Modeling Survival of Arteriovenous Accesses for Hemodialysis: Semiparametric versus Parametric Methods

Background and objectives: Comparing outcomes of arteriovenous grafts and fistulas is challenging because the pathophysiology of access dysfunction and failure rate profiles differ by access type. Studying how risks vary over time may be important. Design, setting, participants, & measurements: Longitudinal data from 535 incident hemodialysis patients were used to study the relationship between access type and access survival, without (semiparametric Cox modeling) and with specification of the underlying hazard function (parametric Weibull modeling). Results: The hazard for failure of fistulas and grafts declined over time, becoming proportional only after 3 months from surgery, with a graft versus fistula hazard ratio of 3.2 (95% confidence interval 1.9 to 5.3; Cox and Weibull estimation) and time ratio of 0.11 (i.e., the estimated access survival time was approximately one tenth shorter in grafts; 95% confidence interval 0.04 to 0.28; Weibull estimation only). Considering the entire observation period, grafts had slower hazard decline (P < 0.001) with shorter median survival times than fistulas (8.4 versus 38.3 months; Weibull regression only). Conclusions: Parametric models of arteriovenous access survival may provide relevant information about temporal risk profiles and predicted survival times.