Evaluation of partial pressure CO2 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 pCO2, so in the presence of recirculation, pCO2 in the arterial blood line may increase (Delta pCO(2)) during hemodialysis sessions. The aim of our study was to evaluate Delta pCO(2) as a diagnostic tool for vascular access recirculation in chronic hemodialysis patients. Methods: We evaluated vascular access recirculation with Delta pCO(2) and compared it with the results of a urea recirculation test, which is the gold standard. Delta pCO(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)T.2). Delta 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), Delta 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 Delta 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 Delta pCO(2) was 1.9 +/- 2 (p: 0.001), and the urea recirculation % was 2.8 +/- 3 (p: 0.001). The Delta pCO(2) correlated with the urea recirculation % (R: 0.728; p < 0.001). Discussion: Delta pCO(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 Delta pCO(2) test application is simple and economical and does not require special equipment.