent is most appropriate?

  1. Pancuronium
  2. Cisatracurium Correct answer.
  3. Suxamethonium infusion
  4. Vecuronium

Explanation

Cisatracurium undergoes organ-independent Hofmann degradation, so its duration is not prolonged in renal failure. Pancuronium and vecuronium are renally cleared and accumulate, and a suxamethonium infusion risks hyperkalaemia and prolonged block.

Question 37Anaesthesiology

Which feature of a laryngeal mask airway most limits its use in a patient with a high risk of aspiration?

  1. It causes more sore throats than a tracheal tube
  2. It does not seal the oesophagus or protect the trachea Correct answer.
  3. It is difficult to insert in edentulous patients
  4. It cannot be used with positive pressure ventilation

Explanation

A supraglottic device sits above the larynx and does not isolate the trachea from gastric contents, so it offers no reliable protection against aspiration. Sore throat and insertion difficulty are lesser concerns.

Question 38Anaesthesiology

A patient with severe pre-eclampsia needs general anaesthesia for caesarean delivery. Which agent is most appropriate for induction?

  1. Thiopentone 5 mg/kg Correct answer.
  2. Etomidate 0.3 mg/kg
  3. Ketamine 2 mg/kg
  4. Propofol 3 mg/kg

Explanation

Thiopentone at 5 mg/kg is the traditional induction agent for pre-eclampsia because it provides rapid, smooth induction while blunting the hypertensive response to laryngoscopy. Ketamine can exacerbate hypertension, and propofol at high dose may cause more hypotension.

Question 39Anaesthesiology

A patient with chronic obstructive pulmonary disease requires mechanical ventilation. Which strategy best reduces the risk of dynamic hyperinflation?

  1. A high respiratory rate with a short expiratory time
  2. A high tidal volume with a short inspiratory time
  3. Zero positive end-expiratory pressure with a high rate
  4. A long expiratory time with a low respiratory rate Correct answer.

Explanation

Prolonging expiration by reducing the respiratory rate and increasing the expiratory time allows complete exhalation and limits air trapping. A high rate or short expiratory time promotes dynamic hyperinflation.

Question 40Anaesthesiology

A patient with an epidural in labour develops a sudden severe headache after an inadvertent dural puncture. Which feature best distinguishes a post-dural puncture headache?

  1. It is associated with fever and neck stiffness
  2. It is unilateral and associated with visual aura
  3. It is worse on sitting or standing and relieved by lying flat Correct answer.
  4. It is worst on waking and improves through the day

Explanation

A post-dural puncture headache is characteristically postural, worsening on standing and improving on lying flat, due to low cerebrospinal fluid pressure. Fever and neck stiffness would suggest meningitis, and a waking headache suggests raised intracranial pressure.

Question 41Anaesthesiology

A patient receiving total intravenous anaesthesia with propofol develops a sudden rise in bispectral index despite a stable infusion. Which cause should be considered first?

  1. A decrease in the patient's temperature
  2. An increase in the depth of anaesthesia
  3. A reduction in surgical stimulation
  4. A disconnection or extravasation of the infusion line Correct answer.

Explanation

A sudden rise in BIS during stable TIVA suggests that the drug is not reaching the patient, so the line should be checked for disconnection, extravasation or occlusion. Deepening anaesthesia or reduced stimulation would lower, not raise, the index.

Question 42Anaesthesiology

A patient with a history of malignant hyperthermia requires general anaesthesia. Which agent should be avoided?

  1. Propofol
  2. Remifentanil
  3. Suxamethonium Correct answer.
  4. Rocuronium

Explanation

Suxamethonium is a known trigger for malignant hyperthermia and must be avoided in susceptible patients. Propofol, rocuronium and remifentanil are considered safe in this population.

Question 43Anaesthesiology

A patient with a tracheostomy is being ventilated. Which sign most suggests a displaced tracheostomy tube?

  1. A rise in oxygen saturation
  2. A fall in peak airway pressure
  3. A stable end-tidal carbon dioxide trace
  4. Loss of the capnography waveform with increasing airway pressure Correct answer.

Explanation

Displacement of a tracheostomy tube into the soft tissues causes loss of the capnography waveform and rising airway pressure as ventilation is delivered into tissue. A stable trace and falling pressures suggest the tube remains in the airway.

Question 44Anaesthesiology

A patient with chronic anaemia and elevated 2,3-diphosphoglycerate is expected to show which change in the oxyhaemoglobin dissociation curve?

  1. A reduced P50
  2. No change in position
  3. A leftward shift
  4. A rightward shift Correct answer.

Explanation

Elevated 2,3-DPG reduces haemoglobin oxygen affinity, shifting the dissociation curve to the right and increasing P50 so that oxygen is more readily released to tissues. A leftward shift would indicate increased affinity.

Question 45Anaesthesiology

A patient with prolonged apnoea after suxamethonium is found to have a homozygous atypical plasma cholinesterase variant. Which statement best explains the prolonged block?

  1. The drug has been given by the intramuscular route
  2. The enzyme has reduced affinity for suxamethonium, slowing hydrolysis Correct answer.
  3. The patient has developed a phase II block from a single dose
  4. Suxamethonium is renally excreted and accumulates in renal failure

Explanation

Atypical plasma cholinesterase has reduced affinity for suxamethonium, so hydrolysis is markedly slowed and paralysis is prolonged. Renal excretion and phase II block do not explain a prolonged response to a single standard dose.

Question 46Anaesthesiology

A patient with a suspected difficult airway is being preoxygenated. Which technique best prolongs the safe apnoea time?

  1. Tight-fitting mask with 100% oxygen for three minutes Correct answer.
  2. Encouraging deep breaths of room air
  3. Face mask at 50% oxygen for five minutes
  4. Nasal cannula at 2 litres per minute for one minute

Explanation

Preoxygenation with a tight-fitting mask and 100% oxygen for about three minutes denitrogenates the functional residual capacity and prolongs the safe apnoea time. Lower inspired oxygen concentrations or room air provide much less reserve.

Question 47Anaesthesiology

A patient receiving a high spinal anaesthetic develops bradycardia and hypotension. Which physiological mechanism best explains the bradycardia?

  1. Reflex tachycardia from baroreceptor activation
  2. Increased venous return to the right atrium
  3. Blockade of cardiac accelerator fibres with unopposed vagal tone Correct answer.
  4. Direct vagal blockade by the local anaesthetic

Explanation

A high spinal anaesthetic blocks the cardiac sympathetic fibres (T1–T4), leaving vagal tone unopposed and causing bradycardia, alongside vasodilatation from lower thoracic and splanchnic blockade. It is not caused by direct vagal blockade or increased venous return.

Question 48Anaesthesiology

A 68-year-old man with ischaemic heart disease is undergoing elective surgery. Which inhalational agent is least likely to cause coronary steal by vasodilating coronary arteries?

  1. Halothane Correct answer.
  2. Isoflurane
  3. Sevoflurane
  4. Desflurane

Explanation

Halothane causes relatively little coronary vasodilatation and is the agent classically associated with the lowest risk of coronary steal phenomenon. Isoflurane and, to a lesser extent, desflurane and sevoflurane produce coronary vasodilatation that can divert flow away from stenosed territories.

Question 49Anaesthesiology

A 45-year-old woman receives a bolus of remifentanil during induction. Which property best explains why remifentanil has a very short context-sensitive half-time even after prolonged infusion?

  1. It undergoes hepatic glucuronidation
  2. It is metabolised by non-specific plasma esterases Correct answer.
  3. It is excreted unchanged by the kidney
  4. It has a small volume of distribution

Explanation

Remifentanil is cleared by non-specific plasma and tissue esterases, so its elimination is independent of hepatic and renal function and does not accumulate with prolonged infusion. This gives a short and constant context-sensitive half-time regardless of infusion duration.

Question 50Anaesthesiology

A patient is being ventilated with a Drager anaesthesia machine. Which adjustment to the fresh gas flow and circuit will most reduce the amount of volatile agent consumed while maintaining stable anaesthesia?

  1. Disconnecting the scavenging system
  2. Using a low-flow circle system with a soda lime absorber Correct answer.
  3. Switching to a Mapleson A circuit
  4. Increasing the fresh gas flow to 6 L/min

Explanation

A circle system with an efficient carbon dioxide absorber allows low fresh gas flows because exhaled gases are rebreathed, greatly reducing volatile agent loss. Low-flow anaesthesia also improves humidification and reduces pollution.