Evaluation of partial pressure CO 2 change in the dialyzer blood inlet during hemodialysis as a measure of vascular access recirculation.

Introduction: Vascular access recirculation during hemodialysis is associated with reduced effectiveness and worse survival outcomes. To evaluate recirculation, an increase in pCO ₂ in the blood of the arterial line during hemodialysis (threshold of 4.5 mmHg) was proposed. The blood returning from the dialyzer in the venous line has significantly higher pCO ₂ , so in the presence of recirculation, pCO2 in the arterial blood line may increase (ΔpCO ₂ ) during hemodialysis sessions. The aim of our study was to evaluate ΔpCO ₂ as a diagnostic tool for vascular access recirculation in chronic hemodialysis patients.
Methods: We evaluated vascular access recirculation with ΔpCO ₂ and compared it with the results of a urea recirculation test, which is the gold standard. ΔpCO ₂ was obtained from the difference in pCO ₂ in the arterial line at baseline (pCO ₂ T1) and after 5 min of hemodialysis (pCO ₂ T2). ∆pCO ₂  = pCO ₂ T2-pCO ₂ T1.
Findings: In 70 hemodialysis patients (mean age: 70.52 ± 13.97 years; hemodialysis vintage of 41.36 ± 34.54, KT/V 1.4 ± 0.3), ∆pCO ₂ was 4 ± 4 mmHg, and urea recirculation was 7% ± 9%. Vascular access recirculation was identified using both methods in 17 of 70 patients, who showed a ∆pCO ₂ of 10 ± 5 mmHg and urea recirculation of 20% ± 9%; time in months of hemodialysis was the only difference between vascular access recirculation and non-vascular access recirculation patients (22 ± 19 vs. 46 ± 36, p: 0.05). In the non-vascular access recirculation group, the average ΔpCO ₂ was 1.9 ± 2 (p: 0.001), and the urea recirculation % was 2.8 ± 3 (p: 0.001). The ΔpCO ₂ correlated with the urea recirculation % (R: 0.728; p < 0.001).
Discussion: ΔpCO ₂ in the arterial blood line during hemodialysis is an effective and reliable diagnostic tool for identifying recirculation of the vascular access but not its magnitude. The ΔpCO ₂ test application is simple and economical and does not require special equipment.
(© 2023 The Authors. Hemodialysis International published by Wiley Periodicals LLC on behalf of International Society for Hemodialysis.)