Hypnotic interaction between midazolam and ketamine during induction of general anesthesia

ObjectiveTo study the hypnotic interaction between midazolam and ketamine during induction of general anesthesia.MethodsNinety patients undergoing were randomly divided into three groups with 30 cases each.Anesthesia was induced with midazolam(group M),ketamine(group K) or midazolam plus ketamine (group M-K).The ratio of midazolam to ketamine in group M-K was 1:10.Before induction,each group received different doses of drugs by sequential methods.Failling to respond to verbal orders was regarded as the start-point of hypnotic effect,which was evaluated 2 minutes after drug administration.The ED50s of midazolam,ketamine and M-K combination for hypnotic effect were measured by sequential methods.Isobologram was drawn to analyze hypnotic interactions between midazolam and ketamine.ResultsThe ED50 for hypnotic effect was 0.18 mg/kg in group M(95% CI 0.09-0.31 mg/kg),0.50 mg/kg in group K(95% CI 0.38-0.61 mg/kg),and 0.038/0.38 mg/kg in group C(95% CI 0.024/0.24-0.073/0.73 mg/kg).The deviation of the location of ED50 of M-K combination from the connecting line was not statistically significant.ConclusionThe hypnotic interaction between midazolam and ketamine was additive,confirmed by isobolographic analysis.