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

Abstract

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.

Vascular Refilling Is Not Reduced in Dialysis Sessions with Morbid Events

“…In that previous study the refilling fraction appeared to be relatively uniform amounting to about 70% of the total UF volume and was independent of the fluid overload [12]. This finding was different from studies where vascular refilling increased especially with severe volume expansion [4,16,17], but it is in line with the refilling fraction of 74 ± 9% identified in nine dialysis patients using a mathematical model [18].…”

“…In a previous study, we found that the refilling volume linearly increased with UF volume in stable chronic HD patients with moderate UF requirements [12]. In that previous study the refilling fraction appeared to be relatively uniform amounting to about 70% of the total UF volume and was independent of the fluid overload [12].…”

“…When the absolute blood volume is known, vascular refilling volume can be calculated from the absolute change in blood volume, and from the known UF volume [12]. Recently, we performed a study on IME-prone patients to identify absolute blood volume at which they developed clinical symptoms [13].…”

Assessing Extracellular Volume in Hemodialysis Patients Using Intradialytic Blood Pressure Slopes

“…It is known that higher ultrafiltration rates/volumes are associated with larger intradialytic decreases in BP [24]. While there is a strong negative correlation between ultrafiltration rate/volume and intravascular blood volume, there is a strong positive correlation between the post-HD volume overload and intravascular blood volume [32]. Importantly, the association between IBPS and ECW/body weight that we found was independent of the ultrafiltration rate.…”

Influence of Hemofiltration on Intradialytic Plasma Volume Decrease

“…In the present study, BW gain and BW/DW in HD were generally larger than in ol-HDF, which might have facilitated the refilling during HD sessions and so underestimated IPVD in HD. However, because fluid excess was reported to not influence refilling [19], the possible difference in fluid excess between the modes would not have significantly influenced IPVD.…”