MIDLATENCY AUDITORY-EVOKED POTENTIALS PREDICT MOVEMENTS DURING ANESTHESIA WITH ISOFLURANE OR PROPOFOL

To determine threshold values, sensitivity, and specificity of midlate ncy auditory evoked potentials (MLAEP) for prediction of spontaneous i ntraoperative movements, 40 patients undergoing elective laparotomy we re studied. Continuous epidural analgesia was used in all patients. To maintain general anesthesia, the patients in Group 1 (n = 20) receive d isoflurane (0.4-1.2 vol%), and the patients in Group 2 (n = 20) rece ived propofol (3-5 mg.kg(-1).h(-1) intravenously). Spontaneous movemen ts were documented intraoperatively. Auditory evoked potentials were r ecorded continuously until the end of anesthesia. Latencies of the pea ks V, Na, Pa, Nb, and P1 (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/P1 ( mu V) were measured. Changes of MLAEP latencies and amplitudes during anesthesia were similar in both groups. Anesthesia led to statisticall y significant increases in the latencies of Na, Pa, Nb, and P1 and dec reases in the amplitudes of Na/Pa, Pa/Nb, and Nb/P1 compared with the awake state. Before and during spontaneous movement observed intraoper atively or during emergence from anesthesia, the latencies of the peak s 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 b e most predictive of movement during anesthesia. MLAEP recording seems to be a promising method to monitor the level of anesthesia as define d by spontaneous movement during anesthesia.