Pulmonary artery catheter (PAC/Swan-Ganz catheter) wedge pressure (PAWP) of 18 mmHg in a ventilated post-cardiac-surgery patient correlates with which filling status, and at what PAWP does pulmonary oedema reliably occur?

• A Adequate filling; pulmonary oedema >30 mmHg
• B Hypovolaemia; pulmonary oedema at >40 mmHg
• C Normal filling; pulmonary oedema at >35 mmHg
• D Elevated filling pressure; pulmonary oedema occurs when PAWP exceeds plasma oncotic pressure (~18–25 mmHg) ✓

Explanation

Normal PAWP is 6–12 mmHg. PAWP 13–18 mmHg indicates moderately elevated left atrial pressure/pulmonary venous pressure; PAWP >18–20 mmHg generally correlates with onset of pulmonary congestion because it exceeds normal plasma oncotic pressure (~25 mmHg). When PAWP >25 mmHg, overt pulmonary oedema reliably occurs as hydrostatic pressure exceeds oncotic pressure, forcing fluid into alveoli. However, in hypoalbuminaemic patients, pulmonary oedema can occur at lower PAWP values. In normal hearts, PAWP approximates LVEDP, guiding fluid management in haemodynamically complex patients.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.