Optimal current frequency for the detection of changes in extracellular water in patients on hemodialysis by measurement of total body electrical resistance.

Abstract

Measurement of total body electrical resistance (TBER) to an alternating current is useful to monitor extracellular water (ECW) in patients on hemodialysis (HD). Which current frequency is preferable is subject of ongoing debate. The aim of this study was to quantify the implications of TBER measurements at current frequencies ranging from 0 to 1000kHz for ECW monitoring in patients on HD. Bioimpedance spectroscopy measurements were performed in 39 patients on HD using the Body Composition Monitor (BCM, Fresenius Medical Care). TBER data at 5, 50, 200, 500, and 1000kHz were compared with the extrapolated TBER at 0kHz (TBER0) assessed by Cole-Cole analysis. Sensitivity of each TBER configuration was evaluated at individual level, by assessment of the smallest ultrafiltration (UF) volume that induced a significant change in TBER, i.e. a change in TBER≥2.7%. TBER precision was very high for all frequencies, with coefficients of variation of 0.25%-0.28%. Baseline TBER decreased with increasing current frequency. TBER was 2.9% lower at 5kHz(P<0.001), 11.6% lower at 50kHz, and up to 22.0% lower at 1000kHz. This pattern is attributed to a progressive increase in intracellular current conduction at higher frequencies. Sensitivity to volume changes induced by UF also decreased with increasing current frequency. At 0 and 5kHz, an UF volume≤0.5L was sufficient to induce a significant increase in TBER in 87% of patients. This decreased to 69% at higher frequencies. ECW monitoring by TBER requires measurement at 5kHz or less to ensure optimal performance.