FRCS Surgical Physiology & Pharmacology

Question 1

A patient develops hypotension, tachycardia, and cold extremities with raised CVP following cardiac surgery. What type of shock is this?

Accepted Answer

Cardiogenic shock

Answer

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?

Accepted Answer

Persistent depolarisation at the neuromuscular junction (depolarising block)

Answer

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?

Accepted Answer

Pre-renal oliguria

Answer

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?

Accepted Answer

Factor VII

Answer

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?

Accepted Answer

Cardiac output using oxygen consumption and arteriovenous oxygen difference

Answer

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.

FRCS Part A Practice Test

FRCS Part A Practice Test

FRCS Surgical Physiology & Pharmacology