EFFECTS OF KETAMINE ON CEREBRAL BLOOD-FLOW VELOCITY IN HUMANS - INFLUENCE OF PRETREATMENT WITH MIDAZOLAM OR ESMOLOL

During normoventilation and ''light'', haemodynamically stable, steady -state anaesthesia with isoflurane 0.3%, the effect of ketamine intrav enously was investigated in 24 patients randomly assigned to one of th e following groups: group 1 (control group) no ketamine, group 2 (keta mine group) ketamine 2mg.kg(-1), group 3 (ketamine/midazolam group) ke tamine 2mg.kg(-1) after pretreatment with midazolam and group 4 (ketam ine/esmolol group) ketamine 2mg.kg(-1) while maintaining mean arterial blood pressure at a preketamine level with esmolol. Ketamine-induced cerebrovascular changes were measured by means of transcranial Doppler ultrasonography. Control readings in patients without ketamine challe nge demonstrated stable cardiovascular and cerebrovascular baseline co nditions. Cerebral blood flow velocity and mean arterial blood pressur e, however, significantly increased after administration of ketamine w ithout pretreatment. The increase in cerebral blood flow velocity coul d not be blocked by maintaining mean arterial blood pressure at baseli ne value with esmolol. In contrast, the effects of ketamine on cerebra l blood flow velocity and mean arterial blood pressure were prevented by prior administration of midazolam. The results suggest that ketamin e may significantly influence intracerebral haemodynamics via a drug e ffect rather than via a secondary effect due to changes in arterial ca rbon dioxide and/or mean arterial blood pressure.