Researchers behind a new study published in the Annals of Vascular Surgery, among them lead author Laura Anderson and corresponding author Benjamin Brooke (both University of Utah Health, Salt Lake City, USA), have found that severe obesity risks a greater likelihood of maturation failure in the arteriovenous fistulas (AVFs) of patients looking to start dialysis.
Their work cites a 2008 Kidney International-published meta-analysis by Y Wang (Johns Hopkins University, Baltimore, USA) et al, which suggested that 33% of all US cases of end-stage kidney disease (ESKD) are associated with obesity and metabolic syndrome. Anderson and colleagues further aver that there has been a 42% increase in ESKD cases in the USA, which significantly includes a sevenfold increased risk of developing the condition for those with a body mass index (BMI) ≥35.
In reviewing the existing literature, the authors of this study note that, while some research has found higher AVF patency rates for obese patients, other research has found higher rates of failure and stenosis. Anderson and colleagues sought to clarify the effect of a BMI ≥35, “the most severe classes of obesity”, with a view to facilitating better clinical decision-making.
They conducted a retrospective cohort study, analysing the data from patients who received either a radiocephalic, brachiocephalic, or brachiobasilic AVF at a single centre during the period 2016–2019. The primary outcome was functional maturation following AVF creation, defined as use of the AVF with two needles for 75% of dialysis sessions in a continuous four-week period. Secondary outcomes included AVF depth and diameter, as well as flow volume, which was measured using a postoperative ultrasound examination.
A total of 426 AVF procedures were performed during the study period, with 202 available for analysis following the exclusion criteria. Among these were 49 (24%) with radiocephalic, 87 (43%) with brachiocephalic, and 66 (33%) with brachiobasilic AVFs. Stratification by BMI yielded 53 patients (26%) in the severely obese group and 149 (74%) in the remaining categories. There were “no significant differences” between the groups on other factors, apart from a higher percentage of female patients in the former group.
The authors found a “significantly lower rate of functional maturation” in the severely obese group (58% severe obesity vs. 80% non-severe obesity; p=0.002). A subanalysis by fistula type found that differences in primary and assisted maturation between obesity groups on brachiocephalic AVFs were significant, but were not so for those with radiocephalic and brachiobasilic AVFs.
On the secondary outcomes, outflow average vein depth was “significantly increased” in severely obese patients compared to the other groups, with the difference marked across all three types of AVF (p<0.05 for all comparisons). There was also a statistically significant larger average vein diameter for those severely obese patients with brachiocephalic AVFs (6.8mm severe obesity vs. 5.9mm non-severe obesity; p=0.007). The authors did not find significant differences in flow volume for any AVF type between any of the groups.
Multivariable logistic regression analyses, which controlled for a variety of other factors including sex, age, smoking status, and AVF type, found that severely obese patients were 62% less likely to achieve functional maturation than AVFs in patients with BMI ≤34.9 (odds ratio [OR] 0.38; 95% confidence interval [CI] 0.18-0.78, p=0.009).
The data suggest that obesity is of greatest concern in fistula maturation for severely obese patients with a brachiocephalic fistula, the authors say in their discussion, adding that it can also impact brachiobasilic AVFs “even after transposition”. Drawing attention to the “obesity paradox”, the finding of some studies that patients with higher BMIs have better survival rates with ESKD, sometimes attributed to “nutritional preserve and protection against wasting in the setting of acute illness”, they argue that their results indicate that this does not extend to fistula maturation. For treatment of severely obese patients with an AVF who cannot be cannulated, Anderson et al note that transposition and superficialisation of the fistula are established options.
Outlining some limitations, including the retrospective cohort design of their study and its focus on functional maturation outcomes rather than primary or secondary patency, the authors nevertheless conclude that their results support the claim that BMI ≥35 reduces functional maturation rates. “These data,” they state finally, “can help guide decision making when planning AVF placement in severely obese patients, which should include scheduling adjuvant superficialisation procedures on appropriate patients.”