Effects of propofol, propofol nitrous oxide and midazolam on cortical somatosensory evoked potentials during sufentanil anaesthesia for major spinal surgery

Recording of cortical somatosensory evoked potentials (CSEP) enables monito ring of spinal ford function. We studied the effects of propofol, propofol- nitrous oxide or midazolam during sufentanil anaesthesia on CSEP monitoring during major spinal surgery. Thirty patients with normal preoperative CSEP were allocated randomly to one of the following anaesthesia regimens: prop ofol (2.5 mg kg(-1) followed by 10-6 mg kg(-1) h(-1)) with or without nitro us oxide, or midazolam (0.3 mg kg(-1) followed by 0.15 mg kg(-1) h(-1)) com bined with sufentanil 0.5 mu g kg(-1) h(-1) in the propofol and midazolam g roups, or 0.25 mu g kg(-1) h(-1) in the propofol-nitrous oxide group. CSEP were elicited by alternate right and left tibial posterior nerve stimulatio n and recorded before and after induction (15 min, 1, 2 and 3 h), and durin g skin closure. CSEP latencies were not significantly modified in the three groups. CSEP amplitude decreased significantly in the propofol-nitro-us ox ide group (from mean 2.0 (SEM 0.3) to 0.6 (0.1) mu V; P<0.05) but not in th e propofol (from 1.8 (0.6) to 2.2 (0.3) mu V) or midazolam (1.7 (0.5) to 1. 6 (0.5) mu V) groups. The time to the first postoperative voluntary motor r esponse (recovery) delay was significantly greater in the midazolam group ( 115 (19) min) compared with the propofol and propofol-nitrous oxide groups (43 (8) and 41 (3) min, respectively). Consequently, the use of propofol wi thout nitrous oxide can be recommended during spinal surgery when CSEP moni toring is required.