Abstract: Objective To investigate the clinical significance and correlation of end-tidalcarbon dioxide partial pressure (PetCO2) and arterial blood carbon dioxide pressure (PaCO2) of children with different types of congenital heart disease in perioperative period of cardiopulmonary bypass.Methods 60 children undergoing selective cardiopulmonary bypass surgery for congenital heart disease were chosen (aged 1-14 years old, ASA class II or III) .According to echocardiographic results, the children were divided into two groups. Group A:Left-to-right shunt in children, involving 15 cases of atrial septal defect and 15 cases of ventricular septal defect;Group B: Right-to-left shunt in children, involving 30 cases of Fallot tetrad. All 60 children underwent intravenous general anesthesia and rapid induction of orotracheal intubation. All patients underwent ventilator-assisted ventilation in the surgical intensive care unit for 8 hours after surgery. The brachial artery blood was collected for arterial blood gas analysis to measure PaCO2 at the beginning of surgery (T1) , 15 min after anesthesia (T2) , before CPB (T3) , 15 min after CPB (T4) , end of surgery (T5) , time to transfer to SICU (T6) , 2 h after monitored in ICU (T7) , 4 h after monitored in SICU (T8) , 6 h after monitored in SICU (T9) , 8 h after monitored in SICU (T10) .The PaCO2 and PetCO2 were recorded at each time point. According to the result of PetCO2 and PaCO2, we studied the correlation of the two indexes at each time point.Results In group A, there was a positive correlation between PetCO2 and PaCO2 at each time point (the correlation was 0.55 to 0.87, P<0.001) . The correlation between PETCO2 and PaCO2 decreased gradually during T2-6, and the correlation gradually increased during T7-10. There was no significant correlation between PetCO2 and PaCO2 (the correlation was0.21 to 0.38, P > 0.05) before operation in group B until 15 minutes after CPB. From the end of surgery to 8 hours after SICU monitoring, PetCO2 was positively correlated with PaCO2 (the correlation was0.54 to 0.83, P < 0.05) .The correlation between the two indexes increased gradually during T5-10. Conclusions During the perioperative period of cardiopulmonary bypass, PetCO2 can be used as an evaluation indicator for clinical monitoring in the children with Left-to-right shunt of congenital heart disease.There was no significant correlation between PetCO2 and PaCO2 in the children with congenital heart disease of right-to-left shunting before the end of surgery. PetCO2 could not replace PaCO2.With the improvement of postoperative conditions, It is significant to dynamically observe changes in PetCO2 to guide the analysis of PaCO2.