INTRACRANIAL-PRESSURE, MIDDLE CEREBRAL-ARTERY FLOW VELOCITY, AND PLASMA INORGANIC FLUORIDE CONCENTRATIONS IN NEUROSURGICAL PATIENTS RECEIVING SEVOFLURANE OR ISOFLURANE

This study examined the concentration-related effects of sevoflurane a nd isoflurane on cerebral physiology and plasma inorganic fluoride con centrations. Middle cerebral artery flow velocity (V-mca), int acrania l pressure (ICP), electroencephalogram (EEG) activity, and jugular bul b Venous oxygen saturation were measured, and cerebral perfusion press ure (CPP) and estimated cerebral vascular resistance (CVRe) were calcu lated at baseline and at 0.5, 1.0, and 1.5 minimum alveolar anesthetic concentration (MAC) sevoflurane (n = 8) or isoflurane (n = 6). Mannit ol 0.5-0.75 g/kg was given before dural incision, and blood was sample d for plasma inorganic fluoride during surgery and for up to 72 h post operatively. Both sevoflurane and isoflurane decreased V-mca (to 31 +/ - 12 - 36 +/- 14 cm/s, mean +/- SD), did not significantly alter ICP ( 13 +/- 9 - 15 +/- 11 mm Kg), and did not cause epileptiform EEG activi ty. With sevoflurane, decreased V-mca was accompanied by decreased CPP and unchanged CVRe at 0.5 MAC, and unchanged CPP and increased CVRe a t 1.0 and 1.5 MAC. Plasma inorganic fluoride was 39.0 +/- 12.9 mu M at the end of anesthesia (3.2 +/- 2.0 MAC hours) with sevoflurane, simil ar to the value (36.2 +/- 3.9 mu M) for 3.7 +/- 0.1. MAC hours sevoflu rane in patients not receiving mannitol. Decreased V-mca during sevofl urane presumably results from decreased cerebral metabolic rate, with CVRe changing secondarily in accord with CPP. Plasma inorganic fluorid e does not seem to be altered by mannitol-induced diuresis. Implicatio ns: In neurosurgical patients, sevoflurane decreased middle cerebral a rtery flow velocity and caused no epileptiform electroencephalogram ac tivity and no increase of intracranial pressure or plasma inorganic fl uoride. These effects are suitable for neurosurgery. Two other possibl e effects of sevoflurane, i.e., increased cerebrospinal fluid volume a nd/or intracranial elastance, may not be suitable for neurosurgery and warrant further study.