Abstract
Material: Restoration of body water compartments to normal by ultrafiltration is a major goal of hemodialysis. Dry weight is the term used to define normal body water in dialysis patients, but it is limited, as it is based solely on clinical observations. Bioimpedance spectroscopy can accurately measure the resistance of body fluid compartments. The ratio of the resistances of the intracellular to extracellular water should reflect the relative volume of these compartments. As dialysis patients accumulate excess fluid in their extracellular compartment, this ratio may prove useful in the evaluation of dry weight. Methods: We measured the resistances of the intracellular and extracellular fluid compartments in normal subjects to define the normal ratio of the resistances of these compartments. Women had a slightly higher ratio than men (women: 2.41 ± 0.23 vs. men: 2.08 ± 0.23 vs. p < 0.0001). The ratios determined in the normal population were taken as the normal physiologic ratio and were used to define physiologic dry weight. We then compared dialysis patients both pre- and post-dialysis to this normal population. Results: We found that most patients (67%, n = 18) had an elevated ratio pre-dialysis suggesting excess extracellular fluid. Of the 38 treatments in which patients achieved their clinical dry weight, 19 (50%) had persistently elevated R(i)/R(e) ratios, suggesting they had not reached physiologic dry weight. Conclusion: These data suggest that many dialysis patients carry excess extracellular fluid post dialysis despite achieving their clinical dry weight. Furthermore, the resistance ratio derived from bioimpedance spectroscopy may be a useful clinical tool in determining dry weight.