DETERMINATION OF TOTAL-BODY WATER IN UREMIC PATIENTS BY BIOELECTRICAL-IMPEDANCE

The measurement of total body water by bioelectrical impedance in a gr oup of renal patients was evaluated against the tritium dilution metho d. The effect of haemodialysis and the presence of peritoneal dialysat e on the impedance were also investigated. The correlation between the two methods is r=0.90 with a residual standard deviation of 3.7. The standard deviation of the differences between the two methods against the means was 3.66 which means that total body water (TBW) estimated b y the bioelectrical impedance (BEI) method may be 6.181 (X +/- 2 SD) a bove or 8.381 below the (H2O)-H-3 method. The BEI method overestimated the actual weight loss after haemodialysis (3.87 +/- 1.71 versus 2.43 +/- 1.81) but underestimated the volume of peritoneal dialysate in si tu. The BEI method would not be appropriate for use in assessing total body water and monitoring acute volume changes in patients with renal failure who are on strict fluid restriction.