Abstract: Objective To investigate application of different doses of mivacurium in infants and young children under combined intravenous-inhalational anesthesia. 
Methods A total of 120 children scheduled for surgery under general anesthesia at Hebei Children′s Hospital were selected. They were divided into group Ⅰ (aged 2 to 12 months) and group Ⅱ (aged 13 to 36 months) based on the age, and further randomly divided into subgroups based on the initial dose of mivacurium: 0.15 mg/kg and 0.2 mg/kg, resulting in subgroups Ⅰ0.15, Ⅰ0.2, Ⅱ0.15, and Ⅱ0.2, with 30 patients in each subgroup. The muscle relaxation-related indicators were observed and recorded, as well as the changes in heart rate (HR), mean arterial pressure (MAP), and blood oxygen saturation (SpO2) before the anesthesia induction and at 1, 3 and 5 min after the injection of mivacurium. 
Results Comparison of the onset time of the different dose of micuronium: compared with group Ⅰ0.15, the ThD75, ThD90, and ThDmax of group Ⅰ0.2 were obviously shortened (P＜0.05); compared with group Ⅱ0.15, the ThD75, ThD90, and ThDmax of group Ⅱ0.2 were obviously shortened (P＜0.05). Comparison of the onset time of mivacurium in different age groups: compared with group Ⅰ0.15, the ThD75, ThD90, and ThDmax of group Ⅱ0.15 were obviously prolonged (P＜0.05); compared with group Ⅰ0.2, the ThD75 and ThDmax of group Ⅱ0.2 were obviously prolonged (P＜0.05). There was no significant difference between the groups in Th, ThR25, ThR75, RI, TOFR75, TOFR90 and satisfaction rate of tracheal intubation (P＞0.05). There was no significant difference in interaction between groups, time points and time points between groups with respect to HR, MAP and SpO2 (P＞0.05). 
Conclusion The related factors affecting the neuromuscular blockade are the age of children and the first dose of mivacurium. Mivacurium (0.15 mg/kg, 0.2 mg/kg) applied in pediatric anesthesia is safe and effective. 

Key words: anesthesia, mivacurium, children, muscle relaxation