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Posted by Veronica from IP on August 31, 2013 at 22:57:34:

In Reply to: Somebody help! posted by Steel on August 16, 2013 at 13:24:35:

PAWP measurement is used to obtain information about the status of the left side of the heart and the
pulmonary circulation distal to the catheter tip. There are thus two fundamental reasons for measuring
PAWP: (1) as a guide to pulmonary capillary hydrostatic pressure, and (2) as a guide to filling pressures
of the left atrium and ventricle.

PAWP is a measure of the capillary hydrostatic component that tends to force plasma fluid into the
pulmonary interstitium. This force, usually between 6 and 12 mm Hg, is opposed by the capillary
oncotic pressure (normal value, 20 to 25 mm Hg) so that fluid does not accumulate in the lungs. The
higher the PAWP or the lower the capillary oncotic pressure, the greater is the leaking tendency.

In any event, when an imbalance in oncotic and hydrostatic forces results in pulmonary edema,
measurement of PAWP can provide important therapeutic information.

When the only contributor to pulmonary edema is increased hydrostatic pressure, there is a useful
correlation between PAWP and the chest x­ray. If PAWP is less than 18 mm Hg the x­ray should not show
any signs of pulmonary edema. The minimal to moderate changes caused by pulmonary edema
(beginning with a slight vascular redistribution to the upper lobes) may be found when PAWP is between
18 to 25 mm Hg. Above 25 mm Hg, frank changes of pulmonary edema may be seen, and the higher
the PAWP is the more severe the x­ray appearance. To make these correlations it is important that the
chest x­ray be obtained close to the time that the PAWP is measured.

For example, if the chest x­ray shows definite pulmonary edema and if an accurate PAWP measurement is
10 mm Hg before the patient has received any treatment, the cause definitely is not left­sided heart
failure. Conversely, if the PAWP measurement is 35 mm Hg and the chest x­ray film is perfectly clear,
either the PAWP is in error or the chest x­ray belongs to someone else!

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