Relationship between alveolar functional fraction and clinical outcomes in children during postoperative care after surgery for single-ventricular heart.

Background: Optimization of pulmonary to systemic blood flow (Qp: Qs) is the key to postoperative care of children with a single-ventricular heart. The ratio of end-tidal CO2 to partial pressure of CO2 called alveolar functional fraction (AFF) has shown a strong relationship with Qp: Qs in the catheterization lab in this population (with Qp: Qs of 1 correlating with AFF of 0.7). As there are no studies to understand the relationship between AFF and clinical outcomes in the postoperative care of these children, this study was carried out.

Methodology and results: This retrospective cohort study included 29 postoperative periods of children who underwent surgery for a single-ventricular heart. The average AFF was calculated for each early postoperative period. The primary clinical outcome was time in hours to normalize lactate. Other clinical outcomes included duration of mechanical ventilation, duration of milrinone infusion; presence of acute kidney injury (AKI), seizures and necrotizing enterocolitis (NEC); need for tracheostomy, need for extra-corporeal support, and mortality in the first 60 days postoperatively. The study population was divided into Group 1 with AFF ≤0.7 and Group 2 with AFF >0.7, to compare the outcome differences between the groups. Time to normalize the lactate had a modest negative correlation with the AFF, with Pearson's r = -0.49 (P = 0.007) for the entire cohort. The clinical outcomes were not statistically different for groups with AFF ≤0.7 and with AFF >0.7, although the group with AFF ≤0.7 had a higher incidence of NEC and higher mortality, whereas the group with AFF >0.7 had a higher incidence of AKI.

Conclusions: In this small study, the AFF showed a modest negative correlation with the time to normalize lactate in postoperative care after surgery for a single-ventricle heart. There were the trends with some other important clinical outcomes but not statistically significant. A larger, multi-center study is needed to delineate these relationships further.