What is the key physiological change observed in anaphylactic shock?

The key physiological change observed in anaphylactic shock is severe vasodilation and increased vascular permeability. During anaphylaxis, the body's immune system responds to an allergen by releasing large amounts of histamine and other mediators. This results in the widening of blood vessels (vasodilation) and an increase in the permeability of vascular walls, allowing fluids to leak into surrounding tissues.

As a consequence, there is a significant drop in blood pressure due to the decreased systemic vascular resistance, and the pooling of fluid in the tissues can lead to swelling, airway obstruction, and potentially life-threatening complications. The severity of this response is what distinguishes anaphylactic shock from other types of shock, making it essential for emergency responders to quickly recognize and treat it to restore adequate perfusion and prevent organ damage.