• Satoki Inoue, Masahiko Kawaguchi, Shimoda Takashi, Meiko Kakimoto, Takanori Sakamoto, Katsuyasu Kitaguchi, Hitoshi Furuya, Tetsuya Morimoto, and Toshisuke Sakaki.
• Department of Anesthesiology, Nara Medical University, Kashihara, Nara, Japan. seninoue@nmu-gw.naramed-u.ac.jp
• Spine. 2002 Nov 1;27(21):E454-9.

Study DesignMotor-evoked potentials from the external anal sphincter were analyzed using transcranial electrical stimulation during spinal surgery in patients under general anesthesia.ObjectiveTo investigate whether motor-evoked potentials from the external anal sphincter could be elicited by transcranial electrical stimulation under general anesthesia.Summary Of Background DataLumbosacral surgery often places nerve rootlets at risk for injury during operative dissection. Specifically, injury for sacral rootlets can result in bowel and bladder dysfunction, but the techniques for monitoring bowel and bladder function are limited.MethodsThirty patients who underwent elective spinal surgery were studied. Patients were anesthetized with 50% nitrous oxide in oxygen, fentanyl, and 4 mg/kg/h of propofol (n = 19) or 1 mg/kg/h of ketamine (n = 11). The level of neuromuscular blockade, assessed by recording the M-response from the right abductor pollicis brevis muscle, was maintained at an M-response amplitude of 40-50% of control. Motor-evoked potentials in response to a multipulse transcranial electrical stimulation at stimulus sites of C3-C4 or Fz-Cz were recorded from the skin over the subcutaneous part of the external anal sphincter using a plug-type electrode probe. The success rate of motor-evoked potentials' recording and peak-to-peak amplitude and the onset latency of motor-evoked potentials were evaluated.ResultsSuccess rates of motor-evoked potentials from the external anal sphincter were 73% and 53% after transcranial stimulation at stimulus sites of C3-C4 and Cz-Fz, respectively. Amplitudes of motor-evoked potentials after C3-C4 stimulation were significantly greater than those after Cz-Fz stimulation. Motor-evoked potential latency from the external anal sphincter was 18.6 +/- 1.5 and 19.0 +/- 2.7 msec after C3-C4 and Cz-Fz stimulation, respectively.ConclusionsThe results suggest that, using a transcranial multipulse stimulation, monitoring of motor-evoked potentials from the external anal sphincter is feasible during ketamine- and propofol-based anesthesia. However, further improvement of techniques would be required for intraoperative elicitation of motor-evoked potentials from the external anal sphincter.

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