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Aortic Cross-Clamp Physiology — FRCA Final MCQ

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ModerateCardiothoracic AnaesthesiaAortic Cross-Clamp PhysiologyFRCA Final

A 60-year-old man (ASA III, 90 kg) is undergoing an open AAA repair. The surgeon applies the aortic cross-clamp. Which immediate physiological changes occur?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — No significant haemodynamic changes with modern anaesthetic techniques

Aortic cross-clamping causes: (1) sudden increase in afterload (increased SVR by up to 40%) above the clamp, (2) increased MAP (by 30-40%), (3) increased myocardial wall stress and oxygen demand, (4) decreased perfusion below the clamp (renal, mesenteric, spinal cord ischaemia risk), (5) redistribution of blood volume increasing preload. On unclamping: sudden decrease in SVR, hypotension (from vasodilation, washout of anaerobic metabolites, reperfusion), acidosis, and hyperkalaemia. Management requires careful titration of vasodilators (GTN, volatile agents) during clamping and vasopressors/fluid loading before unclamping.

Reference: RCOA – 2023 – Vascular anaesthesia module; NICE – 2020 – AAA management