Factors associated with access blood flow in native vessel arteriovenous fistulae

Access blood flow (Qa) identifies stenosis in patients with native vessel AV fistulae (AVF), but data on factors that are associated with Qa in normally functioning accesses are sparse. Such factors could be used in conjunction with Qa to improve the diagnostic performance of screening. We examined the relationship between Qa and certain clinical characteristics in a large group of patients with AVF.

This was a retrospective study of incident and prevalent haemodialysis patients treated at a single institution, all of whom had a functioning AVF during the study period. Qa was measured bimonthly using ultrasound dilution in all subjects. Mixed models were used to explore the relationship between Qa and a group of independent variables, including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), diabetes mellitus, patient age, sex, height, body mass index (BMI) and AVF location (forearm vs upper arm).

A total of 4084 Qa measurements was made in 294 patients. Univariate analysis found that younger patient age, non-diabetic status, higher blood pressure (SBP, DBP, MAP, all at the time of Qa measurement), upper arm AVF location and overweight status (BMI >/=25) were significantly associated with Qa. SBP appeared to be more strongly associated with Qa than either DBP or MAP. Patient sex, height and interval between access creation and Qa measurement were not significantly associated with Qa. Tests for interaction suggested that the association between SBP and age and Qa varied significantly by access location. In a multivariate model, SBP, overweight status and diabetic status were independently associated with Qa. The strength of the association between these characteristics and Qa appeared to be clinically relevant.

Our findings suggest that a single Qa threshold for angiography in all patients may be simplistic, and that the optimal threshold might vary by patient subgroup. The strong association between SBP and Qa suggests that adjusting Qa for SBP may improve the specificity of access screening. Further work is required to determine whether such modifications to current practice would improve the predictive power of Qa measurements for detection of stenosis in AVF.