Pharmacology in surgical practice: a free MRCS Part A question

In a shocked trauma patient the induction agent should least depress the circulation, and ketamine is the usual choice. As an NMDA receptor antagonist it produces dissociative anaesthesia while central sympathetic stimulation and reduced catecholamine reuptake tend to preserve heart rate, vascular tone and blood pressure; it also maintains airway reflexes better than other agents. Propofol and thiopental both cause dose-dependent vasodilatation and myocardial depression, so they can precipitate profound hypotension or arrest in the hypovolaemic patient unless the dose is greatly reduced. Midazolam has too slow an onset for a rapid sequence induction and also lowers blood pressure. Inhalational induction with sevoflurane is slow, leaves the full-stomach airway unprotected and vasodilates. Even ketamine is given in a reduced dose because a catecholamine-depleted myocardium may be depressed by it. Reference: BNF; Smith & Aitkenhead's Textbook of Anaesthesia 7e.