Acute Effects of Hypoxic Gas Admixtures on Pulmonary Blood Flow and Regional Oxygenation in Children Awaiting Norwood Palliation

Introduction Oxygen delivery in patients with functionally univentricular hearts awaiting Norwood palliation depends on a balance between systemic blood flow (Qs) and pulmonary blood flow (Qp). Modulations of pulmonary vascular resistance and systemic vascular resistance are utilized to maintain balanced Qp:Qs in a circulation prone to pulmonary overcirculation at the expense of systemic perfusion. This study aimed to characterize changes in Qp:Qs and regional (cerebral and renal) oxygen delivery in patients awaiting Norwood palliation receiving hypoxic gas admixture therapy. Methods Patients who received care prior to Norwood palliation were identified from 2014 to 2018. Of these patients, those with cerebral and renal near-infrared spectroscopy were identified (NIRS). Arterial oxygen saturation by pulse oximetry, renal NIRS, and cerebral NIRS prior to hypoxic gas admixture initiation were compared to values six hours, 12 hours, and 24 hours after initiation. Results A total of 28 patients were eligible for inclusion in the study. Arterial saturation by pulse oximetry was 91% prior to initiation and decreased to 86% 24 hours after initiation (p<0.001). Cerebral NIRS were a mean of 60 prior to initiation compared to 58 at 24 hours (p=0.187). Renal NIRS were a mean of 60 prior to initiation compared to 57 at 24 hours (p=0.120). Calculated Qp:Qs was 9.6 at baseline compared to 2.5 at 24 hours (p=0.006). Arteriovenous difference and lactate did not significantly change with hypoxic gas admixture administration. Conclusion Administration of hypoxic gas admixture to patients with functionally univentricular hearts awaiting Norwood palliation decreases the ratio of Qp and Qs but does not improve regional oxygenation delivery.