What happens to pulmonary capillary wedge pressure (PCWP) in distributive shock?

In distributive shock, such as that seen in cases of sepsis or anaphylaxis, there is significant vasodilation and loss of vascular tone, which leads to a relative hypovolemia despite normal or increased intravascular volume. Consequently, the cardiac output may actually be maintained or increased due to increased heart rate and myocardial contractility, but the systemic vascular resistance is low.

As a result of this widespread vasodilation, the pulmonary capillary wedge pressure (PCWP) typically decreases. This decrease happens because there is an overall drop in the pressure needed to keep the pulmonary circulation filled, reflecting the low filling pressures seen in the systemic circulation due to the loss of vascular tone. Thus, in distributive shock, the pulmonary capillary wedge pressure decreases due to the inability of the blood to adequately fill the vascular system, leading to a relative decrease in blood flow resistance, impacting the pressures throughout the cardiovascular system.

In contrast to conditions like cardiogenic shock, where PCWP would increase due to heart failure and backflow of blood, or hypovolemic shock, where it may remain low but for different reasons, the decrease in PCWP during distributive shock is particularly indicative of the cardiovascular changes associated with this type of shock.