Effects of sevoflurane on intracranial pressure and formation and absorption of cerebrospinal fluid in cats

The effects of sevoflurane on intracranial pressure (ICP) and the formation and absorption of cerebrospinal fluid (CSF) were examined in cats. Changes in ICP and superior sagittal sinus pressure (SSSP) were studied for 180 minutes during anesthesia with 1MAC sevoflurane (2.6%, inspired) and 50% N2O in O2. ICP increased significantly immediately after the start of anesthesia. The level remained for the subsequent 120 minutes, but increased significantly again 140 minutes after the start of anesthesia. There was no change in SSSP. The rate of CSF formation (Vf) was examined using the open ventriculocisternal perfusion method during anesthesia for 180 minutes with 1MAC sevoflurane or 1MAC enflurane (2.4%, inspired) and 50% N2O in O2. During sevoflurane administration, Vf decreased significantly 30 minutes after the start of anesthesia. In contrast, during enflurane administration, Vf increased significantly 10 minutes after the start of anesthesia. Finally, Vf and the rate of CSF absorption (Va) were measured under 1MAC sevoflurane or 1MAC enflurane and 50% N2O in O2 anesthesia, or under 50% N2O in O2 anesthesia. They were compared with ICP level. Vf decreased significantly when ICP level increased in all groups. The increase in Va when ICP level increased, was greater in the N2O group than in those anesthetized with sevoflurane or enflurane. The delayed increase of ICP under sevoflurane may have resulted in part from the cranial accumulation of CSF due to increased resistance to CSF absorption.