In isovolumic normal human subjects, 1 MAC of isoflurane anesthesia depresses mean arterial pressure by approximately 25%. The single BEST explanation for this is

In isovolumic normal human subjects, 1 MAC of isoflurane anesthesia depresses mean arterial pressure by approximately 25%. The single BEST explanation for this is

• A. Reduction in heart rate
• B. Venous pooling
• C. Myocardial depression
• D. Decreased systemic vascular resistance

Answer: (D)

Volatile anesthetics like isoflurane mainly cause systemic vasodilation, which lowers afterload. Mean arterial pressure reflects both cardiac output and systemic vascular resistance (MAP ≈ CO × SVR). At 1 MAC, isoflurane reduces SVR by relaxing vascular smooth muscle and blunting sympathetic tone, so arterial pressure falls even if cardiac output remains relatively stable. While changes in heart rate or preload can influence MAP, the predominant effect at this dose is decreased systemic vascular resistance, making it the best explanation for the ~25% drop in MAP. Venous pooling or modest myocardial depression may contribute slightly, but they don’t account as well for the magnitude of the change as the marked vasodilation does.

Volatile anesthetics like isoflurane mainly cause systemic vasodilation, which lowers afterload. Mean arterial pressure reflects both cardiac output and systemic vascular resistance (MAP ≈ CO × SVR). At 1 MAC, isoflurane reduces SVR by relaxing vascular smooth muscle and blunting sympathetic tone, so arterial pressure falls even if cardiac output remains relatively stable. While changes in heart rate or preload can influence MAP, the predominant effect at this dose is decreased systemic vascular resistance, making it the best explanation for the ~25% drop in MAP. Venous pooling or modest myocardial depression may contribute slightly, but they don’t account as well for the magnitude of the change as the marked vasodilation does.