A 64-year-old hypertensive man takes ramipril 10 mg at 6 AM before reaching hospital for elective hernia repair under general anaesthesia. During maintenance he develops hypotension unresponsive to repeated fluid boluses and phenylephrine. Which property of this drug best explains the refractory vasodilatation?

• A Potentiation of succinylcholine-induced histamine release
• B Direct myocardial depression through calcium channel blockade
• C Blunting of the renin-angiotensin-aldosterone response to anaesthesia-induced vasodilatation ✓
• D Inhibition of hepatic metabolism of volatile anaesthetics

Explanation

ACE inhibitors taken on the morning of surgery are strongly associated with moderate to severe induction hypotension because they abolish the compensatory angiotensin II mediated vasoconstriction that normally offsets anaesthetic vasodilatation. The vasoplegia is often refractory to catecholamines and responds better to vasopressin or terlipressin. Conventional practice is to omit ACE inhibitors and ARBs on the morning of surgery. Ramipril causes neither myocardial depression nor interference with volatile agent metabolism.

Reference: Miller's Anesthesia, 9th ed.

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