Vascular refilling is independent of volume overload in hemodialysis with moderate ultrafiltration requirements.

Introduction Blood volume changes and vascular refilling during hemodialysis (HD) and ultrafiltration (UF) have been assumed to depend on volume overload (Vo ). It was the aim to study the magnitude of vascular refilling in stable HD patients with moderate volume expansion in everyday dialysis using novel technical approaches. Methods Patients were studied during routine dialysis and UF based on clinical dry weight assessment. Pre-dialysis Vo was independently measured by bioimpedance spectroscopy. Vascular refilling volume (Vref ) was calculated as: Vref  = Vuf  - ΔV, where ΔV is the absolute blood volume change determined by on-line dialysate dilution using a commercial on-line hemodiafiltration machine incorporating a relative blood volume monitor, and where Vuf is the prescribed UF volume. Findings Thirty patients (dry weight: 81.0 ± 17.8 kg) were studied. Pre-dialysis Vo was 2.46 ± 1.45 L. Vuf was 2.27 ± 0.71 L, specific UF rate was 6.45 ± 2.43 mL/kg/h, and since ΔV was 0.66 ± 0.31 L, Vref was determined as 1.61 ± 0.58 L, corresponding to a constant refilling fraction (Fref ) of 70.6 ± 10.6%. Vref strongly correlated with Vuf (r(2)  = 0.82) but was independent of Vo and other volumes. Fref was also independent of Vo and other volumes normalized for various measures of body size. Discussion While vascular refilling and Fref is independent of Vo in treatments with moderate UF requirements, intravascular volume depletion increases with increasing UF requirements. The relationship between blood volume and Vo needs to be more closely examined in further studies to optimize volume control in everyday dialysis.