A 30-year-old motorcyclist with polytrauma has a GCS of 8. CT chest shows bilateral pulmonary contusions. Arterial blood gas: pH 7.20, PaCO2 52 mmHg, PaO2 58 mmHg, HCO3 19 mEq/L on FiO2 1.0. He is mechanically ventilated. According to damage control resuscitation principles, the permissive hypercapnia strategy allows PaCO2 up to:

• A 45–50 mmHg
• B 60–80 mmHg ✓
• C 50–60 mmHg
• D No limit; only pH matters

Explanation

Permissive hypercapnia in lung-protective ventilation strategies for ARDS/pulmonary contusion allows PaCO2 to rise to 60–80 mmHg (some authorities up to 80–100 mmHg) to avoid high tidal volumes and plateau pressures that cause ventilator-induced lung injury. The target plateau pressure should remain ≤30 cmH2O and tidal volumes 6 mL/kg ideal body weight. The exception is severe traumatic brain injury (GCS <8 with raised ICP), where hypercapnia raises ICP through cerebral vasodilation, mandating normocarbia. In this polytrauma patient with GCS 8, ICP monitoring should guide this decision.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.