The effect of vascular access modality on changes in fluid content in the arms as determined by multifrequency bioimpedance

Introduction. Intradialytic hypotension remains the commonest complication of routine outpatient haemodialysis treatments. Multifrequency bioimpedance allows assessment of body fluid volumes. Multifrequency bioimpedance can potentially monitor changes in extracellular volume during dialysis and may therefore help to reduce intradialytic hypotension. Hypotension-prone patients have been reported to start dialysis with relatively more fluid distributed in the trunk than the arms. However, as arterio-venous fistulae are the preferred form of vascular access and fistulae could potentially affect fluid retention in the arm, we investigated whether multifrequency bioimpedance could detect differences in fluid distribution in the arms with haemodialysis in patients with different vascular access modalities. Methods. We audited the change in extracellular water (ECW) and total body water (TBW) in the arms following haemodialysis in 100 patients attending for routine outpatient haemodialysis at a university centre by multifrequency bioimpedance using an eight-electrode contact technique. Results. Patients with fistulae had greater ECW/TBW % in the fistula arm both prior to and post dialysis compared with central venous catheter (CVC) (pre 38.9 +/- 0.1 vs 38.3 +/- 0.1 and post 38.4 +/- 0.1 vs 37.8 +/- 0.1, P < 0.01), with a greater absolute difference between arms (0.53 +/- 0.01 vs 0.05 +/- 0.01, P < 0.01) and greater arm ECW/TBW % compared with total body ECW/TBW% predialysis (forearm fistula 99.4 +/- 0.4 vs CVC 97.2 +/- 0.3, P < 0.01). Conclusion. Absolute and also relative extracellular fluid volumes are increased in the fistula arm of haemodialysis patients. Thus, if algorithms are to be developed to monitor relative segmental changes in extracellular volumes to help prevent intradialytic hypotension using bioimpedance, then the dialysis vascular access and site will have to be considered, particularly if using relative changes in the upper limbs. Thus, alterative sites which are not so affected by vascular access, such as the calf, may prove advantageous.