What is the next step when measuring pulmonary artery wedge pressure (PAWP) and a wedge pressure of 28 mmHg is obtained after injecting 1 ml of air, with a pulmonary artery diastolic pressure of 14 mmHg?

Pulmonary Artery Wedge Pressure Measurement Error

Withdraw the catheter slightly before reattempting (option b) is the correct next step, as the discrepancy between the measured wedge pressure (28 mmHg) and pulmonary artery diastolic pressure (14 mmHg) indicates overwedging or catheter malposition.

Understanding the Problem

The key issue here is the large gradient between the measured "wedge" pressure (28 mmHg) and the PA diastolic pressure (14 mmHg)—a difference of 14 mmHg. 1

• In normal physiology, PAWP should approximate PA diastolic pressure, typically within 1-5 mmHg in patients without pulmonary vascular disease. 2, 3
• When PAWP significantly exceeds PA diastolic pressure, this indicates technical error in measurement, most commonly overwedging or distal catheter position. 1
• The fact that only 1 ml of air was required to obtain a "wedge" tracing is a critical red flag—proper wedge pressure measurement typically requires inflation of the balloon to its full capacity (usually 1.5 ml), and obtaining a wedge with minimal volume suggests the catheter is already too distal. 1

Why This Measurement is Incorrect

The European Society of Cardiology guidelines explicitly warn against repeated deflations and inflations of the balloon in distal pulmonary arteries because this has been associated with pulmonary artery rupture. 1

• The catheter should be inflated in the right atrium and then advanced until it reaches the PAWP position, not repeatedly inflated in distal vessels. 1
• Blood sampling with the balloon inflated in the wedge position should confirm that a true PAWP measurement has been taken, as this should have the same saturation as systemic blood. 1
• The measured value of 28 mmHg is physiologically implausible given the PA diastolic of 14 mmHg, as this would require the catheter to be measuring pressure in an occluded vessel segment rather than true left atrial pressure. 4, 2

Correct Technique for Reattempting

After withdrawing the catheter slightly, the proper technique involves: 1

• Deflate the balloon completely and withdraw the catheter to a more proximal position in the pulmonary artery.
• Re-inflate the balloon in the right atrium with the full recommended volume (typically 1.5 ml, not 1 ml).
• Advance the catheter until a wedge tracing is obtained, watching for the characteristic change from PA pressure waveform to the dampened wedge waveform.
• Verify the wedge position by confirming that the measured PAWP approximates the PA diastolic pressure (should be within a few mmHg in the absence of pulmonary vascular disease). 2, 3
• Consider blood sampling from the wedged position to confirm arterial-level oxygen saturation, validating true wedge position. 1

Why Other Options Are Incorrect

Option a (Record the value) is dangerous because this falsely elevated wedge pressure could lead to misdiagnosis and inappropriate treatment decisions, such as incorrectly classifying the patient as having post-capillary pulmonary hypertension or heart failure with elevated filling pressures. 4

Option c (Inflate to 1.5 ml) would worsen the overwedging problem and significantly increase the risk of pulmonary artery rupture, as the catheter is already too distal. 1

Option d (Leave balloon inflated) is contraindicated because prolonged balloon inflation can cause pulmonary infarction and is explicitly warned against in guidelines—the balloon should only be inflated for the brief time needed to obtain measurements. 1

Clinical Context and Pitfalls

Research has shown that PAWP measurements can have significant errors, with one study finding only modest correlation (r² = 0.75) between reported wedge pressure and PA diastolic pressure, with deviations up to 40 mmHg in some cases. 2

• Most discrepancies occur at lower and higher pressure measurements, emphasizing the importance of technical precision. 2
• When PAWP ≤15 mmHg, it reliably indicates normal left ventricular filling pressure with 90% accuracy, but elevated PAWP measurements require careful validation. 4
• In pulmonary embolism, the PA diastolic-occlusion pressure gradient can be increased (≥8 mmHg), but this represents true pathophysiology rather than measurement error and would not produce a gradient of 14 mmHg. 3