The Effects Of Spinal Anesthesia On ED₅₀ And BIS₅₀ Of Etomidate For Loss Of Consciousness

Objective The aim of this study was to determine the median effective dosage(ED₅₀)of etomidate for LOC and the BIS value of etomidate for LOC of 50%patients(BIS₅₀)and to investigate the effects of spinal anesthesia on the ED₅₀ and BIS₅₀0 of etomidate for LOC.Methods This is a prospective,randomized controlled sequential study.Forty-six patients scheduled for elective gynecological operations were randomly allocated to two groups to receive either etomidate alone?group E,n=26?or etomidate combined with spinal anesthesia?group ES,n=20?.Patients in the group ES received spinal anesthesia?3ml of 0.5%hyperbaric bupivacaine?before injection of etomidate.The first patient in group E received 0.089mg/kg of etomidate,and the first patient in group ES received 0.076mg/kg of etomidate 15 minutes after spinal anesthesia.The dosage of etomidate required for next patient was determined by up-and-down method in the two groups.The ED₅₀ and BIS₅₀ of etomidate for LOC were determined by the Bliss method and the isotonic regression method.The bootstrap approach was used to estimate the 83%confidence interval?83%CI?of ED₅₀ and BIS₅₀.Results There were no significant differences between the two groups in patient's age,height,weight,ASA physical status,SpO₂ and BIS measurements at baseline?both P>0.05?;The ED₅₀ of etomidate for LOC was 0.103mg/kg?95%CI,0.092-0.115mg/kg?in group E and0.082mg/kg?95%CI,0.075-0.090mg/kg?in group ES by the Bliss method,and the BIS₅₀ was59?95%CI,55-63?in group E and 69?95%CI,62-76?in group ES.The ED₅₀ of etomidate for LOC was 0.105 mg/kg?83%CI,0.100-0.110 mg/kg?in group E by the isotonic regression method and bootstrap approach,which was significantly higher than the 0.083mg/kg?83%CI,0.080-0.087 mg/kg?in group ES?P<0.05?;The BIS₅₀ was 46?83%CI,41-48?in group E,which was significantly lower than the 56?83%CI,51-62?in group ES?P<0.05?;The MAP and HR values at baseline between the two groups were not statistically different?both P>0.05?.The MAP at 1min,2min,3min,5min after injection of etomidate and the HR at 1min,3min after injection of etomidate were significantly decreased in group ES compared to group E?P<0.05?.Conclusion The spinal anesthesia can significantly reduce the ED₅₀ of etomidate for LOC and enhance the sedative effect of etomidate.The spinal anesthesia can significantly affect the BIS value of etomidate for LOC.