Evaluating calf bioimpedance measurements for fluid overload management in a controlled environment.

Objective: To evaluate the relationship between calf bioimpedance measurements and fluid removal in a controlled environment (hemodialysis) as a first step toward using these measurements for remote congestive heart failure (CHF) monitoring. Approach: Calf bioimpedance measurements were recorded in 17 patients undergoing hemodialysis (9/17 (53%) CHF, 5/17 (30%) female). Measurements were performed before and after hemodialysis. Additional parameters related to hemodialysis and patient fluid status such as estimated dry weight were also recorded. Main results: Calf bioimpedance changes depended on calf fluid status as assessed by calf normalized resistivity (CNR). Patients with lower calf fluid overload (as assessed by CNR greater than 0.1017 Omega m(3) kg(-1)) had larger decreases in calf fluid than patients with higher calf fluid overload. High CNR patients had fluid changes within the calf that depended on the ultrafiltration rate, with patients with lower ultrafiltration rates experiencing fluid shifts from extracellular to intracellular fluid. Additionally, there were correlations between changes in calf extra-, intra- and total- water and the ultrafiltration volume removed for high CNR patients (R-2 = 0.44, 0.42, 0.56, respectively, all p-values < 0.05). Significance: These results suggest that while the relationship between calf fluid status and total fluid status is complex, changes in calf volumes comparable to those expected in an ambulatory setting are measurable and relate to changes in total volume. This suggests that calf bioimpedance measurements for CHF remote monitoring warrant future investigation, as remote fluid status management could reduce fluid overload related hospitalizations in CHF patients.