Optimum dose of dexmedetomidine when combined with propofol for induction of anesthesia

Objective To investigate the optimum dose of dexmedetomidine when combined with propofol for induction of anesthesia.Methods One hundred and twenty ASA physical status Ⅰ or 1Ⅱ patients of beth sexes,aged 18-60 yr,with body mass index of 18.5-30.0 kg/m2,scheduled for elective ophthalmologic operation under general anesthesia,were randomly divided into 6 groups (n =20 each) using a random number table:normal saline group (NS group) and different doses of dexmedetomidine groups (D1-D5 groups).Different loading doses of dexmedetomidine 0.2,0.4,0.6,0.8 and 1.0 μg/kg (in normal saline 50 ml) were infused intravenously in D1-D5 groups,respectively.The equal volume of normal saline was infused over 15 min in group NS.After 10 min observation,target-controlled infusion (TCI) of propofol was started.The initial target plasma concentration was set at 3.2 μg/ml.Loss of consciousness was considered to be positive response.The median effective concentration (EC50) and 95％ confidence interval of propofol TCI required for loss of consciousness were calculated.After administration of dexmedetomidine,the development of adverse effects was recorded before propofol TCI.Results Compared with NS group,the EC50 of propofol TCI required for loss of consciousness was significantly decreased in D2-D5 groups,and no significant change was found in the EC50 of propofol TCI required for loss of consciousness in D1 group.The EC50 of propofol TCI was decreased gradually with the increasing doses of dexmedetomidine between D1 and D2 groups,between D2 and D3 groups,and between D4 and D5 groups,while there was no significant difference in the EC50 of propofol TCI required for loss of consciousness between D3 and D4 groups.The incidence of hypotension was 5％ (D3 group),11％ (D4 group) and 31％ (D5 group),and the incidence of bradycardia was 0 (D3 group),11％ (D4 group),and 19 ％ (D5 group).No hypotension and bradycardia developed in D1 and D2 groups.The incidence of hypotension and bradycardia was significant increased in D4 and D5 groups as compared with NS,D1,D2 and D3 groups.Conclusion The optimum dose of dexmedetomidine is 0.4μg/kg when combined with propofol for induction of anesthesia. Key words: Dexmedetomidine ;  Dose-response relationship, drug;  Propofol