A comparison of SNAP II and bispectral index monitoring in patients undergoing sedation

Abstract

Clinical signs and patients' verbal responses have traditionally been used to assess patients' comfort and the depth of sedation. Recently, level-of-consciousness monitors have been used to guide sedation. The SNAP II(c) is a single-lead electroencephalogram device that displays a SNAP(c) Index - a derived value based on both high and low frequency electroencephalogram signals. Much of the current clinical research on monitoring during sedation involves the bispectral index monitor. We compared simultaneous readings recorded by the SNAP II and bispectral index during sedation in 51 consecutive patients undergoing surgery. The anaesthesia team was blinded to the SNAP II and bispectal index values. Concurrent SNAP II and bispectral index readings displayed similarly-shaped trajectories during sedation, but further studies are needed to establish the routine clinical utility of both these monitors.

Figure 1

Four selected patients’ data. SNAP II© and BIS trajectories are shown in the lower part of each set. The vertical axis shows the SNAPc and BIS Index scores while the horizontal axis represents the surgical procedure duration in minutes from initiation.

Figure 2

Individual minute-by-minute differences between SNAP II© and BIS cerebral monitor index scores for all study participants, grouped as follows: Panel A, short- (0–25 min); Panel B, medium- (25–40 min) and Panel C, extended- (≥ 40 min or more) duration surgery.