Pulmonary wedge pressure

The pulmonary capillary wedge pressure or PCWP (also called the pulmonary wedge pressure or PWP, or pulmonary artery occlusion pressure or PAOP) or cross-sectional pressure, is the pressure measured by wedging a pulmonary catheter with an inflated balloon into a small pulmonary arterial branch.

Physiologically, distinctions can be drawn among pulmonary artery pressure, pulmonary capillary wedge pressure, pulmonary venous pressure and left atrial pressure, but not all of these can be measured in a clinical context.

Noninvasive estimation techniques have been proposed.

Clinical significance
Because of the large compliance of the pulmonary circulation, it provides an indirect measure of the left atrial pressure.

For example, it is considered the gold standard for determining the cause of acute pulmonary edema; this is likely to be present at a PCWP of >20mmHg. It has also been used to diagnose severity of left ventricular failure and mitral stenosis, given that elevated pulmonary capillary wedge pressure strongly suggests failure of left ventricular output.

Traditionally, it was believed that pulmonary edema with normal PCWP suggested a diagnosis of acute respiratory distress syndrome (ARDS) or non cardiogenic pulmonary edema (as in opiate poisoning). However, since capillary hydrostatic pressure exceeds wedge pressure once the balloon is deflated (to promote a gradient for forward flow), a normal wedge pressure cannot  conclusively differentiate between hydrostatic pulmonary edema and ARDS.

Physiological pressure: 6–12 mm Hg.