Purpose

PAWP (Pulmonary Artery Wedge Pressure) is a left heart preload assessment measure.

As the CVP it can be changed by other factors than the volume status of the patient. , and (eg: positive pressure ventilation, cardiac compliance, mitral disease, catheter position).

Measurement

Should be measured in the distal lumen of a Pulmonary Artery Catheter (PAC), on the third West zone, after wedging with ballon insuflation. (the procedure for placement of an PAC is beyond of the scope of this article) The pressure can be measured in two ways:

• Automatically measured with the pressure monitor after wedging the catheter.
• Measured manually with the pressure tracing:
  1. Position the patient supine to a 60º angle
  2. Place and zero the transducer at a point at midaxillary line on the forth intercostal space
  3. Fill the PAC ballon with air until it’s fully inflated (usually 1,5 ml) or the pressure tracings show that the catheter it’s wedged.
  4. If the ballon it’s fully inflated but the catheter it’s not wedged advance it until it is.
  5. Measure the pressure at end diastole (at the same time that the ECG p wave), and at end expiration.

Conditions and caveats

• The measure should be done at the end of a passive expiration and the catheter tip should be at West area 3.
• It reflects the pressure at left ventricular end diastole and this should give a measure of the left heart preload. However preload it’s usually proportional to the enddiastolic volume. As the relationship between end diastolic volume and pressure (compliance) isn’t the same between patients and on the same patient in different diseases states the usefulness of this measure it’s severely limited. This is usual on left ventricular dysfunction, ischaemia, pericardial disease and when vasoactive medication it’s being used.
• Valvular heart disease (mitral and aortic) can also change the correlation between PAWP and cardiac preload
• If possible should’t be used alone to know fluid responsiveness. Better measurements are the SVV, PPV or the GEDI.

Reference Values

With the caveats above the reference values usually are: