Question

Which is the most characteristic cardiovascular effect of the inhalational anaesthetic halothane?

• A. Dose-dependent fall in cardiac output and blood pressure (often a 20-30 mm Hg drop) from myocardial depression
• B. Increase in cardiac output with reflex tachycardia
• C. Rise in systemic vascular resistance with hypertension
• D. No measurable effect on cardiac output or blood pressure

Hint:

Halothane is a myocardial depressant - expect cardiac output and BP to fall with depth.

Answer 1

The Correct Option is A

Step 1: Recall the pharmacology of halothane. Halothane is a halogenated inhalational anaesthetic that is a potent direct myocardial depressant.

Step 2: Cardiovascular effects. It produces a dose-dependent reduction in myocardial contractility and cardiac output, leading to a fall in mean arterial pressure (commonly on the order of a 20-30 mm Hg drop) that is roughly proportional to the depth of anaesthesia. Unlike many agents it does not cause a compensatory tachycardia - heart rate tends to stay the same or fall (it blunts the baroreceptor reflex).

Step 3: Arrhythmogenic potential. Halothane also sensitises the myocardium to catecholamines, predisposing to ventricular arrhythmias, especially with exogenous adrenaline or hypercarbia.

Step 4: Why the others are wrong. Halothane decreases (not increases) cardiac output, does not raise SVR/cause hypertension, and certainly is not haemodynamically neutral - its hypotensive, cardiodepressant effect is one of its defining features.

Key fact: Halothane causes a dose-dependent fall in cardiac output and blood pressure (a 20-30 mm Hg drop) through direct myocardial depression.