The influence of ketamine on both normal and raised intracranial pressure of artificially ventilated animals.

The effect of two different doses of ketamine, 0.5 mg kg-1 body weight, and 2.0 mg kg-1 body weight, on intracranial pressure and cerebral perfusion pressure were investigated in 21 young pigs (26-34 kg) under controlled artificial ventilation. Three groups each containing seven animals were studied: Group 1. Initially normal blood pressure and an intracranial pressure within the normal range (10.7 mmHg). Group 2. Normal blood pressure and increased intracranial pressure caused by inflating an epidural balloon (29.2 mmHg). Group 3. Increased intracranial pressure (32.7 mmHg) and mean arterial pressure reduced by approximately 30% through controlled haemorrhage. There was no increase in intracranial pressure from either normal or initially increased values. This applied to animals with normal blood pressure values and also to those in haemorrhagic shock. This observation can be explained by the lack of an increase in PCO2 under controlled ventilation. During haemorrhagic shock cerebral perfusion pressure fell significantly as a result of the fall in mean arterial pressure. This particularly applied to the 2.0 mg kg-1 dose of ketamine. We therefore consider volume substitution to be essential in this situation.