Effect of sevoflurane/nitrous oxide versus propofol anaesthesia on somatosensory evoked potential monitoring of the spinal cord during surgery to correct scoliosis

Background. Use of intraoperative somatosensory evoked potential (SSEP) monitoring is helpful in spinal corrective surgery but may be affected by anaesthetic drugs. An anaesthetic technique that has less effect on SSEP or allows faster recovery is an advantage. We compared the effects on SSEP and the clinical recovery profiles of sevoflurane/nitrous oxide and propofol anaesthesia during surgery to correct scoliosis. Methods. Twenty adolescent patients were randomized into two groups of 10. One group received sevoflurane-nitrous oxide anaesthesia and the other received propofol i.v. anaesthesia. An alfentanil infusion was used for analgesia in both groups. Results. Changes in anaesthetic concentration produced little effect on the latency of SSEP, but the effect on the variability of SSEP amplitude was significant (P<0.05). Sevoflurane produced a faster decrease in SSEP and a faster recovery than propofol (P<0.05). On emergence, patients who received sevoflurane tended to have shorter recovery times to eye opening (mean 5.1 vs 20.6 min, P=0.09) and toe movement (mean 7.9 vs 15.7 min, P=0.22). Those who had received sevoflurane were significantly more lucid and cooperative in recovery. Conclusions. Sevoflurane produces a faster decrease and recovery of SSEP amplitude as well as a better conscious state on emergence than propofol.