Changes in upper limb extracellular water content 
during hemodialysis measured by multi-frequency bioimpedance

Hemodialysis patients are at risk of chronic volume overload, with consequent increased cardiovascular morbidity and mortality. Multifrequency bioimpedance allows assessment of body fluid volumes. Devices vary from two paired electrodes which measure bioimpedance down one side of the body to four paired electrodes which measure both sides of the body. As arteriovenous fistulae may cause arm swelling, we investigated whether the presence of a fistula affected bioimpedance limb measurements.

We audited the change in extracellular water (ECW) and total body water (TBW) in the arms following hemodialysis in 414 adult patients attending for routine mid-week hemodialysis session 
by multifrequency bioimpedance using a four-paired electrode bioimpedance device (InBody 720; Biospace, Seoul, South Korea).

Patients with right-sided brachial fistulae had a greater percentage ECW/TBW in the fistula arm both prior to and post dialysis compared to those dialyzing with catheters (pre 39.6 ± 3.5 vs. 38.4.3 ± 1.6 and post 38.5 ± 1.3 vs. 37.8 ± 1.1, p<0.01), but there was no difference in the ECW/TBW in the non-fistula arm, pre dialysis between those dialyzing with fistulae compared to catheters, but the ECW/TBW was greater post dialysis with both brachial (38.4 ± 1.1) and radial fistulae (38.1 ± 1.3) compared to those with catheters (37.7 ± 0.9, p<0.05 respectively).

Although absolute and also relative extracellular fluid volumes are increased in the fistula arm of hemodialysis patients, particularly right-sided and with brachial fistulae, the amount of fluid is unlikely to be of clinical significance when making bioimpedance measurements in the non-fistula side of the body to determine volume status.