The relationship between the flow of arteriovenous fistula and cardiac output in haemodialysis patients

Background. Satisfactory haemodialysis (HD) vascular access flow (Qa) is necessary for dialysis adequacy. High Qa is postulated to increase cardiac output (CO) and cause high-output cardiac failure. Aim of the present prospective study was to evaluate the relationship between Qa of arteriovenous fistulas (AVFs) and CO in order to have a closer insight into this scarcely explored aspect of HD pathophysiology. Methods. Ninety-six patients bearing an AVF entered the study. All were evaluated a priori for the existence of cardiac failure according to the functional classification of the American College of Cardiology/American Heart Association task force. Qa and CO were measured by means of the ultrasound dilution Transonic Hemodialysis Monitor HD02. Results. The mean Qa of the 65 lower arm AVFs was 0.948 +/- 0.428 SD 1/min, whereas that of the 31 upper arm AVFs was 1.58 +/- 0.553 1/min. The difference was statistically significant (P < 0.001). Ten patients were classified as having high-output cardiac failure; seven of them bore an upper arm AVF. Thus, upper arm AVFs were associated with an increased risk of high-output cardiac failure (P < 0.04, chi(2) test). A third-order polynomial regression model best fitted the relationship between Qa and CO. The analysis of the regression equation identified 0.95 and 2.21/min as Qa cut-off points. The receiver operating characteristic curve analysis showed that Qa values >= 2.01/min predicted the occurrence of high-output cardiac failure more accurately than two other Qa values ( sensitivity 89%, specificity 100%, curve area 0.99) and three Qa/CO ratio values (cardio-pulmonary recirculation-CPR). The better performance among the latter was that of CPR values >= 20% ( sensitivity 100%, specificity 74.7%, curve area 0.92). Conclusions. Our prospective study shows that the relationship between Qa of AVFs and CO is complex and a third-order polynomial regression model best fits this relationship. Furthermore, it is the first study to clearly show the high predictive power for high-output cardiac failure occurrence of Qa cut-off values 2.0 l/min.