Evaluation of partial pressure CO 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 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 , so in the presence of recirculation, pCO2 in the arterial blood line may increase (ΔpCO ) during hemodialysis sessions. The aim of our study was to evaluate ΔpCO as a diagnostic tool for vascular access recirculation in chronic hemodialysis patients.

Methods: We evaluated vascular access recirculation with ΔpCO and compared it with the results of a urea recirculation test, which is the gold standard. ΔpCO was obtained from the difference in pCO in the arterial line at baseline (pCO T1) and after 5 min of hemodialysis (pCO T2). ∆pCO  = pCO T2-pCO 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 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 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 was 1.9 ± 2 (p: 0.001), and the urea recirculation % was 2.8 ± 3 (p: 0.001). The ΔpCO correlated with the urea recirculation % (R: 0.728; p < 0.001).

Discussion: ΔpCO 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 test application is simple and economical and does not require special equipment.