Relationship Between Pulmonary-to-Systemic-Blood-Flow Ratio (Qp:Qs) Based on Cardiac Catheterization and Indices...

CO2 removal by the lungs depends upon ventilation and pulmonary blood flow, with end tidal CO2 (EtCO2) as surrogate for it. We studied indices based on EtCO2 measured routinely during anesthesia for cardiac catheterization, along with simultaneously calculated Qp:Qs (pulmonary-to-systemic-blood-flow ratio) in children with complex congenital heart disease to assess the relationship between these measures. A retrospective, single-center, correlational cohort study was conducted at a tertiary-care, free-standing children's hospital. All included subjects had Qp:Qs calculated as well as EtCO2 and PaCO2 documented during a single cardiac catheterization. Children with stage-1 single ventricle or complex biventricular repair with highly variable Qp:Qs were defined as Group 1, and Group 2 comprised those with stage 2 or 3 repairs with less variable Qp:Qs. Exclusion criteria were uncuffed artificial airway, EtCO2 > PaCO2, and abnormally high Qp:Qs. EtCO2 indices were defined as EtCO2:PaCO2 (alveolar functional fraction) and EtCO2 gap (PaCO2-EtCO2). Correlation coefficients were obtained between Qp:Qs and EtCO2 indices in both groups. A total of 29 patients in Group 1 and 24 in Group 2 underwent final analysis. Even with highly variable Qp:Qs, Group 1 showed a strong correlation between Qp:Qs and EtCO2:PaCO2 (r = 0.83, p < 0.0001). A similarly strong correlation was maintained in Group 2 (r = 0.79, p < 0.0001) and in both groups combined (r = 0.86, p < 0.0001). A very strong negative correlation was present between Qp:Qs and EtCO2 gap (r = - 0.77, p < 0.0001). EtCO2:PaCO2 has a very strong correlation with Qp:Qs simultaneously calculated during catheterization. It can be an additional parameter to estimate Qp:Qs in critical management of children with congenital heart disease. Our results also provide a basis for future prospective studies to assess dynamic changes in EtCO2-based indices and Qp:Qs.