Objective:To determine the optimum dose of dexmedetomidine for prevention of emergence agitation after sevoflurane anesthesia in children undergoing ambulatory surgery. Methods:Twenty-two ASA Ⅰor Ⅱ children of both sexes aged 2-7 years undergoing elective dental repair under sevoflurane anesthesia were studied. Laryngeal mask airway（LMA） was inserted after induction of anesthesia with inhalation of 8% sevoflurane by mask. Dexmedetomidine was intravenous infused for 10 minutes to prevent emergence agitation after LMA insertion. The dose of dexmedetomidine was determined by using Dixon’s up-and-down method（increment or decrement of 0.1 μg/kg）. The initial dose of dexmedetomidine was 0.5 μg/kg. Anesthesia was maintained with 2%

4

% sevoflurane and spontaneous breathing was maintained throughout the surgery. Sevoflurane inhalation was terminated at the end of surgery. The Pediatric Anesthesia Emergence Delirium Scale（PAED）was used to assess emergence agitation. The PAED score was recorded every 5 minutes within 30 minutes after surgery. And the max score more than ten was considered emergence agitation. The modified Children’s Hospital of Eastern Ontario Pain Scale（m-CHEOPS）score was recorded immediately after recovery（T0）

and 10 and 20 minutes（T1

T2）after recovery for evaluating the pain degree. The ED50

ED95 and 95% confidence interval（CI）of dexmedetomidine for prevention of emergence agitation were calculated. Results:The m-CHEOPS score was significantly increased at T0 in emergence agitation group than in no emergence agitation group（P

<

0.05）. There was no significant difference between the two groups in m-CHEOPS score at T1

2

（P

>

0.05）. There was no significant difference between the two groups in terms of age

weight

height

operation time and emergence time（P

>

0.05）. The ED50 of dexmedetomidine for prevention of emergence agitation after sevoflurane anesthesia in children undergoing ambulatory surgery was 0.58 μg/kg（95%CI=0.43 to 0.73 μg/kg）. ED95was0.78 μg/kg（95%CI=0.67 to 2.27 μg/kg）. Conclusion:The ED50 and ED95of dexmedetomidine for prevention of emergence agitation after sevoflurane anesthesia in children undergoing ambulatory surgery are 0.58 μg/kg and 0.78 μg/kg respectively.