Surgical Physiology & Pharmacology Flashcards

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

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.

What is the primary mechanism by which succinylcholine (suxamethonium) produces neuromuscular blockade?

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.

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?

Answer: Pre-renal oliguria

Pre-renal oliguria is characterised by concentrated urine (osmolality >500 mOsm/kg), low urine sodium (40 mmol/L), as damaged tubules cannot concentrate urine.

Which clotting factor has the shortest half-life and is therefore the earliest indicator of synthetic liver failure?

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).

What is the Fick principle used to calculate in cardiac physiology?

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.

Which drug is used as a reversal agent for non-depolarising neuromuscular blockers and what is its mechanism?

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.