A patient is admitted with anaphylactic shock secondary to a blood transfusion.

Anaphylactic shock is characterized by widespread vasodilation due to the release of histamine and other inflammatory mediators. This vasodilation causes a significant drop in systemic vascular resistance and maldistribution of blood volume, leading to hypotension. The explanation addresses the pathophysiological changes that occur during anaphylactic shock. References: AACN Adult CCRN Certification Review Course, AACN CCRN Exam Handbook.