Head injury patients should be ventilated to achieve an arterial CO2 range of?

• A. 30-35 mmHg
• B. 25-30 mmHg
• C. 40-45 mmHg
• D. 35-40 mmHg

Answer: (D)

Maintaining normal arterial CO2 is crucial for brain blood flow after head injury. CO2 levels directly influence cerebral vessel tone: higher CO2 causes vessels to dilate and increases intracranial pressure, while very low CO2 causes constriction and can dangerously reduce blood flow to the brain. Therefore, the safest and most effective target is a normal range so that cerebral perfusion stays adequate without pushing ICP up or risking ischemia. The normal range to aim for is 35–40 mmHg.

In emergency situations with signs of impending herniation, brief, supervised hyperventilation might be used to lower PaCO2 to around 30–35 mmHg for a short period, but prolonged lowering beyond the normal range is avoided to prevent cerebral ischemia.