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 (V-o). 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 V-o was independently measured by bioimpedance spectroscopy. Vascular refilling volume (V-ref) was calculated as: V-ref=V-uf-V, where V 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 V-uf is the prescribed UF volume. Findings Thirty patients (dry weight: 81.0 +/- 17.8 kg) were studied. Pre-dialysis V-o was 2.46 +/- 1.45 L. V-uf was 2.27 +/- 0.71 L, specific UF rate was 6.45 +/- 2.43 mL/kg/h, and since V was 0.66 +/- 0.31 L, V-ref was determined as 1.61 +/- 0.58 L, corresponding to a constant refilling fraction (F-ref) of 70.6 +/- 10.6%. V-ref strongly correlated with V-uf (r(2)=0.82) but was independent of V-o and other volumes. F-ref was also independent of V-o and other volumes normalized for various measures of body size. Discussion While vascular refilling and F-ref is independent of V-o in treatments with moderate UF requirements, intravascular volume depletion increases with increasing UF requirements. The relationship between blood volume and V-o needs to be more closely examined in further studies to optimize volume control in everyday dialysis.