Abstract: Objective To investigate the effects of different infusion rate of remifentanil infusion on spontaneous ventilation in children who received sevoflurane anesthesia. Methods: A total of 120 children ,aged 3-6 years,undergoing strabismus surgery were assigned to 4 groups at random(n=30):C group(administration of saline),L group(remifentanil 0.03μg?kg-1?min-1), M group(remifentanil 0.06μg?kg-1?min-1) and H group(remifentanil 0.09μg?kg-1?min-1).The mean blood pressure,heart rates and respiratory rates,tidal volime,minute ventilation,and endtidal CO2, endtidal SEV were recorded after laryngeal mask insertion(T1), an initial bolus dose of remifentanil(T2),10mins after remifentanil infusion(T3),15mins after remifentanil infusion(T4), laryngeal mask remove(T5) respectively.The adverse events and time of induction,maintainance and emergence were also recoded. Results: There was no significant difference in general description , MBP, HR and VT in four groups.There was no body movement and desaturation observed. The RR and MV of H group at T3 and T4 were lower than other groups significantly(P<0.05) while PETCO2 were higher. The RR and MV between M and L group were not significantly different but lower than that of C group. Conclusions: Remifentanil infusion at a rate of 0.03～0.09μg?kg-1?min-1 could depress spontaneous ventilation in children who received sevoflurane anesthesia,but rarely lead to desaturaton.The respiratory depression effect is mainly manifested by reduction of RR rather than MV,especially at the rate of 0.09μg?kg-1?min-1..It is a good option to choose the low or moderate dose of remifentanil infusion to keep spontaneous ventilation in children while avoiding severe respiratory depression according to the demand of operations.

Key words: remifentanil, Sevoflurane, Spontaneous ventilation, Anesthesia, Pediatric