What is the target end-tidal carbon-dioxide level during hyperventilation for a patient with suspected brainstem herniation?

In cases of suspected brainstem herniation, the goal of managing ventilation involves maintaining a specific end-tidal carbon-dioxide (ETCO2) level to help regulate intracranial pressure. Hypocapnia, which occurs with hyperventilation, results in low levels of carbon dioxide in the blood, leading to vasoconstriction of cerebral blood vessels and reducing cerebral blood flow.

The target ETCO2 level during hyperventilation for such patients is typically set at 30-35 mmHg. This range usually provides an effective balance: it is low enough to induce the desired vasoconstriction to help control elevated intracranial pressure, while still keeping the physiological status of the patient stable. Keeping ETCO2 within this target helps reduce the risk of potential complications that can arise from excessively low levels of carbon dioxide, such as cerebral ischemia.

Levels below this range, such as 20-25 mmHg, would produce significant hypocapnia and could compromise cerebral blood flow too much, increasing the risk of adverse neurological outcomes. Conversely, higher ranges like 40-45 mmHg or 60-70 mmHg would not provide the desired reduction in intracranial pressure and could exacerbate the herniation process.