FRCS Surgical Physiology & Pharmacology — Questions and Answers
Question 1: A patient develops hypotension, tachycardia, and cold extremities with raised CVP following cardiac surgery. What type of shock is this?
- Hypovolaemic shock
- Cardiogenic shock (Correct answer)
- Distributive (septic) shock
- Obstructive shock
Correct answer: Cardiogenic shock
Cardiogenic shock is characterised by hypotension and peripheral vasoconstriction (cold, clammy extremities, tachycardia) with elevated central venous pressure (due to backward heart failure). It results from pump failure — the low CO triggers a compensatory sympathetic response causing vasoconstriction.
Question 2: What is the primary mechanism by which succinylcholine (suxamethonium) produces neuromuscular blockade?
- Competitive antagonism at nicotinic acetylcholine receptors
- Persistent depolarisation at the neuromuscular junction (depolarising block) (Correct answer)
- Inhibition of acetylcholine synthesis
- Pre-synaptic inhibition of acetylcholine release
Correct answer: Persistent depolarisation at the neuromuscular junction (depolarising block)
Suxamethonium is a depolarising neuromuscular blocking agent. It binds to nicotinic AChR at the NMJ, causing persistent depolarisation (fasciculations, then sustained blockade). Unlike non-depolarising agents, it cannot be reversed with neostigmine. Pseudocholinesterase metabolises it.
Question 3: A surgical patient develops oliguria post-operatively. Urine osmolality is 550 mOsm/kg and urine sodium is 12 mmol/L. What is the most likely cause?
- Acute tubular necrosis
- Pre-renal oliguria (Correct answer)
- Urinary retention
- Inappropriate ADH secretion
Correct answer: Pre-renal oliguria
Pre-renal oliguria is characterised by concentrated urine (osmolality >500 mOsm/kg), low urine sodium (<20 mmol/L), and a fractional excretion of sodium <1%, indicating intact tubular function conserving sodium. ATN shows dilute urine, high urine Na (>40 mmol/L), as damaged tubules cannot concentrate urine.
Question 4: Which clotting factor has the shortest half-life and is therefore the earliest indicator of synthetic liver failure?
- Factor X
- Factor VIII
- Factor V
- Factor VII (Correct answer)
Correct answer: Factor VII
Factor VII has the shortest half-life of approximately 4–6 hours and is dependent on vitamin K and hepatic synthesis. The PT/INR, which is sensitive to Factor VII, is the most sensitive early indicator of hepatic synthetic failure and is incorporated into prognostic scoring (Child-Pugh, MELD, King's College Criteria).
Question 5: What is the Fick principle used to calculate in cardiac physiology?
- Systemic vascular resistance
- Cardiac output using oxygen consumption and arteriovenous oxygen difference (Correct answer)
- Left ventricular end-diastolic pressure
- Coronary perfusion pressure
Correct answer: Cardiac output using oxygen consumption and arteriovenous oxygen difference
The Fick principle states that cardiac output = oxygen consumption / (arterial O2 content − venous O2 content). It is the gold standard for measuring cardiac output, often used during cardiac catheterisation when thermodilution is not feasible.
Question 6: Which drug is used as a reversal agent for non-depolarising neuromuscular blockers and what is its mechanism?
- Flumazenil — GABA receptor antagonist
- Sugammadex — encapsulates rocuronium/vecuronium, rendering them inactive (Correct answer)
- Naloxone — opioid receptor antagonist
- Protamine — binds and neutralises heparin
Correct answer: Sugammadex — encapsulates rocuronium/vecuronium, rendering them inactive
Sugammadex is a modified gamma-cyclodextrin that encapsulates steroidal non-depolarising neuromuscular blocking agents (rocuronium, vecuronium) within its hydrophobic core, immediately reversing blockade without muscarinic side effects. It is the preferred reversal agent over neostigmine.
FRCS Surgical Physiology & Pharmacology
A patient develops hypotension, tachycardia, and cold extremities with raised CVP following cardiac surgery.
What type of shock is this?