FC 095INCREASED VASCULAR REFILLING BY FEEDBACK-CONTROLLED ULTRAFILTRATION PROFILE
Authors: Kron Susanne , Leimbach Til , Kron Joachim 
Published: May 2021

Abstract

Background and Aims
Refilling volume has not been a measurable parameter in clinical practice so far, as knowing the absolute blood volume (BV) is a prerequisite. Recently, we developed a method to determine absolute BV, thus enabling quantification and comparison of the refilling volume under various conditions. In this study, we evaluated refilling with a constant UF rate and with a feedback-controlled UF profile.

Method
Forty dialysis patients were included and studied during their routine dialysis sessions. Absolute BV was determined by indicator dilution. Immediately at the beginning of the dialysis session (before UF was started), an on-line infusate bolus of 240 mL was injected into the venous blood line by pressing a button on the keypad of the dialysis machine 5008 (FMC). The resulting increase in relative blood volume before and after bolus administration (RBVpost-RBVpre) was used to calculate absolute BV:
absolute BV (in mL) = bolus volume (240 mL) x 100 / increase in RBV (in %)
Absolute BV at the end of dialysis was calculated as:
absolute BVend = absolute BVbeginning x RBVend in % / 100
Refilling volume was calculated as:
refilling volume = UF volume – (absolute BV beginning – absolute BV end)
The refilling fraction is given as:
Refilling fraction = refilling volume / UF volume
UF was either set as constant UF rate or as UF profile. In contrast to the constant UF rate, the UF program integrated in the dialysis machine 5008 initially starts with twice the average UF rate. If half of the prescribed UF target is reached, the control program keeps UF and refilling in balance.

Results
Refilling data of 40 dialysis sessions with constant UF were compared to 40 sessions with the feedback-controlled UF profile.
Refilling volumes were 1.72 ± 0.76 l during the profiled sessions and 1.60 ± 0.64 l in sessions with constant UF rate (p &lt; 0.001, Wilcoxon test). UF volumes were similar in both treatments (2.20 ± 0.90 and 2.26 ± 0.81 L, respectively).
There was a strong correlation between refilling volume and UF volume in both treatments (r = 0.98 with profile, and r = 0.92 with constant UF rate, respectively).
The refilling fraction was significantly higher (p &lt; 0.001, t-test) with the feedback-controlled UF profile (77.2 ± 8.5%) than with a constant UF rate (70.4 ± 9.9%). In one patient there was a higher refilling fraction with constant UF rate (p &lt; 0.0001).
Symptomatic hypotension occurred in 3 patients, all in sessions with constant UF rate. Refilling was not lower in these 3 cases.

Conclusion
Refilling volume predominantly depended on UF volume. The refilling was improved by a high UF rate at the beginning of dialysis. This confirms previous data that initially high UF rates induce the refilling sooner, and, therefore, the refilling volume is higher with the same UF.
An increased UF rate at the beginning can improve volume management in haemodialysis patients. With a UF profile, more volume can be removed while maintaining a stable absolute BV which may prevent hypotension in some cases. We therefore recommend that such UF profiles should be used more often in routine clinical practice.
However, with every litre of UF volume, BV is reduced by more than 200 ml, at a constant UF rate even by approximately 300 ml. This must be taken into account when prescribing the UF volume.