Pulmonary capillary wedge pressure (PCWP)
Also known as: pulmonary artery wedge pressure, wedge pressure, PAWP
Pulmonary capillary wedge pressure (PCWP) is the pressure measured by wedging a balloon-tipped catheter in a pulmonary artery branch. Normal PCWP is roughly 4–12 mmHg, and it serves as an indirect estimate of left atrial pressure.
Pulmonary capillary wedge pressure (PCWP) is obtained during right heart catheterization with a balloon-tipped (Swan-Ganz) catheter. The catheter is advanced through the right heart into a branch of the pulmonary artery, and the balloon is inflated until it wedges, blocking flow. With no flow between the catheter tip and the left heart, the pressure recorded reflects the downstream pressure — an indirect measure of left atrial pressure, and by extension left ventricular end-diastolic (filling) pressure.
A normal PCWP is roughly 4–12 mmHg. Elevated values indicate pressure backing up from the left heart: left ventricular failure, mitral stenosis, or mitral regurgitation all raise PCWP. A classic finding in mitral stenosis is a PCWP higher than the left ventricular diastolic pressure, since the stenotic valve creates a gradient between the left atrium and ventricle.
PCWP is central to distinguishing the two major forms of pulmonary edema. In cardiogenic pulmonary edema, a failing left heart drives hydrostatic pressure up, so PCWP is elevated (commonly above about 18 mmHg). In noncardiogenic edema such as ARDS, the lung capillaries leak because of inflammation while the left heart fills normally, so PCWP stays normal. The measurement also helps classify shock: elevated in cardiogenic shock, low in hypovolemic shock.
USMLE Step 1 tests PCWP in cardiovascular physiology — know the normal range, what the wedge pressure approximates, and the patterns in mitral stenosis, heart failure, ARDS, and the different shock states.
Key takeaways
- PCWP is measured with a balloon-tipped Swan-Ganz catheter wedged in a pulmonary artery branch.
- It indirectly estimates left atrial pressure and left ventricular filling pressure.
- Normal PCWP is roughly 4–12 mmHg.
- Elevated PCWP suggests left heart failure or mitral valve disease; PCWP above about 18 mmHg supports cardiogenic pulmonary edema.
- Normal PCWP with pulmonary edema points to a noncardiogenic cause such as ARDS.