Effect of ketamine on bispectral index during propofol--fentanyl anesthesia: a randomized controlled study

The Bispectral Index (BIS) helps in the assessment of the depth of hypnosis. N-methyl-D-aspartic acid antagonist, ketamine, has been used in various doses to decrease postoperative morphine consumption. The purpose of our study was to compare the effects of two different doses (0.5 mg/kg and 0.2 mg/kg) of ketamine on BIS values.

Forty-five ASA I or II patients undergoing general anesthesia were included in this double-blind, prospective, control trial and randomly allocated into three groups. After induction of anesthesia and tracheal intubation, a propofol infusion was started and titrated to attain BIS values of around 40. After five minutes of stable BIS values and in the absence of any surgical stimulus, patients received either 0.5 mg/kg of ketamine (Group K1) or 0.2 mg/kg of ketamine (Group K2) or normal saline (Group N) as bolus intravenously. BIS values were recorded for the next 15 minutes, at five-minutes interval.

Mean BIS values were significantly increased in Group K1 (63.5) while Group K2 (42.0) failed to show any significant rise. BIS values in Group K2 were comparable to those in Group N.

Thus, under stable propofol anesthesia, a bolus ofketamine 0.5 mg/kg increases BIS values while ketamine 0.2 mg/kg does not.