Protein and energy intake, nitrogen balance and nitrogen losses in patients treated with continuous ambulatory peritoneal dialysis

Protein and energy intake, nitrogen balance and nitrogen losses in patients treated with continuous ambulatory peritoneal dialysis. The aim of this investigation was to analyze factors which influence the dietary protein intake (DPI), the energy intake and the utilization of ingested protein, and to determine the relationship between various types of nitrogen losses in stable continuous ambulatory peritoneal dialysis (CAPD) patients. We performed 23 nitrogen balance (NB) studies of 6 to 11 days duration in 12 CAPD patients. One study was performed in all patients 3.4 ± 1.2 months after starting CAPD (early studies). The study was then repeated in nine patients after 12.1 ± 2.6 months, and two of these patients were studied again after 16 and 24 months, respectively (late studies). Before each NB study, the dietary intakes prior to the study were assessed in diaries and interviews. During a few days preceding the NB periods and during the NB periods each patient received an individualized diet composed so as to resemble the patients' spontaneously chosen diet regarding DPI and dietary energy intake (DEI). Total nitrogen, protein, urea and creatinine were analyzed in the dialysate and urine collected daily. Total nitrogen was also analyzed in the feces, collected over the whole NB period. Total nitrogen appearance (TNA), non-protein nitrogen appearance (NPNA) and urea nitrogen appearance (UNA) were calculated by correcting total nitrogen output, non-protein nitrogen output, that is, TNA minus the total protein losses (PL) and urea nitrogen output for changes in total body urea nitrogen. Glucose was determined in the collected dialysate and the daily glucose absorption was calculated. DPI varied between 0.62 and 2.09 g/kg/day, DEI between 21 and 42 kcal/kg/day and the peritoneal energy (glucose) intake (PEI) between 4 and 13 kcal/kg/day. DPI (but not DEI) correlated with Kt/Vurea and Kt/VCr and with total and renal clearances for urea and creatinine. NB (not corrected for “unmeasured” nitrogen losses) was positive in most studies, and it correlated with DPI and the total energy intake (TEI) in the early studies, but only with TEI in the late studies. DPI correlated with TNA, NPNA, UNA, non-protein-non-urea nitrogen loss and fecal nitrogen loss. UNA was highly correlated with TNA and NPNA (r = 0.95). We used data from 33 NB studies in CAPD patients (our present data combined with data from the literature) to calculate regression equations describing the relationship between TNA and NPNA, respectively, and UNA. Equations were derived by which the protein equivalent of TNA (PNA), that is, 6.25 TNA, and the protein equivalent of NPNA (PNPNA), that is, 6.25 NPNA, may be calculated from UNA which is directly measured. In stable CAPD patients, who are not strongly catabolic or anabolic, PNA may be used to estimate DPI and PNPNA may be used to estimate the net protein intake (DPI – PL)