What is Pulmonary Capillary Wedge Pressure (PCWP)?

Pulmonary Capillary Wedge Pressure (PCWP)

Pulmonary Capillary Wedge Pressure (PCWP) is a hemodynamic measurement that serves as a surrogate for left atrial pressure and left ventricular filling pressures, obtained during right heart catheterization by wedging a balloon flotation catheter in the pulmonary vasculature. 1

Definition and Measurement

• PCWP is obtained by inflating a balloon at the tip of a pulmonary artery catheter, which occludes a small pulmonary arterial branch and creates a static column of blood between the catheter tip and the left atrium, reflecting left atrial pressure 1
• The measurement should be taken at end-expiration of a spontaneous respiratory cycle to minimize respiratory variations 1
• PCWP should be measured in multiple segments of the pulmonary vasculature to ensure accuracy, as values may vary between different lung segments 1
• End-expiratory PCWP measurements (PCWP-end Exp) provide a more reliable surrogate for left ventricular end-diastolic pressure than digitized mean PCWP (PCWP-digital), which can lead to significant underestimation 2

Clinical Significance and Interpretation

• Normal PCWP values are typically ≤12 mmHg; values >15 mmHg are considered elevated 1
• PCWP >15 mmHg excludes the diagnosis of pre-capillary pulmonary arterial hypertension (PAH) and suggests pulmonary hypertension due to left heart disease 1
• PCWP correlates best with earlier occurring left ventricular diastolic pressures such as mean PCWP, pre-A pressure, and mean LV diastolic pressure 1
• In cardiogenic shock, PCWP helps identify the phenotype (left-dominant, right-dominant, or biventricular) and guides management decisions 1

Relationship to Other Hemodynamic Parameters

• The transpulmonary gradient (mean pulmonary artery pressure minus PCWP) >12 mmHg suggests intrinsic changes in pulmonary circulation beyond passive elevation due to left heart disease 1
• Pulmonary artery diastolic pressure (PADP) can be used as a surrogate for PCWP in most cardiogenic shock phenotypes except right ventricular-predominant shock 3
• A PADP ≥24 mmHg can predict a PCWP ≥18 mmHg with ≥90% confidence in most cardiogenic shock phenotypes 3

Clinical Applications

• PCWP is essential for diagnosing and classifying pulmonary hypertension, distinguishing between pre-capillary (PAH) and post-capillary (left heart disease) etiologies 1
• It helps assess volume status and guides fluid management in critically ill patients 4
• PCWP assists in diagnosing heart failure with preserved ejection fraction (HFpEF), especially when combined with exercise hemodynamic testing 1
• In cases where PCWP measurement is technically difficult or questionable, direct measurement of left ventricular end-diastolic pressure (LVEDP) should be obtained 1

Limitations and Pitfalls

• PCWP may be inaccurate in patients with pulmonary veno-occlusive disease, where wedge pressure may be normal in some segments despite elevated left atrial pressure 1
• Misinterpretation can lead to misclassification of pulmonary hypertension, with up to 30% of patients potentially being misdiagnosed as having PAH rather than PH due to left heart disease if digital PCWP is used instead of end-expiratory measurements 2
• Patients with obesity and hypoxia are particularly at risk of misclassification if digital PCWP is used 2
• While PCWP generally correlates well with left atrial pressure, the limits of agreement may not allow complete interchangeability, especially at lower pressure ranges 5

Echocardiographic Estimation of PCWP

• Several echocardiographic parameters can estimate PCWP non-invasively, including E/e' ratio, E/A ratio, and flow propagation velocity (Vp) 1, 6
• After excluding patients with normal diastolic function using E', the conventional E/A ratio can be a reliable marker for predicting high PCWP and may be superior to E/e' in some patient populations 6
• In patients with postoperative circulatory shock and acute lung injury, an E/Ea ≥6 accurately predicts a PCWP ≥13 mmHg 4