The effect of isoflurane on cerebrospinal fluid pressure in patients undergoing neurosurgery

Ten patients with intracerebral tumours (TC) and 13 patients with subarachnoid haemorrhage (SAH) from a ruptured cerebral arterial aneurysm were studied before intracranial surgery, and during a 3-h postoperative period. Cerebrospinal fluid pressure (CSFP) determined by an intraventricular (TC group) or intraspinal (SAH group) catheter, and mean arterial blood pressure (MABP) were recorded under neurolept anaesthesia (control) followed by isoflurane inhalation. These two measurements were performed during normocapnia. A third measurement was made during hypocapnia, with unchanged isoflurane concentration. After the experimental period, isoflurane remained the main anaesthetic agent throughout the surgical procedure. After recovery from anaesthesia, the patients were monitored with CSFP and blood pressure during the first postoperative hours, and the quality of breathing was assessed by hourly blood-gas analyses. The results show that isoflurane causes a 10-14% reduction of MABP with no further changes during hyperventilation. Mean CSFP increased 27% in the TC group, and 12% in the SAH group after isoflurane induction and decreased from these levels by 29% during hyperventilation in both groups. Consequently, the impact on cerebral perfusion pressure (CPP) by isoflurane was a 19% and 21% mean decrease in the TC and SAH group, respectively. Controlled hyperventilation reduced this effect by partially restoring control CPP values, with 8% and 14% increase, respectively. In the postoperative follow-up, all patients had normal breathing and blood pressure with low values of CSFP. It is concluded that isoflurane can be used in intracranial surgery with adequate safety if combined with controlled hyperventilation.