Pulmonary artery catheter: indications, waveforms, complications
Why examiners ask this
The PA catheter lets the examiner test whether I can justify an invasive monitor that has never improved mortality in trials, interpret what it tells me, and recognize when the number lies. It stresses application of knowledge (waveforms, the wedge as a surrogate for left ventricular filling) and judgment (risk against benefit, and when echo is the better tool).
The 60-second answer
I place a PA catheter when continuous right-sided pressures, cardiac output and mixed venous saturation will change what I do and echo cannot give me that continuously: severe pulmonary hypertension or right ventricular failure, liver transplantation, some cardiac surgery, and a patient with a poor ventricle facing large fluid shifts. I float it from the right internal jugular with the balloon inflated, watching the waveforms change from right atrium to right ventricle to pulmonary artery to wedge at predictable depths, and I wedge only briefly with the minimum volume. I use the wedge pressure as an estimate of left atrial pressure, knowing where it misleads, and I trend cardiac output and SvO2 rather than worship single numbers. I watch for arrhythmias during passage, the commonest complication, and for pulmonary artery rupture, which presents as hemoptysis.1
Decision points and the "why"
- Indication — routine use has not reduced morbidity or mortality,1 and the PAC-Man and ESCAPE trials showed no outcome benefit in unselected patients, so I place one only when a specific question will be answered continuously; TEE gives better structural information but needs an operator and is not a 48-hour ICU monitor.
- Right internal jugular — the straightest path to the right ventricle, with the left subclavian as the usual alternative because its gentle curve follows the catheter's course;1,2 I expect RA at 20–25 cm, RV at 30–35 cm, PA at 40–45 cm and wedge at 45–55 cm. No RV trace by 40 cm means it is coiling, so I deflate and withdraw.
- Pre-existing left bundle branch block — passage can cause right bundle branch block and therefore complete heart block,3 so I have transcutaneous pacing ready or use a pacing-capable catheter.
- Wedge overestimates LVEDP — mitral stenosis, pulmonary venous obstruction, PEEP above about 10 cmH2O and tip position in West zone 1 or 2;1 I confirm the tip is below the left atrium and read at end-expiration.
- Wedge underestimates LVEDP — a stiff ventricle and acute aortic regurgitation, where the mitral valve closes early; a normal wedge does not exclude high left ventricular pressure.
- Large v-waves — acute mitral regurgitation, ischemic papillary dysfunction or a noncompliant atrium; I treat the lesion, not the wedge number.
- Thermodilution limits — tricuspid regurgitation and intracardiac shunts make output values unreliable; I cross-check with echo and SvO2. PA diastolic pressure is a usable surrogate for the wedge unless pulmonary vascular resistance is high.1
The complication they will inject
On weaning from bypass the surgeon sees blood welling in the endotracheal tube after I wedged the catheter. This is pulmonary artery rupture until proven otherwise: rare, at about 0.03–0.2% of insertions, but often fatal, and it typically happens at the moment of wedging.1 I tell the surgeon and perfusionist immediately, deflate the balloon and pull the catheter back a few centimeters, increase PEEP, and position the bleeding side down if the chest is closed. I isolate the lung with a bronchial blocker or a double-lumen tube to protect the other side, reverse heparin with protamine if we are off bypass, and correct coagulopathy. Ongoing bleeding needs angiographic embolization or surgical repair. I reassess oxygenation and document; prevention is wedging only briefly, avoiding over-wedging, and keeping the tip proximal in anticoagulated, hypothermic or elderly patients with pulmonary hypertension.
Pitfalls that cost points
- Defending the PA catheter as an outcome-improving device.
- Reading the wedge without stating the conditions that make it wrong.
- Leaving the balloon inflated or wedging repeatedly with full volume.
- Ignoring the LBBB in the stem before floating the catheter.
- Treating a low cardiac output number without looking at the patient, the SvO2 and the echo.
Rapid-why
Q: What does a low SvO2 tell you? A: Normal is 65–75%;1 below that, oxygen delivery is not meeting demand: low output, anemia, hypoxemia or high consumption; I work through each rather than assume the heart.
Q: Why does the RV trace have a flat or rising diastolic pressure and the PA trace a falling one with a dicrotic notch? A: The RV fills in diastole, so its pressure rises; the PA is behind a closed pulmonic valve, so its pressure decays and the notch marks valve closure.
Q: Why read at end-expiration? A: Pleural pressure is closest to atmospheric then, so the transmural pressure is most accurate in both spontaneous and controlled ventilation.
Q: What is the pulmonary vascular resistance formula? A: 80 × (mean PA pressure − wedge) / cardiac output; normal is below about 2 Wood units, roughly 160 dyn·s·cm−5.
Numbers to know
| Item | Value |
|---|---|
| RA (CVP) | 0–8 mmHg1 |
| RV | 15–30 / 0–8 mmHg1 |
| PA | 15–30 / 4–14 mmHg, mean 9–161 |
| Wedge | 2–12 mmHg1 |
| SvO2 | 65–75%1 |
| PA rupture | 0.03–0.2% of insertions1 |
| Depth from right IJ | RA 20–25, RV 30–35, PA 40–45, wedge 45–55 cm |
Links
- Central venous access and its complications, Pulmonary hypertension and right ventricular failure (coming), Heart failure and reduced ejection fraction (coming), Mitral regurgitation and mitral stenosis (coming), Cardiopulmonary bypass: conduct and separation (coming)
- Atlas: Monitor atlas: perioperative cardiac events
- ASA Practice Guidelines for Pulmonary Artery Catheterization
Sources
- 1.Monitoring and Testing the Critical Care Patient (Pulmonary Artery Catheter Monitoring) · Merck Manual Professional Edition, 2026 · merckmanuals.comNormal pressures table (adapted from Fowler), PAOP limitations, complication rates; cites the ASA PAC practice guideline, which was not itself fetched.
- 2.How To Do Infraclavicular Subclavian Vein Cannulation · Merck Manual Professional Edition, 2026 · merckmanuals.com
- 3.How To Do Internal Jugular Vein Cannulation, Ultrasound-Guided · Merck Manual Professional Edition, 2026 · merckmanuals.com
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.