Desflurane and isoflurane improve neurological outcome after incomplete cerebral ischaemia in rats

We have investigated the effects of isoflurane and desflurane on neurologic al outcome in a rat model of incomplete cerebral ischaemia. We studied 40 n on-fasted male Sprague-Dawley rats, anaesthetized, intubated and ventilated mechanically with isoflurane and nitrous oxide in oxygen (FIO2 0.3). Arter ial and venous catheters were inserted for measurement of arterial pressure , drug administration and blood sampling. A biparietal electroencephalogram (EEG) was recorded continuously using subdermal platinum electrodes. At co mpletion of surgery, administration of isoflurane was discontinued (with th e exception of those animals receiving isoflurane as treatment) and rats we re allowed an equilibration period of 30 min according to the following pro cedure: group I (n = 10), 66% nitrous oxide in oxygen and fentanyl (bolus 1 0 mu g kg(-1) i.v. followed by infusion at a rate of 25 mu g kg(-1) h(-1)); group 2 (n = 10), 1.0 MAC of isoflurane in oxygen (FIO2 0.3) and air; grou ps 3 and 4 (n = 10 per group), 1.0 MAC or 1.5 MAC of desflurane in oxygen ( FIO2 0.3) and air, respectively. Ischaemia was produced by combined unilate ral common carotid artery ligation and haemorrhagic hypotension to 35 mm Hg for 30 min. Functional neurological deficit was evaluated for 3 days after cerebral ischaemia. At baseline, brain electrical activity was higher with fentanyl-nitrous oxide, 1.0 MAC of isoflurane and 1.0 MAC of desflurane (g roups 1-3) compared with 1.5 MAC of desflurane (group 4). Neurological outc ome was improved in isoflurane and desflurane anaesthetized animals (groups 2-4), regardless of the concentration used compared with fentanyl-nitrous oxide anaesthesia (group 1). The increase in plasma epinephrine and norepin ephrine concentrations during ischaemia was significantly higher in fentany l-nitrous oxide anaesthetized animals (group 1) compared with animals who r eceived volatile anaesthetics (groups 2-4). These data suggest that cerebra l protection produced by isoflurane and desflurane appears to be related to reduction in sympathetic activity rather than suppression of cerebral meta bolic rate.