Knee-to-knee bioimpedance measurements to monitor changes in extracellular fluid in haemodynamic-unstable patients during dialysis

The feasibility of bioimpedance spectroscopy (BIS) techniques for monitoring intradialytic changes in body fluids is advancing. The aim of this study was to compare the knee-to-knee (kkBIS) with the traditional whole-body (whBIS) with respect to continuous assessment of fluid volume status in hemodialysis patients. Twenty patients divided into two groups, hemodynamically stable and unstable, were recruited. Bioimpedance data from two different electrodes configurations (hand-to-foot and knee-to-knee) were collected and retrospectively analysed. A good correlation between the two methods with respect to changes in extracellular resistance (R_e) and R_e normalized for ultrafiltration volume (ΔR_e/UFV) with p < 0.001 was observed. The relationship between relative change (%) in ΔR_e and that in patient weight was most notable with kkBIS (4.82 ± 3.31 %/kg) in comparison to whBIS (3.69 ± 2.90 %/kg) in unstable patients. Furthermore, results based on kkBIS showed a reduced ability of the thigh compartments to keep up with the volume changes in the trunk for unstable patients. kkBIS provided a comparable sensitivity to whBIS even in patients at risk of intradialytic hypotension while avoiding the need for the complex implementation imposed by whBIS or other configurations.