Effect Of Dexmedetomidine And Midazolam On Median Effective Concentration Of Propofol For Respiratory Depression In Aged Patients

Objective To investigate dexmedetomidine and midazolam for the effect on the median effective concentration (EC50) of propofol for respiratory depression in aged patients.Methods ASA Ⅰ or Ⅱ grade patients, aged65～80years, scheduled for lower limb surgery under epidural anesthesia were randomly allocated to3groups:group D received0.4μg/kg dexmedetomidine, group M received0.03mg/kg midazolam and group C received10ml sodium chloride. The propofol TCI was started after infusing the experimental medicine. The target plasma concentration of the first patient in group D was set to1.4μg/ml,1.2μg/ml in group M and2.2μg/ml in group C. The following patient’s target plasma concentration was determined based on the reaction of respiratory depression in the previous patient. The ratio of the adjacent target concentration was1.1.Results EC50of propofol TCI for respiratory depression was1.64μg/ml (95%CI was1.52～1.78μg/ml) in group D,1.18μg/ml (95%CI was1.15～1.21μg/ml) in group M and2.35μg/ml (95%CI was2.19-2.51μg/ml) in group C. The EC50was lower in group D and M than that in group C, and it was lower in group M than in group D.Conclusion Both dexmedetomidine and midazolam can decrease the EC50of propofol TCI for respiratory depression in aged patients. The extent of reduction in the EC50of propofol caused by dexmedetomidine is significantly smaller than midazolam.