The effect of normalization of ECW volume as a marker of hydration in peritoneal dialysis patients and controls.

OBJECTIVES: We measured extraceLlular water (ECW) and intracellular water (ICW) volumes in peritoneal dialysis (PD) patients and controls to determine the effect of ICW variation on ECW/ICW ratio and to compare alternative ratios of ECW to height, height2, weight, and body surface area (BSA). PATIENTS AND METHODS: We measured body water compartments by deuterium oxide and bromide dilution in 29 PD patients (14 M, 15 F) and 31 controls (15 M, 16 F).
RESULTS: ECW was similar in PD patients (17.58 +/- 3.58 L) and controls (17.20 +/- 2.97 L), p = NS. ICW was nonsignificantly lowerin PD patients (17.58 +/- 4.88 L) than in controls (19.71 +/- 5.08 L), p = NS. ECW/ICW was greaterin PD patients (1.06 +/- 0.32) than in controls (0.92 +/- 0.25), p = 0.057, and was inversely correlated with ICW in PD patients (r = -0.733, p < 0.0001) and controls (r = -0.721, p < 0.0001). In contrast, ECW/height, ECW/height2, ECW/weight, and ECW/BSA were similar for the two groups.
CONCLUSIONS: ECW/ICW is affected by changes in ICW as well as by ECW varying with hydration. ECW/ICW ratio leads to the spurious impression of overhydration in subjects with smaller ICW volumes. ECW/ICW does not reflect hydration alone and other methods of expressing ECW as a measure of hydration need further evaluation.