The Pathophysiology of Shock in Anaphylaxis

The balance of evidence from human observations and animal studies suggests that the main pathophysiologic features of anaphylactic shock are a profound reduction in venous tone and fluid extravasation causing reduced venous return (mixed hypovolemic–distributive shock) and depressed myocardial function. Aggressive fluid resuscitation is required to ameliorate hypovolemic–distributive shock, and an intravenous infusion of epinephrine will increase vascular tone, myocardial contractility, and cardiac output in most cases. Where these measures fail, pathophysiologic considerations and anecdotal evidence support the consideration of selective vasoconstrictors as the next step in treatment.