Thus as arterial pressure rises so CBF will rise causing an increase in cerebral volume. More recent work has shown that following trauma autoregulation may still be functioning. In this situation if CPP falls below the critical value of 70 mmHg, the patient will have inadequate cerebral perfusion. Autoregulation will cause cerebral vasodilatation leading to a rise in brain volume. This explains why the maintenance of arterial blood pressure at adequate level by careful monitoring and rapid correction if it falls is so important.
Carbon dioxide causes cerebral vasodilation.
Therefore there is no advantage in inducing further hypocapnia as this will only shift the oxygen dissociation curve further to the left, making oxygen less available to the tissues. When there is an acute rise in ICP, for example after an acute head injury ICP can be reduced by hyperventilation to lower arterial CO 2 tension. This technique is used during neurosurgery to reduce brain size to improve access for the surgeon.