Are PCWP, PAWP, and PAOP the Same?
Yes, pulmonary capillary wedge pressure (PCWP), pulmonary artery wedge pressure (PAWP), and pulmonary artery occlusion pressure (PAOP) are interchangeable terms referring to the same hemodynamic measurement. These terms all describe the pressure obtained when a balloon-tipped catheter is advanced into a pulmonary artery branch until it occludes the vessel, reflecting downstream left atrial pressure 1.
Terminology in Clinical Guidelines
The major international guidelines use these terms synonymously:
The 2015 ESC/ERS Guidelines consistently use "pulmonary artery wedge pressure (PAWP)" as the standard terminology when defining pre-capillary pulmonary hypertension (PAWP ≤15 mmHg) and post-capillary pulmonary hypertension (PAWP >15 mmHg) 1.
The 2022 ACR Appropriateness Criteria similarly employs "pulmonary arterial wedge pressure (PAWP)" when describing hemodynamic classifications of pulmonary hypertension 1.
Historical literature from 1983 refers to this measurement as "pulmonary artery occlusion pressure" while acknowledging it is commonly called "wedge pressure" 2.
What This Measurement Actually Represents
A critical caveat: Despite the name "pulmonary capillary wedge pressure," this measurement does NOT directly reflect pulmonary capillary pressure. Instead, it represents a distorted measure of pulmonary venous pressure that typically approximates left atrial pressure 3. The term "capillary" in PCWP is a historical misnomer from 1949 that persists despite being physiologically inaccurate 3.
Clinical Accuracy Considerations
When PCWP/PAWP ≤15 mmHg: This reliably indicates normal left ventricular filling pressure in pre-capillary pulmonary hypertension patients, with 90% diagnostic accuracy 4.
When PCWP/PAWP >15 mmHg: Approximately 39% of patients may actually have normal left ventricular end-diastolic pressure (LVEDP ≤15 mmHg), potentially leading to misclassification if PCWP alone is used without clinical context 4.
Correlation with left atrial pressure: When measured properly with simultaneous acquisition, PCWP demonstrates excellent correlation with directly measured left atrial pressure (correlation coefficient 0.97, mean bias 0.3 mmHg) 5.
Measurement Pitfalls
Positive end-expiratory pressure (PEEP) significantly affects the relationship between these pressures. Increasing PEEP causes PAOP/PCWP to rise relative to true capillary pressure, with minimal change in wedge pressure in open-chest conditions but marked increases in closed-chest conditions 6. This must be considered when interpreting values in mechanically ventilated patients.
Proper measurement technique is essential: The pressure should be measured at end-expiration, with the catheter properly wedged (typically 8-10 seconds after occlusion for stable readings), and analyzed in the appropriate clinical context 1, 4, 2.