Pulmonary Artery Wedge Pressure
OVERVIEW
Pulmonary Artery Wedge Pressure (PAWP) is also known as Pulmonary Artery Occlusion Pressure (PAOP)
PULMONARY ARTERY WEDGE PRESSURE
- PAOP or PAWP is pressure within the pulmonary arterial system when catheter tip ‘wedged’ in the tapering branch of one of the pulmonary arteries
- in most patients this estimates LVEDP thus is an indicator of LVEDV (preload of the left ventricle)
- normally 6-12mmHg (1-5mmHg less than the pulmonary artery diastolic pressure)
- PCWP >18 mmHg in the context of normal oncotic pressure suggests left heart failure
WEDGING
“Wedging” is measurement of PAOP (pulmonary artery occlusion measurement)
- PA catheter tip advanced into a small pulmonary artery (usually in RML or RLL)
- PAWP measured by convention at end-expiration at end-diastole (ECG p wave)
- phasic blood flow and pressure ceases
- static column of blood between catheter tip in pulmonary artery and the left atrium
- must be in West Zone III otherwise trace will show respiratory swing (reflects alveolar pressure in West Zones I and II)
CHECKING THAT THE PAC TIP IS IN WEST ZONE III
5 indicators that PAC tip is in West Zone III:
- PAWP < PADP by 1-5 mmHg
- PAWP alters < than 50% of increase in PEEP
- PAWP increases by < 50% of changes in alveolar pressure (Pplat)
- O2 saturation in wedged position greater than unwedged position (sucking back of oxygenated blood)
- CXR: below level of LA
SITUATIONS WHEN PAWP IS NOT EQUIVALENT TO LVEDP
Situations when PAWP > LVEDP
- mitral stenosis
- atrial myxoma
- pulmonary venous obstruction (e.g. fibrosis, vasculitis)
- MR
- non-zone III placement
- L to R shunt
- COPD
- IPPV +/- PEEP
Situations when PAWP < LVEDP
- left ventricular failure
- raised intra-thoracic pressure (high PEEP)
- non-compliant left ventricle (e.g. hypertensive cardiomyopathy)
- aortic regurgitation
References and Links
LITFL
- CCC – Pulmonary Artery Catheters
- CCC – Pulmonary Artery Wedge Pressure and Wedging
- CCC – Troubleshooting PAC insertion
- CCC – Troubleshooting PAC measurement
- CCC – Pulmonary haemorrhage after PAOP measurement
- CCC – Pulmonary Artery Catheter Literature Summaries
- CCC – History of the Pulmonary Artery Catheter
- DerangedPhysiology.com — Pulmonary Artery Catheter (highly recommended)
- DerangedPhysiology.com — Troubleshooting the insertion of the Pulmonary Artery Catheter
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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