Kinetic modeling of plasma leucine levels during continuous venovenous extracorporeal removal therapy in neonates with maple syrup urine disease.

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](t) = [Leu](i) x 0.95 x 10(-0.09t) where [Leu](t) is the leucine plasma level (mumol/L) at time t (h) during CECRT and [Leu](I) is the initial plasma level. From h 4 to the end of CECRT, a second exponential curve was observed: [Leu](t) = [Leu](i) x 0.74 x 10(-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 +/- 3% of body weight during the first 3 h of CECRT and 72 +/- 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-molecular-weight solutes such as urea.