A kinetic modeling of leucine plasma concentration changes is proposed to describe the plasma leucine reduction rate during continuous extracorporeal removal therapy (CECRT) in neonates with maple syrup urine disease. Data were obtained from seven neonates using a bicompartmental model for the best fitted curve of plasma leucine decrease during CECRT. During the first 3 h, leucine plasma levels decreased according to an exponential curve: [Leu] -0.05t . Plasma leucine levels obtained from three other neonates were similar to those predicted by the model. The apparent distribution volumes for leucine that correspond to the two exponential equations obtained were calculated from the leucine mass removal collected in the spent dialysate and ultrafiltrate. The distribution volume was 34 Ϯ 3% of body weight during the first 3 h of CECRT and 72 Ϯ 7% from h 4 to the end of CECRT. These figures are similar to known values for the extracellular water compartment and for total body water in the newborn. The findings suggest that leucine handling during CECRT is similar to that of nonprotein-bound small-molecularweight solutes such as urea. MSUD is an inherited metabolic disease due to a deficiency in branched chain ketoacid dehydrogenase that leads to the accumulation of BCAA (leucine, isoleucine, and valine) and their keto-acid derivatives (1). Because of this impaired enzyme activity, leucine accumulates in cells and body fluids when the load exceeds leucine metabolism capacity and/or when a increased protein catabolism occurs. Given that renal clearance of BCAA and its derivatives is poor and due to the fact that their acute elevation causes neurologic deterioration, CECRT is indicated in severe cases and/or when nutritional support free of BCAA is not possible (2).Because assessment of leucine plasma levels by amino acid chromatography is not easily available and is time consuming, the aim of this study was to design a kinetic model that predicts leucine plasma level changes over time during the acute phase of the illness in neonates on CECRT.
METHODS
Patients.Between January 1991 and April 2000, seven neonates with MSUD presented with a severe acute deterioration of their status. After a 6-h period of conservative management that included correction of dehydration and increased caloric intake, all seven patients presented two of the three following criteria that are associated with a high risk of severe brain damage: comatose state, gastrointestinal intolerance, and leucine plasma levels Ն1700 M. The patients were referred to pediatric and neonatal intensive care for alternative therapies, in particular CECRT (3). Blood and spent dialysate samples were collected to monitor treatment efficiency. We retrospectively used these biologic analyses to elaborate the parameters involved in leucine kinetic modeling during CECRT (Table 1). Subsequently, between May 2000 and December 2001, three other neonates were treated with the same therapeutic strategy and were retrospectively studied to validate the leucine kinetic model...