An anaesthetist notices a sudden increase in peak airway pressure from 18 to 38 cmH₂O with unchanged plateau pressure during volume-controlled ventilation. The MOST likely cause is:

• A Pneumothorax — decompress immediately
• B Decreased lung compliance (pulmonary oedema, ARDS) — both peak and plateau would rise proportionally
• C Increased airway resistance (bronchospasm, kinked tube, secretions) — peak rises but plateau unchanged indicates dynamic resistance problem ✓
• D Increased tidal volume delivery by the ventilator

Explanation

Peak airway pressure reflects both resistive and elastic components. Plateau pressure (measured during an inspiratory hold) reflects only lung-chest wall compliance (elastic component). If peak rises while plateau remains unchanged, the problem is increased airway resistance (inspiratory resistance) — causes include bronchospasm, kinked/compressed ETT, endobronchial migration, large secretion plug, or biting of the tube. If both peak and plateau rise proportionally, compliance has decreased (e.g., pneumothorax, pulmonary oedema, atelectasis, abdominal distension). Driving pressure = plateau − PEEP; it predicts outcomes in ARDS.

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

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Written and medically reviewed by the StethoPrep medical team.