Changes in Arterial to End Tidal CO2 Difference During Repairing Heart Surgery: Cyanotic Versus Acyanotic Congenital Heart Diseases

Background: End-tidal carbon dioxide (EtCO2) can approximate the arterial pressure of carbon dioxide (PaCO2) in children without underlying congenital heart defects. However, EtCO2 may underestimate PaCO2 in these children, especially during repair procedures. The PaCO2 to EtCO2 difference (Δ PaCO2-EtCO2) may be significant in children with congenital heart disease (CHD) and can be notably influenced by surgical procedures. Postoperatively, the Δ PaCO2-EtCO2 might not remain consistent; thus, arterial blood gas (ABG) analysis may need to be repeated regardless of capnography findings. This hypothesis was tested in our study on children with cyanotic and acyanotic heart defects undergoing corrective surgeries. Methods: In this cross-sectional study, hospital records of all children under 12 years of age with ASA II-III and cyanotic or acyanotic heart defects who were candidates for elective angiography were reviewed. EtCO2 was measured by lateral aspiration capnography. Simultaneous measurements of EtCO2 and PaCO2 were collected before and after the intervention. Results: Significant changes were observed in serum HCO3 concentration and the PaO2/FiO2 ratio, both of which significantly decreased after the repair surgery. However, the change in Δ PaCO2-EtCO2 remained insignificant postoperatively. In the cyanotic group, in addition to a significant reduction in serum HCO3 value and an increase in the PaO2/FiO2 ratio after the intervention, we found a significant decrease in Δ PaCO2-EtCO2. Conclusion: Arterial blood gas analysis during repair surgery should be repeated in the cyanotic congenital heart defects group due to the intraoperative variability of Δ PaCO2-EtCO2, but not in the acyanotic heart defects group due to the stability of this difference. Therefore, EtCO2 assessed by capnography can estimate PaCO2 in children with acyanotic heart defects, but not in those with cyanotic heart defects.