Razionale

Glucose infusion test (GIT) is  commonly used to asses vascular access recirculation (VAR) but it requires different times of sampling according to length of arterial line. In hemodialysis unit the availability of gas analyzer and of arterial samples makes blood gas analysis (BGA) frequently running.  Blood leaving the dialyzer has higher pCO₂ and HCO₃ values and lower pH than blood entering the dialyzer, because pCO₂ in dialysate amount to 100 mmHg and CO₂ has high dialysance.  In the case of VAR, recirculating blood reenters the extracorporeal circuit through the arterial needle, abnormally increasing pCO₂ and HCO₃ and decreasing pH in the arterial line blood. This picture, “non hypoxic respiratory acidosis”, could be a sign of recirculation.

Casistica e Metodi

BGA from arterial needle was obtained from 30 patients before bicarbonate-dialysis. Five minutes after beginning of treatment GIT and BGA from arterial line were performed. One week later the same protocol with reversed lines (i.e. arterial line connected to venous needle and vice versa) to create artificial recirculation was repeated. In addition BGA was also obtained after turned off  dialysate flow.

Risultati

GIT and pCO₂ increase, e.g. pCO₂ at 5” minus pCO₂ at baseline, strongly correlate (r=0.826, p<0.0001); The ROC curve analysis identifies a threshold value of pCO₂ increase ≥4.6 mmHg with (83% sensitivity and 97% specificity) for VAR. Notably the area under the ROC curve was 0.945 (CI95% from 0.892 to 0.997). When  dialysate flow was turned off  BGA parameters revert to baseline, confirming that pCO₂ increase was related to VAR.

Conclusioni

Increasing pCO₂ in arterial line could easily and accurately identify VAR as defined by GIT.

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