Midlatency Auditory Evoked Potentials Predict Movements During Anesthesia with Isoflurane or Propofol

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Abstract
To determine threshold values, sensitivity, and specificity of midlatency auditory evoked potentials (MLAEP) for prediction of spontaneous intraoperative movements, 40 patients undergoing elective laparotomy were studied. Continuous epidural analgesia was used in all patients. To maintain general anesthesia, the patients in Group 1 (n = 20) received isoflurane (0.4-1.2 vol%), and the patients in Group 2 (n = 20) received propofol (3-5 mg x kg(-1) x h(-1) intravenously). Spontaneous movements were documented intraoperatively. Auditory evoked potentials were recorded continuously until the end of anesthesia. Latencies of the peaks V, Na, Pa, Nb, and P1 (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/P1 (microV) were measured. Changes of MLAEP latencies and amplitudes during anesthesia were similar in both groups. Anesthesia led to statistically significant increases in the latencies of Na, Pa, Nb, and P1 and decreases in the amplitudes of Na/Pa, Pa/Nb, and Nb/P1 compared with the awake state. Before and during spontaneous movement observed intraoperatively or during emergence from anesthesia, the latencies of the peaks Na, Pa, Nb, and P1 decreased, and the amplitudes Na/Pa, Pa/Nb, Nb/P1 increased significantly. A threshold value of 60 ms of Nb proved to be most predictive of movement during anesthesia. MLAEP recording seems to be a promising method to monitor the level of anesthesia as defined by spontaneous movement during anesthesia.