Effects of 1% and 2% enflurane on intracranial pressure in man

We have studied the effects of enflurane on intracranial pressure (ICP) in 9 neurosurgical patients, whose ICP was continuously monitored for therapeutic or diagnostic purposes. The control ICP was under 15 Torr in 5 cases, under 20 Torr in 3 cases and of 25 Torr in one case. In order to achieve stable ventilatory conditions, the patients were kept under controlled ventilation, breathing a mixture of 60 to 70% nitrous oxide and oxygen. The PaCO2 was kept constant, at the pre-study level. Mean arterial pressure (MAP) was maintained stable with the administration of fluids and/or a phenylephrine drip. Cerebral perfusion pressure (CPP) was calculated as the difference between MAP and mean ICP. After a control stabilization period of about one hour, enflurane was introduced in the circuit at successive concentrations of 1 and 2% during 20 to 30 minutes. In seven patients, enflurane did not produce any change of ICP. ICP rose only in 2 patients, whose control values were of 16 and 25 Torr. The overall changes, however, are not significant. There is a small significant decrease of MAP and CPP under 2% enflurane when compared to control, of probably no clinical importance (under 10% change). Our results do not show that enflurane is entirely without effect on ICP, but we think that 1 to 2% enflurane may be used in neuroanesthesia with a reasonable margin of safety, in association with slight hyperventilation and other means or reducing ICP, in accordance to clinical requirements.