Effect of bispectral index monitoring on sevoflurane consumption

The bispectral index, a parameter derived from the electroencephalograph, has been shown to correlate with the loss of consciousness and sedation. This study was designed to assess the effects of bispectral index monitoring on sevoflurane and its recovery profiles.

Sixty ASA I and II patients undergoing open abdominal surgery were randomized into two groups: one monitored using the bispectral index (Group BIS) and the other without its use (controls). After a standardized induction, anaesthesia was maintained with sevoflurane in both groups. In Group BIS, sevoflurane was titrated to maintain the bispectral index in the range 40-60. In the control group, the administered sevoflurane concentration was adjusted according to the signs of anaesthesia. The end-tidal sevoflurane concentration, bispectral index and routine haemodynamic variables were noted every 5 min during surgery. The consumption of sevoflurane was computed. At the conclusion of surgery operations, the time to 'open eyes on verbal command', 'motor response to verbal command' and Aldrete's score were recorded by a blinded anaesthesiologist.

The difference in the consumption of sevoflurane was not significant between the groups. Bispectral index monitoring was associated with a reduction of 4.73% in sevoflurane usage and 2.19 mL h(-1) was saved.

Bispectral index monitoring during anaesthesia provides only a small advantage related to the need to monitor the depth of anaesthesia.