What factors contribute to the elevation of serum free fatty acid levels in newborns in the cardiac surgical setting?

Elevations in serum free fatty acid (FFA) levels during heart surgery have been reported in humans and experimental animals, causing increased arrhythmias, decreased heart function, and contributing to mortality. Factors such as heparin administration, age, cardiopulmonary bypass (CPB), and cyanosis or hypoxia have been implicated but not proven. This study was designed to clarify the contribution of these factors using an experimental pig model as follows: (i) adult (n = 10) versus 3-day-old piglets (n = 18) had FFA levels assessed before and after heparin administration; (ii) 3-day-old piglets, the additional effect of CPB (n = 8) or just severe hypoxia (PaO2 = 20-25 mm Hg; n = 6) exposure on FFA levels. This work demonstrated that significant elevations in serum FFA were mainly due to heparin administration, with modest contributions by young age, CPB, and hypoxia. Our preliminary clinical investigations also suggest that children undergoing CPB are at risk of being exposed to high FFA levels and that these patients only suffered a decrease in heart function when these elevations were present in conjunction with cyanosis and (or) prolonged ischemic time. These initial findings require further confirmation. Given these findings, pharmacotherapeutics geared towards limiting FFA elevations should be considered, especially in young children undergoing pediatric cardiac surgery.