Isoflurane and cerebrospinal fluid pressure in neurosurgical patients

The effect of isoflurane on cerebrospinal fluid pressure (CSFP) was determined in 20 patients undergoing craniotomy for intracranial supratentorial neoplasm or hepatoma. In 15 of these patients, following endotracheal intubation, hyperventilation sufficient to result in PaCO2 25-30 torr was begun simultaneously with the introduction of 1 per cent isoflurane. In the remaining five patients ventilation was equivalent, but normocapnia was maintained by adding CO2 to the inspired gases. In the hypocapnic patients CSFPs did not increase above awake values (range 5-45 torr) following isoflurane administration. In the normocapnic patients (CSFPs consistently increased. In three of these five patients the increases were precipitous, but were corrected rapidly by establishment of hypocapnia. The authors conclude that the known cerebral vasodilator properties of isoflurance can be countered effectively by hypocapnia. Furthermore, unlike the situation with halothane, it is not necessary to establish hypocapnia prior to introducing isoflurane in order to avoid CSFP increases.