Can bio-electrical impedance be used to measure total body water in dialysis patients?
The measurement of total body water (TBW) by bio-electrical impedance (BEI) in a group of renal patients was evaluated against the tritium dilution method. The effect of haemodialysis and the presence of peritoneal dialysate on the impedance were also investigated. The correlation between the two methods was r = 0.9, with the standard deviation of the differences being 3.66 l (TBW typically 40 l). The BEI method overestimated the actual weight loss after haemodialysis, but underestimated the volume of peritoneal dialysate in situ. 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.
