Evaluating the Use of 0.5 and 0.75 MAC Desflurane in Patients Undergoing Spinal Surgery

Background: Somatosensory- (SSEPs) and motor-evoked potentials (MEPs) are commonly used as an intraoperative neurophysiologic monitoring tool to detect aberrations to the spinal cord integrity during spinal surgery. Inhalational anaesthetic agents have a significant influence on evoked potentials by suppressing the amplitude and prolonging the latency. Evidences suggest that total intravenous anaesthesia (TIVA) is superior to inhalation anaesthesia for neuromonitoring in spinal surgery, and support the use of up to 0.5 minimum alveolar concentration (MAC) of inhalational anaesthetic agents in these procedures. Methods: Patients undergoing spinal surgeries will be prospectively recruited and be induced with TIVA at baseline of the evoked potentials. They will be randomized to receive balance anaesthesia with A) Desflurane MAC 0.5+remifentanil, or B) Desflurane MAC 0.75+remifentanil until the end of surgery. Influence of 1.0 MAC desflurane on the evoked potentials after the completion of surgery will also be studied. Desired Results: Endpoints include the changes to the amplitude and latency of SSEPs and MEPs with 0.5 and 0.75 MAC desflurane. The findings will indicate the safety of desflurane at the studied concentrations for spinal surgeries, and substantial savings with the use of desflurane instead of TIVA.