Degree of Sedation during Spinal Anesthesia in Healthy Volunteers. Pollock et al. (page 728)

In a two-part study, Pollock et al.  used Bispectral Index (BIS) monitoring to quantify the degree of sedation in unmedicated volunteers undergoing spinal anesthesia. In part I, a nonrandomized pilot study, researchers first determined baseline BIS measurements in 12 volunteers left for 10 min in a darkened room with soft music playing. Volunteers then received spinal anesthesia (50 mg lidocaine, 5%). BIS and additional monitoring, such as electrocardiography, blood pressure, and pulse oximetry, were continued at regular intervals during the study period. Block height and duration were assessed every 5 min for the first 30 mine and then at 10-min intervals until block resolution. Observer’s Assessment of Alertness/Sedation Scale (OAA/S) assessment was recorded every 5 min. The volunteers were also asked at the conclusion of the study to report their perceived degree of sedation.

In the second part of the study, 16 volunteers underwent baseline BIS monitoring and were then randomized to receive either placebo (sham injection) or 50 mg lidocaine, 5%, spinal anesthesia. Monitoring was similar to that in part I, with OAA/S being recorded every 10 min. Participants in part II were also asked to assess their perceived degree of sedation during spinal anesthesia.

Part I participants all had measurable sensory and motor blockade; median block height was T4 and mean duration of anesthesia to cold at S2 was 92 min. There was a statistically significant change from baseline in the BIS score progressively in all but three of the volunteers. The largest deviation from baseline occurred at 30 and 70 min after initiation of spinal anesthesia.

Two volunteers were excluded from final analysis of part II results: one for inadequate anesthesia and the other for hypotension and bradycardia. In volunteers receiving spinal lidocaine, median block height was T5, and mean duration of sensory analgesia to cold at S2 was 90 min. The largest difference in mean BIS scores was greatest at 65–75 min post–spinal injection. Although mean OAA/S and self-sedation scores showed strong correlation, BIS did not prove to be a sensitive measure of sedation in the randomized, blinded portion of this study.