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.