Question

Why is spinal anesthesia a cause of cardiac arrest in a patient with severe AS?

a) Due to excessive cerebrovascular vasoconstriction
b) Due to vasodilation causing reduced preload and cardiac output
c) Due to high sympathetic outflow leading to ventricular arrhythmias
d) Due to increased vagal stimulation causing severe bradycardia

Answer 1

Spinal anesthesia can cause cardiac arrest in patients with severe aortic stenosis by causing vasodilation, which reduces preload and cardiac output, critical for a heart already compromised by AS.

Step-by-step explanation:

Spinal anesthesia in a patient with severe aortic stenosis (AS) can lead to cardiac arrest primarily due to vasodilation causing a significant reduction in preload and cardiac output. This is because the administration of spinal anesthesia can result in a blockade of sympathetic nerve fibers, which normally maintain vascular tone.

This blockade leads to unopposed parasympathetic activity, causing peripheral vasodilation, which in turn decreases venous return to the heart, lowering preload and cardiac output. In patients with severe AS, the heart's ability to increase cardiac output is already compromised, and a further reduction in preload can critically lower cardiac output, increasing the risk of cardiac arrest.