Stable isotopic quantitation of protein metabolism and energy expenditure in neonates on- and post-extracorporeal life support

It is generally assumed that extracorporeal life support (ECLS) provides a metabolic 'rest state' by replacing approximately 80% of cardiopulmonary work. The aim of this study was to precisely quantify neonatal energy expenditure (EE) and whole-body protein metabolism on (during) and post (after) venoarterial ECLS using stable isotope tracer techniques. Nine parenterally fed neonates on-ECLS were studied at 7.8 ± 1.0 days of life (mean ± SE), five of which were studied post-ECLS on 27.0 ± 5.4 days of life. EE and whole-body protein metabolism were quantified using a primed, continuous infusion of L-[1-¹³C]leucine and NaH¹³CO₃. The neonates studied on- and post-ECLS had similar rates of endogenous leucine flux (370 ± 46 μmol/kg/h v 339 ± 76 μmol/kg/h), leucine oxidation (161 ± 22 μmol/kg/h v 121 ± 25 μmol/kg/h), nonoxidative disposal rates of leucine (313 ± 37 μmol/kg/h v 331 ± 75 μmol/kg/h), net protein balance (-2.31 ± 0.8 g/kg/d v -0.33 ± 1.1 g/kg/d), and EE (88.6 ± 7.7 kcal/kg/d v 84.3 ± 9.2 kcal/kg/d). These results demonstrate that neonates on-ECLS are in hypermetabolic and protein catabolic states that continue in the post-ECLS phase. The authors conclude that ECLS does not provide a metabolic 'rest state'.