Background: Extensive neonatal resuscitation with chest compressions leads to hypoxic injury as evidenced by encephalopathy, myocardial dysfunction, leading to morbidity and mortality. Although the blood flow to vital organs is pressure passive during the post-resuscitation phase following asphyxia, studies have shown that fluctuations in carbon dioxide could influence cerebral and myocardial perfusion and oxygenation. In a neonatal model of asphyxia with an open ductus, there are no studies evaluating the role of carbon dioxide fluctuations on cerebral, myocardial, pulmonary, and ductal hemodynamics and oxygenation.
Objective: To study the effect of arterial carbon dioxide (PaCO2) levels, (hypocapnia - <35 mmHg, normocapnia 35 – 50 mmHg, hypercapnia >50 mmHg) during the immediate post-resuscitation phase following extensive resuscitation on hemodynamics and oxygenation.
Methods: Blood gas and hemodynamic parameters (coronary blood flow (CoBF), carotid flow (CBF), pulmonary flow (PBF), ductal flow (DBF), mean blood pressure (MBP)) were obtained 30 min post-resuscitation from 7 term lambs (138 – 141 days). The oxygen delivery to the brain and heart were calculated using blood gas parameters and blood flows. Correlation, parametric, and non-parametric analyses were performed.
Results: Eighty-four time points between 30 & 150 min were analyzed. With stable MBP (~40 mmHg), there was a significant positive correlation between PaCO2, CoBF (R-0.59), and CBF (R-0.64) as shown in fig 1A & 1B. The CoBF and CBF was significantly different with hypo, normo & hypercapnia (fig 1A & 1B). Along with changes in PaCO2, the pH and DBF were significantly different between hypo and hypercapnia (table 1). Although there was no statistically significant difference in arterial oxygenation (PaO2) and PBF (table 1), the oxygen delivery to the myocardium and brain was significantly affected by fluctuations in PaCO2 (fig 1C & fig 1D).
Conclusion: In the immediate post-resuscitation phase, avoiding hypocapnia is important to maintain perfusion, and oxygenation of the brain and heart. These findings confirm the higher risk of increased death/disability at 2y with hypocapnia in the post-resuscitation period (Pappas et al. 2011). With an open ductus, PBF and oxygenation are maintained with normocapnia. It remains unknown if higher flows and oxygenation associated with hypercapnia are beneficial/harmful given the risk of reperfusion injury in the immediate post-resuscitation phase.
