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Cerebral blood flow is dependent on the PaCO2 as carbon dioxide dilates the cerebral vessels. This increase is accompanied by an increase in cerebral blood volume and therefore a rise in intracranial pressure. Reduction of PaCO2 levels by increasing minute ventilation allows some control of intracranial pressure. |
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However hyperventilation will lead to hypocapnia (below PaCO2 of 4kPa - 30mmHg), and with it cerebral vasoconstriction. This can lead to hypoxia and cerebral ischaemia and should be avoided.
The primary goal of the management of traumatic brain injury is prevention of secondary neuronal damage by maintaining oxygenation and perfusion.