Disparities in Fistula Maturation Persist Despite Preoperative Vascular Mapping

Concise Methods

Results

The clinical characteristics of the study population are summarized in Table 1. More than half of the patients were male, and approximately one quarter were ≥65 yr of age. The majority of patients were black, reflecting the demographic composition of our dialysis population. Diabetes, vascular disease, and congestive heart failure were common. A similar proportion of patients had a fistula placed in the upper arm and in the forearm.

The overall primary failure rate of fistulas was 40% (82 of 205 patients). Univariate logistic regression analysis was performed to determine which factors were associated with primary fistula failure. Older age, female gender, and forearm location each were associated with a significantly higher risk for primary fistula failure (Table 2). In contrast, obesity, diabetes, coronary artery disease, peripheral vascular disease, congestive heart failure, and previous access were not significantly associated with fistula outcome. On multiple variable logistic regression modeling, patient age, gender, and fistula location were together predictive of primary fistula failure (Table 3). The impact of each of these variables on fistula outcome is illustrated in Figure 1. The primary failure rate varied greatly, from a low of 22% in younger men who received an upper arm fistula to a high of 78% in older women who received a forearm fistula.

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Figure 1.

Primary fistula failure, sorted by age, gender, and fistula location. Older age, female gender, and forearm location each were associated with a higher risk for failure to mature.

The preoperative vascular diameters were compared among patient subsets (Table 4). The arterial and venous diameters were similar in older and younger patients, regardless of whether forearm or upper arm fistulas were examined. The arterial diameters were significantly lower in women than in men, both for forearm and upper arm fistulas; however, the arterial diameters were similar in women whose fistulas failed to mature and in those with successful fistulas (2.4 ± 0.4 versus 2.3 ± 0.4 mm [P = 0.55] for forearm fistulas; 5.0 ± 1.0 versus 5.1 ± 1.4 mm [P = 0.86] for upper arm fistulas). The venous diameters did not differ between women and men.

Dynamic vascular measurements were obtained for 72 patients who received a forearm fistula. This patient group had a mean age of 51 ± 15 yr; 67% were male, 86% were black, 44% had diabetes, 25% had coronary artery disease, 8% had peripheral vascular disease, 22% had congestive heart failure, and 28% were obese. The preoperative dynamic vascular measurements were compared between forearm fistulas that were successfully used for dialysis (mature) and those that failed to mature (Table 5). The absolute values of PSV, EDV, and RI measured during sustained fist clenching or after release of fist clenching did not differ significantly between immature and mature fistulas. Similarly, there was no difference in PSV or RI between successful and unsuccessful fistulas; however, the high variability in measurements among individual patients may have obscured small differences.

Discussion

The overall frequency of primary fistula failure remained high despite routine preoperative vascular mapping and attempts to salvage immature fistulas by radiologic or surgical interventions. There were striking variations in the primary fistula failure rate among patient subgroups: Failure to mature was more common in women than in men, in older than in younger patients, and in forearm than in upper arm fistulas. Moreover, these three clinical variables had a cumulative interaction on fistula outcomes. Thus, the failure to mature rate varied from a low of 22% in younger men who received an upper arm fistula to a high of 78% in older women who received a forearm fistula.

Women had a higher primary fistula failure rate than men and also had significantly smaller preoperative arterial diameters than men. Thus, one could postulate that the lower arterial diameters were responsible for the lower fistula success rate in female patients. This seems unlikely, given that the arterial diameters were not different in women whose fistulas failed to mature and in those with mature fistulas. In fact, among patients <65 yr of age, the primary failure rate was higher in women who received an upper arm fistula than in men who received a forearm fistula (47 versus 31%; Figure 1), even though the former had higher arterial diameters (Table 4). Moreover, the primary failure rate of forearm fistulas in the pediatric population is 33% despite the small vessel size (16).

These disparities suggest that successful fistula maturation is not determined exclusively by the diameters of the artery and vein used to create the fistula. Rather, it is likely that the ability of fistulas to dilate (vascular compliance) varies substantially by patient age and gender. How best to determine vascular compliance preoperatively remains a subject of investigation. Lockhart et al. (12) correlated preoperative changes in PSV after fist clenching with clinical fistula outcomes in 89 patients who received a forearm fistula. Neither the absolute PSV nor its change after fist clenching predicted fistula maturation in the overall group. In a post hoc analysis, a lack of increase in PSV was associated with a lower likelihood of fistula maturation in female but not in male patients. The lack of association between dynamic vascular measurements and clinical fistula outcomes in this study is in agreement with the previous pilot data from our institution (12). Another pilot study used strain-gauge plethysmography to measure venous distensibility in 17 patients who were scheduled for placement of a forearm fistula (17). Patients whose fistula matured had a higher distensibility score than those whose fistula failed to mature. Extensive multicenter studies are needed to assess the predictive value of various dynamic vascular measurements for clinical maturation of both forearm and upper arm fistulas.

This study has a number of limitations. First, the fistula outcomes were determined retrospectively; however, a prospective, computerized vascular access database was used to collect this information, giving a high level of confidence that the data were complete and accurate. Second, these observations were obtained from a single dialysis center, and they may not generalize to some dialysis centers. Third, because our dialysis population has very few white patients, it was not possible to draw meaningful conclusions on differences in fistula maturation between white and black patients; however, a recent multicenter, observational study observed a higher rate of primary fistula failure rate in nonwhite as compared with white patients (4). Fourth, we did not find a significant association between fistula maturation and peripheral vascular disease or coronary artery disease, in contrast to a large, multicenter, observational trial (4). The smaller sample size may have obscured this association in this investigation. Finally, the relatively high primary fistula failure rate at our teaching institution may in part reflect inferior clinical outcomes of fistulas placed by trainees.

Conclusions

Despite routine preoperative vascular mapping, disparities in fistula maturation persist. Specifically, a higher likelihood of primary fistula failure is observed in women, older patients, and forearm fistulas. These discrepancies suggest that functional properties of the vessels may contribute to fistula failure to mature even when the diameters are adequate.

Disclosures

None.