A postoperative ICU patient develops bilateral lung infiltrates, a P/F ratio of 180 mmHg, and requires FiO2 0.6 with PEEP 10 cmH2O. There is no evidence of cardiogenic oedema. Which diagnosis BEST fits, and what lung-protective ventilation tidal volume target is recommended?

• A Mild ARDS; tidal volume 10–12 mL/kg predicted body weight
• B Severe ARDS; tidal volume 4 mL/kg predicted body weight
• C Cardiogenic pulmonary oedema; tidal volume 8 mL/kg actual body weight
• D Moderate ARDS; tidal volume 6 mL/kg predicted body weight ✓

Explanation

ARDS is classified by the Berlin definition based on PaO2/FiO2 (P/F) ratio with PEEP ≥ 5 cmH2O: mild (P/F 201–300), moderate (P/F 101–200), and severe (P/F ≤ 100). This patient's P/F ratio of 180 on PEEP 10 falls in the moderate ARDS range. The ARDSNet landmark trial (ARMA) established that lung-protective ventilation with 6 mL/kg of predicted body weight reduces mortality compared with 12 mL/kg, by limiting volutrauma and barotrauma to heterogeneously damaged lungs. The absence of cardiogenic oedema and bilateral infiltrates confirm the ARDS diagnosis.

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

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Written and medically reviewed by the StethoPrep medical team.