Midlatency auditory-evoked potentials in the assessment of sedation in cardiac surgery patients

Abstract

Objectives: Midlatency auditory-evoked potentials (MLAEPs) may provide an objective measure of depth of sedation. The aim of this study was to evaluate MLAEPs for measuring sedation in cardiac surgery patients. Design: Prospective study. Setting: Intensive care unit of a university hospital. Participants: Twenty-two patients scheduled for elective coronary artery bypass grafting. Interventions: MLAEPs were obtained at 5 time points: the day before surgery (baseline), 1 hour before surgery, after premedication, postoperatively during deep (Ramsay 6) and moderate (Ramsay 4) sedation, and the day after surgery. Measurements and Main Results: The latency of the Nb MLAEP component increased from 44 ms (38–60 ms; median, range) at baseline to 49 ms (41–64 ms) after premedication ( p = 0.03) and further to 63 ms (48–80 ms) during deep sedation after surgery ( P < 0.01). Although a decreasing clinical level of sedation after rewarming was not associated with a significant change in Nb latency (61 ms [42–78 ms]), the MLAEP NaPa amplitude increased from 0.9 μV (0.4–1.6 μV) to 1.3 μV (0.8–3.9 μV; p = 0.01). Nb latency remained increased the day after surgery (49 ms [37–71 ms]) as compared with baseline ( p < 0.01). Conclusions: MLAEP latencies can reflect subtle changes in auditory perception, while amplitudes seem to change with transition between deep levels of sedation.