Effective ionic dialysance/blood flow rate ratio: An indicator of access recirculation in arteriovenous fistulae

Effective ionic dialysance (EID) is an online measure of hemodialysis (HD) effective urea clearance that is calculated using changes in dialysate sodium conductivity. Effective ionic dialysance is blood flow (Qb) dependent. The presence of significant (≤5%) access recirculation (sAR) during dialysis lowers EID at a given Qb, thereby lowering EID/Qb. We propose using EID/Qb as a useful chairside tool for detection of sAR in arteriovenous fistulae (AVF). Data were collected from 47 patients with AVF (72% men, mean age 49 ± 11.8 years, duration on dialysis 3.78 ± 3.4 years, duration of fistula use 3.35 ± 3.42 years) dialyzed with an high-efficiency dialyzer with a mass transfer area coefficient (KoA) of 1714 ml/min. Effective ionic dialysance were measured at regular intervals by the Gambro Phoenix dialysis system during treatments. The access recirculation (AR) and access blood flow (Qa) were measured using the reference standard saline dilution technique (Transonic HD-02 monitor). Among the 323 HD sessions where Qb, EID, AR, and Qa were available, we identified 17 instances of sAR. The performance of EID/Qb as indicator of sAR was assessed by a receiver operator characteristic (ROC) curve (Stata version 10.1). The area under the ROC curve was 0.935 (95% confidence interval 0.869-1.000), which demonstrated a sensitivity of 76.5% and specificity of 96.4% at an EID/Qb ≤50% with a positive likelihood ratio of 21, negative likelihood ratio of 0.24, positive predictive value of 54.2%, and negative predictive value of 98.7%. We found similar test performance in patients who received HD with dialyzers with smaller surface areas and lower KoAs. The high specificity of EID/Qb makes it an excellent yet simple and early chairside indicator of AVF recirculation.