Modification of ketamine-induced intracranial hypertension in neurosurgical patients by pretreatment with midazolam.

The effect on intracranial pressure (ICP) of ketamine as an anaesthetic induction agent following pretreatment with either midazolam (ten cases) or diazepam (five cases) was investigated in unpremedicated neurosurgical patients. In all patients in the midazolam group, ICP increased following ketamine while the cerebral perfusion pressure (CPP) fell in five cases. ICP rose further after intubation by a mean of 21 mmHg (2.8 kPa) with a further drop in CPP in two cases. The changes were usually terminated after pethidine was given but were allowed to continue for 10 min or more in two cases. There was little increase in ICP after the diazepam-ketamine combination, while the CPP fell in one case and increased markedly in two cases. The mean increase in ICP following intubation was 6 mmHg (0.8 kPa) above control values. All patients required assisted ventilation after either benzodiazepine-ketamine combination. It is concluded that midazolam much more effectively suppresses the cardiostimulatory action of ketamine than the increase in ICP and that neither a midazolam-ketamine nor a diazepam-ketamine combination should be considered safe for use in patients who may have reduced intracranial compliance.