Abstract: Objective  To evaluate the effects of dexmedetomidine on apoptosis of polymorphonuclear neutrophils and nuclear factor-κB（NF-κB） activity in peripheral blood in pediatric patients undergoing cardiopulmonary bypass. 
Methods  Sixty pediatric patients，of American Society of Anesthesiologists（ASA） physical statusⅡ or  Ⅲ，scheduled for elective repair of ventricular septal defect under continuous blood purification（CPB）, were randomly divided into 2 groups(n=30 each) using a random number table：control group(group C) and dexmedetomidine groups(group D)．In group D， dexmedetomidine 0.5 μg/kg(initial dose) was given over more than 10 min after anesthesia induction， followed by continuous infusion at 0.4 μg·kg-1·h-1, until the end of operation．The equal volume of normal saline was given instead of dexmedetomidine in group C．Before administration(T0)，30min after begainning of CPB, at 30min, 4 and 24 h after termination of CPB(T1-4)，blood samples were collected for determination of NF-κB activity , apoptosis rate and express of  caspase-3 of polymorphonuclear neutrophils. 
Results  Compared with the baseline value at T0, NF-κB activity of polymorphonuclear neutrophils was significantly increased, the value  of group D was decreased than that of group C at T1-4, there were statistically significantly difference between groups, time points and their interaction（P＜0.05）. Apoptosis rate and express of  caspase-3 of polymorphonuclear neutrophils were gradually decreased at T0-T2, and then increased at T3, T4, while significantly decreased than that of T0 in two groups, and the value  of group D was increased than that of group C at T1-4, there were statistically significantly difference between groups and time points（P＜0.05）. The apoptosis rate of polymorphonuclear neutrophils was negatively correlated with the activity of NF-κB（group C：r=-0.606， P＜0.05；group D：r=-0.691， P＜0.05）.  
Conclusion  The inhibition of NF-κB activity is involved in the reduction of apoptosis inhibition of polymorphonuclear neutrophils in peripheral blood in pediatric patients undergoing open heartsurgery under cardiopulmonary bypass by dexmedetomidine .

Key words: extracorporeal circulation, NF-kappa B, child