Normalization of protein equivalent of nitrogen appearance and dialytic adequacy in CAPD

Caloric-proteic malnutrition is frequently encountered in peritoneal dialysis and is associated with an increased risk of morbidity and mortality. Our paper aims to assess any greater reliability of protein equivalent of nitrogen appearance (PNA) normalization to desirable body weight (dBW) compared to actual body weight (aBW) and resulting implications for the relationship between dialytic adequacy and protein intake in continuous ambulatory peritoneal dialysis (CAPD). We studied 36 patients on CAPD, 24 male and 12 female (aged 66.6 +/- 10.2 years, 24 +/- 29 months on dialysis), collecting dialysate and urine over 24 hours (126 samples) to calculate the PNA according to Randerson and the total weekly KT/V. The total body muscle mass (TBMM) was calculated by anthropometry and the dBW according to Metropolitan Life Insurance tables. Finally, PNA was normalized to aBW (aPNA, g/kg/day) and to dBW (dPNA, g/kg/day). Average aBW proved to be higher than dBW (66.0 +/- 11.1 vs 59.8 +/- 6.9 kg, p < 0.0001) and aPNA lower than dPNA (0.96 +/- 0.31 vs 1.08 +/- 0.3 g/kg/day, p < 0.005). Compared to aPNA, dPNA correlates better with both blood urea nitrogen (BUN) (R2 = 0.702 vs 0.614) and KT/V (R2 = 0.348 vs 0.306). The TBMM is higher in the group with dPNA > or = 1.0 vs < 1.0 g/kg/day (25.5 +/- 0.6 vs 23.1 +/- 0.7 kg, p < 0.02) while, paradoxically, it is lower in patients with aPNA > or = 1.0 vs < 1.0 g/kg/day (22.8 +/- 0.8 vs 25.4 +/- 0.6 kg, p < 0.01). The KT/V of the patients with dPNA < 0.8, 0.8-1.2 and > 1.2 g/kg/day proved to be different (1.52 +/- 0.06 vs 1.80 +/- 0.03 vs 2.04 +/- 0.04, p < 0.005). On analysis of the linear regression, dPNA = 1.0 and 1.2 g/kg/day corresponds to KT/V values of 1.7 and 2.05, respectively. We consider dPNA to be more suitable then aPNA for the correct assessment of protein intake, and a weekly KT/V of 1.7-2.05 as being sufficient to guarantee satisfactory dPNA.