Vascular refilling in hemodialysis using feedback-controlled ultrafiltration profile

Background: The rate and the duration of ultrafiltration (UF) are considered the most important factors to affect vascular refilling. The aim of the study was to investigate whether a UF profile could improve the vascular refilling. Methods: Dialysis was delivered by a machine providing feedback control of ultrafiltration rates. Absolute blood volume (BV) was measured by dialysate bolus method. Vascular refilling volume (Vref) was calculated as UF volume – Δ absolute BV. Results: In 40 patients, refilling fraction (Vref/UF volume) was 30.5% in the first hour. Thereafter, refilling fraction steeply increased and reached maximum values in the third and fourth hour at about 95%. The cumulative refilling fraction was 68.5 ± 9.4% at the end. In 14 patients, refilling data from the feedback-controlled UF profile were compared to dialysis sessions with constant UF rates. In 12 of 14 patients, refilling fraction was significantly (p = 0.013) higher in sessions with UF profile (71.6% vs 64.4%). There was a significant negative correlation (r = -0.606; p = 0.002) between the blood volume to extracellular volume ratio and the refilling fraction. The sum of this ratio and the refilling fraction was 1.01 ± 0.06. Conclusions: Despite significant differences, a feedback-controlled UF profile has no advantage over the previous refilling studies with regard to the refilling fraction because vascular refilling seems to depend mainly on the ratio of BV to ECV. This would explain the different results in studies using BV guided UF feedback programs.