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A. Grzegorzewska, Protein catabolic rate (PCR), dietary protein intake (DPI) and metabolic acidosis, Nephrology Dialysis Transplantation, Volume 14, Issue 9, September 1999, Pages 2266–2267, https://doi.org/10.1093/ndt/14.9.2266
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Sir,
I have read with great interest the article by Movilli et al. [1] and a comment of Iorio et al. [2], concerning the relationships between PCR, DPI and metabolic acidosis. With the aim of adding further information on this issue, I would like to present the results of PCR, DPI and blood gas parameters obtained in continuous ambulatory peritoneal dialysis (CAPD) patients.
In our uraemic patients (n=55; Female, 16 and Male, 39; age 45±12 years) treated with CAPD through 1–27 (19±11) months, values of PCR and DPI, daily energy intake (DEI), blood acid–base parameters and nitrogen balance were evaluated every 3 months. PCR was calculated according to Randerson et al. [3] and normalized to total body mass (TBM), ideal body mass (IBM), TBW/0.58 (TBW, total body water) and lean body mass (LBM) estimated according to three methods: (i) from creatinine kinetics using the method of Keshaviah et al. [4]—LBMcr; (ii) from anthropometric measurements—LBManthr; and (iii) from the relationship LBM=TBW/0.73. Values of DPI and DEI were obtained on the basis of diet histories taken by an experienced dietetician and checked against coloured pictures of individual foods and meals for accuracy. DPI and DEI were calculated using the computer program FOOD version 1.0 (The Institute of Nutrition and Food, Poland, licence 017). DPI was normalized as aforementioned for PCR. TBW was estimated according to the method of Watson et al. [5]. Parameters of acid–base balance were obtained from arterialized capillary blood using Blood Gas Analyzer Compact 1 (Austria). Daily nitrogen balance was calculated as the difference between nitrogen intake and nitrogen loss. Nitrogen intake was calculated as DPI/6.25 (g/day). Nitrogen loss was calculated as a sum of total nitrogen removal in dialysate and urine, basing on the nitrogen determinations performed by the modified Kjeldahl method [6]. A fixed amount of 1.824 g was taken into consideration accounting for nitrogen from protein (1.504 g) and amino acids (0.32 g) lost through the gastrointestinal tract and skin daily [7,8]. This fixed amount of nitrogen was also subtracted from values of nitrogen intake. Positive values of nitrogen balance indicate uptake of nitrogen (anabolic processes), negative values of nitrogen balance mean a loss of nitrogen (catabolic processes). Total DEI was calculated as oral DEI taken from diet record analysis plus DEI from glucose absorbed from the peritoneal cavity minus energy from glucose lost with daily urine. Total DEI was normalized to TBM.
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