What is the role of pulmonary artery occlusion pressure in pulmonary artery catheterization (PAC)?

Updated: Dec 22, 2017
  • Author: Bojan Paunovic, MD; Chief Editor: Karlheinz Peter, MD, PhD  more...
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Answer

Understanding the theory and required assumptions behind PCWP measurement and conditions that alter it are essential for proper use of this often misunderstood measurement. When the PAC tip is positioned properly and the balloon is inflated, the PAP tracing disappears. This occurs because inflation of the balloon causes distal migration (approximately 2 cm) of the tip into a smaller branch of the PA, where it occludes blood flow. The resulting nonpulsatile pressure tracing is called the PCWP (or pulmonary artery occlusion pressure [Ppao]) (see image below).

Pulmonary artery wedge pressure (PAWP) waveform ca Pulmonary artery wedge pressure (PAWP) waveform can be distinguished easily from the pulmonary arterial waveform in most clinical scenarios.

Under the proper circumstances, this pressure reflects the mean left atrial pressure (LAP) (see image below).

Pulmonary artery wedge pressure (PAWP) reflects le Pulmonary artery wedge pressure (PAWP) reflects left atrial pressure (LAP).

The assumption is that a static column is created between the PAC tip and the LA. This assumption is correct only if the tip is in the proper lung zone and no vascular obstruction, such as pulmonary vein stenosis, occurs downstream. When the PAC catheter balloon is inflated, the balloon stops antegrade blood flow and allows an uninterrupted column of blood to exist between the catheter tip and the LA (see images below).

Inflated balloon obstructs arterial flow and refle Inflated balloon obstructs arterial flow and reflects pressures at J point. Redrawn from Principles of Critical Care by Jesse B. Hall, Gregory A. Schmidt, Lawrence D. H. Wood, 2000, McGraw-Hill, Inc.
Having an inflated balloon in a proximal vessel is Having an inflated balloon in a proximal vessel is better because a vessel branch is likely to reflect left atrial pressure (LAP) accurately. Redrawn from Principles of Critical Care by Jesse B. Hall, Gregory A. Schmidt, Lawrence D. H. Wood, 2000, McGraw-Hill, Inc.

The PCWP waveform reflects events in the LA. The A, C, and V waves have origins similar to those that appear in the RAP waveform (see image below).

Right or left atrial pressure waveform. Right or left atrial pressure waveform.

The waveforms can be discerned by using simultaneous ECG monitoring (see image below).

Timing of the pulmonary artery waveforms in relati Timing of the pulmonary artery waveforms in relation to electrocardiographic monitoring is shown here. An A wave follows the QRS wave on ECG, whereas V wave follows the T wave on ECG.

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