The principal mechanism of the hypotension seen after an induction dose of propofol is:
- A A marked fall in systemic vascular resistance from inhibition of sympathetic vasoconstrictor tone ✓
- B Direct release of histamine from mast cells
- C Isolated negative inotropy without any vascular effect
- D Reflex vagal discharge causing bradycardia
Correct answer: A. A marked fall in systemic vascular resistance from inhibition of sympathetic vasoconstrictor tone
Explanation
The dominant cause is a sharp drop in systemic vascular resistance produced by inhibition of sympathetic vasoconstrictor activity, compounded by impaired baroreflex compensation. Negative inotropy and reduced preload contribute but are secondary. Propofol does not cause clinically significant histamine release, which distinguishes it from agents such as atracurium, so option B is the key distractor to eliminate.
Reference: Stoelting's Pharmacology and Physiology in Anesthetic Practice, 6th ed.
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