TOTAL-BODY WATER AND BODY-COMPOSITION IN CHRONIC PERITONEAL-DIALYSIS PATIENTS

In this investigation, total body water (TBW) in ten chronic peritonea l dialysis patients was studied by deuterium (TBW-H-2), skinfold thick ness (TBW-ST), Watson formula (TBW-WA), 58% of body weight (TBW-58%), and bioelectrical impedance (TBW-BIA), and these results were compared with the reference oxygen(18) (TBW-O-18) method. We also analyzed the fat-free mass (FFM) by skinfold thickness (FFM-ST), bioelectrical imp edance (FFM-BIA), oxygen(18) (FFM-O-18), and creatinine kinetics metho d (FFM-CK). In addition, resting metabolic rate was measured by indire ct calorimetry. Compared with TBW-O-18, TBW-58% and TBW-BIA were signi ficantly different (P < 0.01). TBW-H-2 overestimated TBW-O-18 by 4.3%. TBW-ST and TBW-WA gave slightly greater values than TBW-O-18, althoug h these values were nonstatistically significant. The best prediction of total body water from these methods was obtained with the Watson fo rmula. When Kt/V was calculated from these results, the values obtaine d were statistically greater (BIA, P < 0.001) and smaller (58% BW, P < 0.01) than those obtained with either O-18 Or Watson formula. The fat -free mass estimation also led to discrepant findings. Indeed, FFM-CK was significantly lower (P < 0.05) as compared with FFM-ST, FFM-BIA, o r FFM-O-18. Resting metabolic rate was strongly correlated with FFM es timated by skinfold thickness (r = 0.91, P < 0.001), bioelectrical imp edance (r = 0.85, P < 0.005), and O-18 (r = 0.77, P < 0.01), but not w hen fat-free mass was estimated by the creatinine kinetic method. The water content of fat-free mass estimated by skinfold thickness was fou nd to be 69.7 +/- 6.9% in these patients, a value lower than the stand ard 73.2% found in healthy adults. This study confirms that there is a n abnormal water distribution in chronic peritoneal dialysis patients. However, when compared with the oxygen(18) reference method, the Wats on formula allows a reliable estimation of Kt/V.