pCO₂ Reveals Arteriovenous Fistula Recirculation in Bicarbonate Hemodialysis (RecirCO₂lation Test)

Abstract

We propose arterial pCO₂ as test to discover vascular access recirculation (VAR) in bicarbonate hemodialysis (HD). We selected 30 HD patients with a ascertained well-functioning arteriovenous fistula (Control). In these patients, we artificially created VAR through the reversion of HD lines (Reversed). Results of the arterial gas analysis were collected at the start of HD (baseline) and after 5 min. At baseline, no differences of pH, pCO₂ and HCO₃ were found between the 2 groups. At 5 min, pCO₂ increased from 38.1 ± 3.3 to 47.2 ± 6.3 mm Hg (p < 0.0001) in Reversed, whereas no increase was found in Control (p = 0.052). Areas under curve of pCO₂-increase was 0.96 (0.91-1.00) and pCO₂ at 5 min 0.92 (0.85-0.98). pCO₂-increase >4.5 mm Hg showed sensitivity 86.7% and specificity 100% with positive predictive value (PPV) 100% and negative predictive value (NPV) 89%. A pCO₂ value above 43 mm Hg at 5 min showed sensitivity 80%, specificity 90%, PPV 89%, NPV 82%. pCO₂ increase >4.5 mm Hg and/or pCO₂ at 5 min >43 mm Hg may accurately detect VAR.

Acid‐base homeostasis during hemodialysis: New insights into the mystery of bicarbonate disappearance during treatment

“…Blood PCO 2 increases from 36 to 38 mm Hg within the first 15 minutes, and then does not change further until the end of dialysis when it returns to 36 mm Hg. These changes were not statistically significant, but the pattern of change is consistent with previous observations …”

“…In either case, organic acid production causes an extra burden on the patient, because the CO 2 produced by the reaction with HCO 3 − adds to the excretory work of the lungs. This workload contributes to the small increase in blood PCO 2 that is characteristic of patients receiving hemodialysis . Finally, as noted earlier, the reaction results in an irreversible loss of alkali during hemodialysis.…”

Dialysis-Related Acidemia and Acidosis by Dialysate: The Forgotten Issue of CO₂ Overload from Dialysate

“…If dialysis-related acidemia is found in the arterial line, then vascular access should be inspected for correct needle placement or fistula malfunction because recirculation occurs when blood exiting the filter is not flowing into systemic blood but is reentering the extracorporeal circuit [9] . A more serious problem can occur if dialysisrelated acidemia of venous line is coupled with underlying pulmonary or cardiac disease.…”

How to Reduce the Risk of Arteriovenous Fistula Dysfunction by Observing Prepump Arterial Pressure during Hemodialysis: A Multicenter Retrospective Study

“…Moreover, when outflow tract stenosis occurs, slower blood flow and access recirculation are more likely to cause thrombus formation and cause AVF dysfunction. The ultrasound dilution technique or observations combined with measurements of the change in Kt/V and blood gas analysis are recommended to determine if access recirculation has occurred [29-31]. A reference for clinical practice based on this value needs to be established in the future.…”