Simplified approach to calculation of V, G, and nPCR for monitoring hemodialysis patients.

Abstract

Urea kinetic modeling (KM) permits the calculation of urea volume (VKM), urea generation rate (GKM), and normalized protein catabolic rate (nPCRKM) but requires complex, iterative calculations. Simpler methods for estimation of these parameters (V(est), G(est), nPCR(est)) were compared with those obtained from kinetic modeling. Kinetic modeling was performed on 17 patients using the 3 BUN method, producing 19 data sets. All were within 25% ideal body weight and all had less than 20% difference between VKM and V(est). V(est) was estimated as 0.195 (height) + 0.296 (weight) - 14.01. G(est) was estimated, using interdialytic changes as: [formula: see text] where U is urinary urea excretion rate. nPCR(est) was estimated as: (G(est) x 9.35) + (0.294 x V(est)) x (0.58/V(est)). There was no significant difference (Student's t test) between mean +/- SD V(est) (41.24 +/- 3.86 L) and VKM (40.71 +/- 5.24 L), G(est) (7.23 +/- 1.92 mg/min) and GKM (7.04 +/- 2.10 mg/min), and nPCR(est) (1.12 +/- 0.24 g/kg/day) and nPCRKM (1.10 +/- 0.23 g/kg/day). Correlation between V(est) and VKM was poor (r2 = 0.56, slope = 0.41). Correlations between G(est) and GKM and nPCR(est) and nPCRKM were good (r2 = 0.95, slope = 0.87; and r2 = 0.99, slope = 1.02, respectively). Assessment of nutritional status using G(est) and nPCR(est) can be carried out with high degree of accuracy even if V(est) and VKM are not identical.