A patient with severe COPD (FEV1 35% predicted) is posted for right hemicolectomy under general anaesthesia. Which ventilatory strategy during surgery is MOST appropriate to prevent dynamic hyperinflation?
- A High respiratory rate (20/min), low tidal volume, short expiratory time
- B High PEEP (15 cmH2O) to splint airways open
- C Low respiratory rate (8–10/min), normal tidal volume (6–8 mL/kg), prolonged expiratory time (I:E 1:3 or more) ✓
- D Normal respiratory rate with inverse I:E ratio to improve oxygenation
Correct answer: C. Low respiratory rate (8–10/min), normal tidal volume (6–8 mL/kg), prolonged expiratory time (I:E 1:3 or more)
Explanation
COPD patients have expiratory flow limitation due to loss of elastic recoil and airway collapse on expiration. A low respiratory rate with prolonged expiratory phase (I:E ≥ 1:3) allows adequate time for complete exhalation, preventing air trapping and intrinsic PEEP (auto-PEEP). High respiratory rates cause stacked breaths and dynamic hyperinflation, increasing risk of barotrauma and haemodynamic compromise. Excessively high extrinsic PEEP worsens air trapping in COPD by adding to already elevated intrinsic PEEP.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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