Clinical studies have shown that patient- and hospital-level factors often play a significant role in surgical outcomes, particularly mortality, for both general surgeries and vascular surgical procedures. “Although patient-level factors affecting outcomes after open and endovascular abdominal aortic aneurysm (AAA) repair are well described, few studies have examined the impact of hospital-level factors on mortality after these procedures,” says Caitlin W. Hicks, MD, MS.

Previous research has indicated that mortality following open AAA repair (OAR) performed at high-volume hospitals is lower than that of OAR performed at low-volume institutions. Expert groups like the Leapfrog Group have advocated for a minimum volume criterion of 50 OAR cases or more per year as part of an evidence-based hospital referral safety standard. However, the effect of hospital volume on elective endovascular AAA repair (EVAR) is currently unclear.

“There has been a recent push to move AAA repairs to Aortic Centers of Excellence, in which elective AAA patients are triaged to high-volume academic centers,” Mahmoud B. Malas, MD, MHS says. “While such initiatives are expected to improve outcomes, it’s important to understand how hospital-level factors may impact postoperative outcomes before this step can be taken.” To address this issue, Dr. Malas, Dr. Hicks, and colleagues had a preliminary analysis published in JAMA Surgery that explored the role of specific hospital effects on mortality following OAR and EVAR.


Preliminary Research

In the retrospective analysis, the study team used the American College of Surgeons’ National Surgical Quality Improvement Program database, examining patients undergoing OAR or EVAR over a period of about 2.5 years. The group then compared 30-day expected mortality ratios based on hospital type (academic vs community) and size (100 to 299 beds vs 300 to 500 beds vs more than 500 beds). Data were available on 11,250 patients, with 2,466 undergoing OAR and 8,784 undergoing EVAR.

According to the results, the overall 30-day mortality was 14.0% for OAR and 4.3% for EVAR. The findings suggest that outcomes for both OAR and EVAR appear to depend greatly on hospital-level effects. “For all outcomes, academic hospital type was the single most significant predictor of reduced mortality following AAA repair,” says Dr. Malas (Figure). “Hospital size significantly affected mortality for OAR, with death rates increasing significantly as the hospital size decreased. On the other hand, hospital type significantly affected mortality for EVAR.” The 30-day mortality for EVAR was 2.6% for academic hospitals, compared with a rate of 11.2% observed at community hospitals.

Dr. Hicks notes that the study group surprisingly observed no significant differences in outcomes after EVAR when comparing high- and low-volume hospitals. “This lack of volume effect may be the result of a case mix bias that tends to be higher in larger hospitals,” she says. “If future research can better account for patient complexity, we expect that hospital volume would end up being more important for EVAR than it was in our study.”

The association between hospital volume and mortality in the study is consistent with previous reports, according to the investigators. Research has consistently shown a strong link between hospital volume and outcomes following AAA repair that favors high-volume hospitals, especially in OAR cases.


Validation Needed

Dr. Malas says the findings suggest that—in addition to hospital-level factors playing an important role in determining patient outcomes after AAA repair—the data support the notion that Aortic Centers of Excellence may help improve outcomes. He cautions, however, that the data are preliminary. “We need to validate our findings in a cohort that allows for consideration of both patient complexity and hospital factors,” he says. The relative safety of EVAR and OAR may depend on appropriate patient selection and adequate access to multidisciplinary care in order to minimize failure to rescue rates and improve survival. Other factors that may enhance outcomes include dedicating resources and ensuring ICU monitoring of patients after their operation.

By regionalizing AAA repairs to Aortic Centers of Excellence, it may be possible to reduce failure to rescue events and thereby improve mortality rates following elective AAA repair on a national level. “Although these data make a preliminary argument in favor of Aortic Centers of Excellence, we need more research,” Dr. Hicks says. “We need comprehensive studies that help us determine the specific factors that have the greatest impact on outcomes after these surgeries.” Dr. Hicks adds that she and her colleagues recently presented data from a study to this effect at the 2015 annual meeting of the Eastern Vascular Society Meeting. She is hopeful that results of this analysis will be published in the near future and will provide more insight on the topic.


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