Bioimpedance analysis of fluid compartments in female CAPD patients

Dry weight is difficult to determine in continuous ambulatory peritoneal dialysis (CAPD) patients. Bioimpedance spectroscopy using a multi-frequency analyzer was used to measure total body water, extracellular water, and intracellular water in 7 female CAPD patients and, for comparison, in 6 normal female controls. One patient was measured a second time after a 10-kg fluid loss. Mean weight in controls and CAPD patients was similar, as was the percent of body weight that was water. However, the ratio of extracellular water to intracellular water was 0.814 in controls but 1.11 in CAPD patients, suggesting either more extracellular water and/or less intracellular water in the CAPD patients compared to the controls. When analyzed, the percent of total body water that was extracellular was significantly greater in the CAPD group. There was also a significant reduction in the percent of intracellular water that contributed to body weight in the CAPD patients. Body cell mass was 38.1% in controls but only 30.2% in CAPD patients. Serum albumin concentration ranged from 2.1 to 4.2 g/dL in CAPD and a linear relationship was present between serum albumin concentration and cell membrane capacitance. We conclude that 60% of body weight as body water may be an overestimate of volume (V) when the formula Kt/V is used to measure adequacy, and that bioimpedance spectroscopy may be a useful technique for assessing both fluid balance and body cell mass or nutritional status in CAPD patients.