A 55-year-old patient with severe COPD (FEV1 28% predicted) needs anaesthesia for a femoral hernia repair. Which ventilatory strategy BEST prevents dynamic hyperinflation?
- A High tidal volume (12 mL/kg) with high respiratory rate to maintain PaCO2 at 40 mmHg
- B PEEP 10 cmH2O to open collapsed alveoli and improve oxygenation
- C Low respiratory rate (8–10/min) with prolonged expiratory time (I:E 1:3 to 1:4) and permissive hypercapnia ✓
- D Inverse ratio ventilation to maximise inspiratory time and prevent CO2 retention
Correct answer: C. Low respiratory rate (8–10/min) with prolonged expiratory time (I:E 1:3 to 1:4) and permissive hypercapnia
Explanation
Dynamic hyperinflation (breath stacking, auto-PEEP) in COPD arises from inadequate expiratory time due to high airway resistance and flow limitation. Low respiratory rate with I:E ratio ≥1:3 allows adequate expiration. Permissive hypercapnia (PaCO2 up to 55–60 mmHg) is acceptable in COPD with chronic CO2 retention. High tidal volumes worsen hyperinflation; external PEEP above intrinsic auto-PEEP increases gas trapping; inverse ratio ventilation is contraindicated in obstructive lung disease.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.