Evaluation of the correlation between end-tidal arterial carbon dioxide pressure based on mainstream capnography technique and arterial carbon dioxide pressure based on arterial blood gas analysis before and after cardiopulmonary bypass pump in children with non-cyanotic congenital heart defects

Background. It is still a matter of debate whether the evaluation of end-tidal carbon dioxide (ETCO2) using a capnography device allows the evaluation of non-invasive monitoring of arterial carbon dioxide pressure (PaCO2). The aim of this study was to compare the value of ETCO2 by direct mainstream and PaCO2 based on arterial gas analysis (ABG) before and after cardiopulmonary bypass pump in children with congenital heart defects. Methods. Twenty nine children who were candidates for elective cardiac surgery and were admitted to the Children's Medical Center were enrolled. Before and after cardiopulmonary bypass pump, ETCO2 was evaluated based on mainstream technique and PaCO2 based on arterial gas analysis. Results. The mean difference between ETCO2 and PaCO2 values before cardiopulmonary bypass pump was 3/68 ± 5/32 mm Hg, which considering that the difference of less than 5 mm Hg is clinically negligible, indicates an acceptable agreement between them. However, the mean difference between the two indices after cardiopulmonary bypass pump was 7/0 ± 6/85 mm Hg that accordingly, the difference between the two measured values after cardiopulmonary bypass will be clinically significant. Conclusion. Preoperative ETCO2 evaluation can provide a close prediction of PaCO2 levels, but after pumping, direct arterial sampling should be taken to accurately measure PaCO2 levels in non-cyanotic patients undergoing heart surgery. Practical Implications. When confronting with a child with non-cyanotic heart defect undergoing surgery, we suggest relying on capnography as a mirror of arterial blood pressure of carbon dioxide. However, capnography may not be as reliable during early post-bypass period in this group of patients and repeated arterial blood samples may be necessary.