The effects of isoflurane and propofol on intraoperative neurophysiological monitoring during spinal surgery

Abstract

To compare the effects of isoflurane and propofol on intraoperative neurophysiological monitoring (IONM) during spinal surgery. Thirty-five patients were randomly assigned to receive isoflurane (n = 17) or propofol (n = 18) anesthesia. Somatosensory evoked potentials (SEPs) following posterior tibial nerve stimulation were recorded before induction as baselines. Isoflurane concentrations and propofol infusions were adjusted to obtain four pre-determined BIS ranges: 65-55, 55-45, 45-35 and 35-25. For each range, a stable state was maintained for at least 10 min to perform IONM. The SEP latency P40 and amplitude P40-N50, the onset latency and amplitude of transcranial motor evoked potentials (tcMEPs), and threshold intensity of triggered electromyographic activity (EMG) following pedicle screw stimulation were statistically analyzed. Compared with baseline values, P40 latency increased and P40-N50 amplitude decreased after anesthesia with isoflurane or propofol. Isoflurane caused a dose-dependent depression of SEPs, but propofol did not. TcMEPs were recordable and stable in all patients receiving propofol in each BIS range, but only recordable in 10 (58.8%) receiving isoflurane with BIS >55, and 3 (17.8%) with BIS <55. No difference was noted in triggered EMG. Isoflurane inhibited IONM more than propofol. Propofol is recommended for critical spinal surgery, particularly when motor pathway function is monitored.