Effects of sustained Trendelenburg position on the spectral signatures of the EEG: implications for the consistency of the level of anesthesia, an observational study.

Measurements from level of anesthesia monitors can be influenced by various factors. This study aimed to compare the evolution of BIS Vista™ monitor and electroencephalogram (EEG) parameters over time during steep Trendelenburg positioning. In this prospective observational study, data were collected from patients undergoing robot-assisted radical prostatectomy. BIS Vista™ monitor parameters (BIS Index, SEF95, EEG-BIS) and a 4-electrode EEG setup (EEG-BrVis) were recorded at baseline, 30 min after Trendelenburg positioning, and every 60 min until procedure completion. Parameter changes from baseline and trends over time were analyzed. Eighteen patients were analyzed. The mean surgical duration was 269 ± 69 min, with Trendelenburg angles ranging from 32º to 41º. No significant changes were observed in BIS Index or SEF95 in trend over the time. Mean changes in BIS Index were 0.017 ± 0.01 (p = 0.096) and 0.016 ± 0.011 (p = 0.162); SEF95 changes were − 0.002 ± 0.002 Hz (p = 0.390) and − 0.002 ± 0.002 Hz (p = 0.326) for left and right hemispheres, respectively. However, the area under the curve of the power spectral (p < 0.001) and all frequency bands power (p < 0.001) showed a significant decrease over the time in both EEG. Minimal changes without clear pattern were observed in spectral slope during the study. BIS Index and SEF95 remained consistent during prolonged Trendelenburg positioning. The reduction in EEG singal power across 0–45 Hz caused a vertical shift in the power spectrum with minimal changes in its spectral profile. Facial tissue edema by positioning plays a primary role in the EEG signal power reduction.