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Effect of access recirculation on the modeled urea distribution volume
J T Daugirdas1, D Schneditz, D J Leehey
1Department of Medicine, University of Illinois, Chicago, IL, USA.
Summary
Vascular access recirculation (AR) can inaccurately affect the modeled urea distribution volume (V). Proper blood sampling is crucial; otherwise, AR may cause V to decrease or remain unchanged, depending on the urea reduction ratio (URR).
Area of Science:
- Nephrology
- Biomedical Engineering
- Mathematical Modeling
Background:
- Vascular access recirculation (AR) is a common complication in hemodialysis.
- Accurate assessment of urea distribution volume (V) is essential for effective dialysis prescription.
- The impact of AR on V estimation can be complex and depends on sampling methods and AR timing.
Observation:
- When blood samples are properly collected, AR present throughout dialysis can lead to an unexplained increase in modeled V.
- Sampling from the arterial line after pump cessation can result in postdialysis blood urea nitrogen (BUN) not reflecting true patient BUN.
- Under these sampling conditions, AR often causes an unexplained decrease in modeled V, though V may remain unchanged based on the urea reduction ratio (URR).
Findings:
- Mathematical analysis predicts that uniformly present AR leads to underestimated V when URR is ≤0.70.
- When URR is >0.70, significant AR may not alter the modeled V.
- AR limited to the end of dialysis or increasing AR, combined with admixed postdialysis BUN samples, almost always leads to V underestimation.
Implications:
- The study highlights the critical importance of proper blood sampling techniques to avoid misinterpreting V during hemodialysis.
- Findings suggest that underestimation of V due to AR may occur frequently, potentially impacting dialysis adequacy assessments.
- Further research may be needed to refine V modeling techniques that account for various AR scenarios and sampling methods.