Diagnostic accuracy of arterial line blood gas measurements as an estimate of arteriovenous fistula recirculation

Aim We studied the diagnostic accuracy of blood gas determination as a novel method for the estimation of arteriovenous fistula ( AVF ) recirculation ( RC ). Methods In 25 patients on chronic haemodialysis, with failure of a previously well functioning native AVF (mean two‐needle urea‐based RC : 41 ± 10%), arterial line ( AL ) as well as a peripheral vein ( PV ) blood samples drawn by the end of a 4 h haemodialysis session, before and after the surgical repair of their AVF . Results Compared to PV samples, patients with RC had significantly higher AL blood pCO 2 and pO 2 values ( P  < 0.001) and lower AL blood pH and K + values ( P  < 0.001), findings that were reversed after the surgical restoration of adequate AVF function. On regression analysis, urea RC values were correlated positively with AL pCO 2 values (r = 0.683, P  < 0.001) and negatively with AL pH values (r = 0.896, P  < 0.001). AL pCO 2  > 40 mmHg was shown to have the best sensitivity and AL pH  < 7.25 the best specificity. RC index, that is, the AL pCO 2 / pH ratio, was found to have superior test characteristics compared to pH and pCO 2 (sensitivity 95% and specificity 88% for values >5.5) making it a powerful diagnostic as well as screening tool. Conclusion We propose the regular AL blood gas measurement as a novel method of AVF function surveillance and RC diagnosis. AL blood pH  < 7.25, pCO 2  > 40 mmHg and RC index > 5.5, escorted by rather high pO 2 and low K + by the end of dialysis session, but probably earlier as well, signify an important RC (>20%) and warrant further investigation of AVF patency.