Influence of high-dose opioid anesthesia on posterior tibial nerve somatosensory cortical evoked potentials: Effects of fentanyl, sufentanil, and alfentanil

The effects of high doses of fentanyl (group F), sufentanil (group S), and alfentanil (group A) on posterior tibial nerve somatosensory cortical evoked potentials were studied in 30 patients scheduled for elective valve replacement surgery. Anesthesia was induced with either fentanyl, 75 μg/kg, sufentanil, 5 μg/kg, or alfentanil, 125 μg/kg. The lungs were ventilated with oxygen/air. A bolus dose of fentanyl, 25 μg/kg, was given 30 minutes after induction of anesthesia in group F. Anesthesia was maintained with a continuous infusion of sufentanil, 5μg/kg/h, in group S, or alfentanil, 500 μg/kg/h, in group A. Latencies of the peaks of the primary cortical complex (P1, N1, 132) increased by 1 to 2 ms after induction of anesthesia, although this was significant (P < 0.01) only for P1 and N1 in groups F and S. N2 latency increased significantly (P < 0.01) by 6 to 10 ms in all groups. P1-N1 amplitude did not change after induction of anesthesia. N1-P2 amplitude decreased significantly (P < 0.01) to 60%-70% of preinduction values in groups F and S. P2-N2 amplitude decreased significantly (P < 0.01) to 60%-70% of preinduction values in all groups. P1, N1 and P2 latencies did not change significantly from the post-induction values in the period preceding cardiopulmonary bypass (75 ± 16 minutes) in groups F and S. In group A significant changes were observed only for N1 and P2 latency (P < 0.01). During this period there was a further gradual increase in N2 latency and amplitudes remained stable, except P1-N1 amplitude in group F, which decreased significantly (P < 0.05). A bolus dose of fentanyl, 25 μg/kg, given in group F at 30 minutes after induction of anesthesia did not change latencies and amplitudes. No significant differences in latency or amplitude were found at any time among the three study groups. It is concluded that anesthesia with high doses of fentanyl, sufentanil, or alfentanil is a suitable technique when intraoperative monitoring of posterior tibial nerve somatosensory cortical evoked potentials is indicated.