Assumptions Upon Which Rests the Validity of Pulmonary Artery Wedge Pressure Measurement

We assume certain things about the physiology of our patients, and the validity of PAWP as a measure of left atrial pressure rests on these assumptions.

Pulmonary artery wedge pressure is the same as left atrial pressure

  • Not if the catheter is outside of Wests Zone 3
  • Not if there is increased or fluctuating pulmonary artery resistance
  • How are you going to predict what that resistance is if Zone 3 is full of pus (i.e. consolidated lung is present), or if there is a huge pneumothorax there, or if there is a chest drain in the pleural cavity applying low wall suction to the system?

Left  atrial pressure is the same as left ventricular end-diastolic pressure

  • Not if the atrium is scarred and non-compliant
  • Not if the mitral valve is incompetent

Left ventricular end-diastolic pressure is a good reflection of LV end-diastolic volume

  • Not if the ventricle is scarred and non-compliant
  • Not if the mitral valve is incompetent

References

This a full-text version of the seminal paper from 1970:

The PA catheter section from The ICU Book by Paul L Marino (3rd edition, 2007) is the source for most of this information.

Additionally, Ohs Manual has a Figure 12.2 on page 111 which outlines the abovementioned assumptions, and where they are active.