Nitrogen balance during extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) has been used as a support system for neonates with pulmonary failure since 1975. During ECMO, thermal regulation, pulmonary gas exchange, and cardiac output can be partially or nearly completely provided by the circuit. The presumed resultant decrease in energy requirement has prompted the question of whether infants are in a catabolic or anabolic state of metabolism while on ECMO. Directly measuring the metabolic rate in babies on ECMO is difficult. However, studying the nitrogen balance in these infants may suggest an answer. Nitrogen balance was studied in 21 neonates spanning a single ECMO team's experience at two institutions. Children were studied at the Ochsner Clinic from 1986 to 1990 and at the University of Chicago Wyler Children's Hospital from 1990 to the present. The infants received total parenteral nutrition (TPN) as their only nutritional source during the entire ECMO course. During this time, 24-h urine collections were analyzed for urea nitrogen (UUN). The daily nitrogen balance was calculated by subtracting nitrogen output (estimated as the UUN) from nitrogen input (the measured amino acid content of the intravenous feeding). Fecal losses were not included in the nitrogen output since the infants were not enterally fed and rarely had stools while on ECMO. The kilojoules (1 kilocalorie = 4.2 kilojoules) and protein provided by the parenteral nutrition varied. Nitrogen intake exceeded nitrogen output by ECMO day 2 (the initial nitrogen balance determination). Infants receiving as little as 0.4 g/kg protein and 168 kJ/kg daily remained in positive nitrogen balance.