Comparison of effects of dexmedetomidine and fentanyl on median effective concentration of propofol required for inducing respiratory depression / 中华麻醉学杂志

ABSTRACT

Objective To compare the effects of dexmedetomidine and fentanyl on the median effective concentration (EC50) of propofol required for inducing respiratory depression.Methods ASA physical status Ⅰ or Ⅱ patients,aged 30-50 yr,weighing 50-75 kg,with body mass index of 22-28 kg/m2,scheduled for elective gynecological surgery under general anesthesia,were randomly divided into 3 groupscontrol group (group C),dexmedetomidine group (group D) and fentanyl group (group F).Dexmedetomidine 0.5 μg/kg and fentanyl 1.5 μg/kg in 10ml of normal saline were infused over 10 min in D and F groups,respectively,while the equal volume of normal saline was given in group C.Lidocaine was injected intravenously followed by target-controlled infusion of propofol.In C,D and F groups,the initial target concentration of propofol was 2.5,2.1 and 1.1 μg/ml,respectively,and the ratio between the two successive concentration gradients was 1.1.It was defined as positive when patients developed respiration depression.EC50 and 95％ confidence interval of propofol inducing respiratory depression were calculated.BIS values and OAA/S scores were recorded after admission to operating room (T0),after infusion of dexmedetomidine,fentanyl or normal saline,at 5 and 10 min after the start of propofol target-controlled infusion and after the target effect-site and plasma concentrations were balanced.Results EC50 (95％ confidence interval) of propofol required for inducing respiratory depression was 2.72 (2.55-2.91),2.15 (2.05-2.27)and 1.17(1.08-1.25) μg/ml in C,D and F groups,respectively.Compared with group C,the EC50 was significantly decreased in D and F groups and the BIS values and OAA/S scores were increased in group F (P ＜ 0.05),and no significant changes were found in the BIS values and OAA/S scores in group D (P ＞ 0.05).The EC50 was significantly decreased and the BIS values and OAA/S scores was increased in group F as compared with group D (P ＜ 0.05).When the BIS values reached 65 or OAA/S scores was 3,the effect-site concentration was significantly lower in D and F groups than in group C (P ＜ 0.05).In C,D and F groups,the percentage of patients who developed upper airway obstruction caused by glossocoma was 100％,60％ and 20％,respectively,and who developed decreased respiratory rate or apnea (RR≤ 8 bpm or respiratory arrest time≥ 15 s) was 0,40％ and 80％,respectively.Conclusion Although dexmedetomidine induces no respiratory depression,dexmedetomidine can enhance the potency of propofol required for inducing respiratory depression and the prtency is lower than that of small-dose fentanyl.