A novel bioimpedance technique to monitor fluid volume state during hemodialysis treatment.

Bioimpedance spectroscopy is a potential candidate for monitoring of body fluids during dialysis. In this article, the suitability of knee-to-knee (KK) as an alternative to wrist-to-ankle (WA) bioimpedance spectroscopy measurements during dialysis is evaluated. Measurements on eight patients (22 dialysis sessions) showed a good correlation between the change in extracellular resistance (Re) in KK and WA measurements. A deeper analysis indicated that the change in Re normalized for ultrafiltrated volume [DeltaRe/UFV (%/L)] depends on the characteristics of the patient: clinically stable patients [with a presumed lower extracellular fluid - total body volume (VB) relationship] show a higher DeltaRe/UFV (%/L) mean +/- standard deviation (WA: 8.90 +/- 1.9 and KK: 8.29 +/- 2.2) than clinically unstable patients with pitting peripheral edema (WA: 2.10 +/- 0.8 and KK: 2.07 +/- 0.2). Simulations based on bioimpedance equations considering Hanai theory confirm the results. The KK method, especially in combination with proper use of the introduced DeltaRe/UFV (%/L) normalization could possibly offer new options for comfortable online monitoring and the evaluation of fluid volume state during dialysis.