FRACTIONAL UREA CLEARANCE IN CONTINUOUS AMBULATORY PERITONEAL-DIALYSIS - EFFECTS OF VOLUME DISTURBANCES

The effects of volume disturbances on the KT/V were investigated prosp ectively in 133 consecutive urea clearance studies on patients on cont inuous ambulatory peritoneal dialysis (CAPD). Four subjects (group A) had fluid loss (actual weight < dry weight), 57 (group B) were studied on the basis of their dry weight, 58 (group C) had moderate fluid exc ess (0-5% of dry weight), and 14 patients (group D) had severe fluid e xcess (>5% of dry weight). The KT/V was calculated on the basis of dry weight and actual weight with V obtained from the Watson anthropometr ic formulae which were applied either uncorrected or with a correction for changes in body water from dry weight conditions. The groups were compared by variance analysis. The following weekly KT/V estimates we re obtained: (1) using dry weight V: group A 1.81 +/- 0.17, group B 2. 0 +/- 0.59, group C 1.79 +/- 0.46, group D 1.85 +/- 0.37 (no differenc e between groups); (2) using uncorrected actual weight V: group A 1.85 +/- 0.15, group B 2.05 +/- 0.59, group C 1.77 +/- 0.45, group D 1.78 +/- 0.37 (group B had a higher KT/V than group C, p < 0.05), and (3) u sing corrected actual weight V: group A 1.93 +/- 0.14, group B 2.05 +/ - 0.59, group C 1.70 +/- 0.43, group D 1.63 +/- 0.36, (group B had a h igher KT/V than either group C or group D, both at p < 0.01). In CAPD, fluid deficit is rare and causes a small increase in KT/V, whereas fl uid retention is frequent and causes a decrease in KT/V. This decrease is pronounced in patients with severe fluid excess. The uncorrected W atson formulae underestimate V and, consequently, overestimate KT/V in CAPD patients with fluid excess.