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13-03-2013 | Surgery | Article

Surgical volumes effect challenged

Abstract

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medwireNews: Case mix may be largely responsible for the supposed effect of operator volumes on surgical outcomes, a prospective, single-center study suggests.

Researchers found that the relationship between annual carotid endarterectomy (CEA) volumes of the surgeons and patient outcomes disappeared after accounting for American Society of Anesthesiologists' (ASA) category (ie, how ill the patients were before surgery).

The association between case volume and outcomes "has led some to argue for selective referral to high-volume surgeons," notes Christopher Abularrage (Johns Hopkins Hospital, Baltimore, Maryland, USA) in an invited critique on the paper published in JAMA Surgery.

The relationship was established mainly in retrospective analyses of large administrative databases. The present study, by Matthew Maas (Northwestern University, Chicago, Illinois, USA) and colleagues, is smaller, but uses hospital-level data from Massachusetts General Hospital in Boston, which Abularrage says allows "a more in-depth analysis of patient-specific variables lost in the billing coding scheme used to populate administrative databases."

The study includes 841 patients who underwent CEA from 2008 through 2010. In line with previous research, the team found an increased 30-day stroke and death rate if patients were operated on by low-volume surgeons (=40 cases/year) rather than higher-volume surgeons, at 6.9% versus 2.0%. The same pattern was evident for the 30-day complication rate, at 13.4% versus 7.2%.

This equated to a more than threefold increased risk for stroke or death with low- versus higher-volume surgeons, and the association remained after accounting for variables used in a previous large administrative database study, by Birkmeyer et al published in The New England Journal of Medicine.

"That study was selected because it is the most heavily cited publication addressing this question, and the authors explicitly argued for the theoretical adequacy of their risk adjustment technique in the face of prior criticisms," comment Maas and team.

But their hospital-level study reveals that low-volume surgeons performed fewer elective cases than higher-volume surgeons, at 64.2% versus 71.6%, and more often operated on symptomatic patients, at 35.8% versus 28.6%. When the researchers adjusted for additional variables, including ASA category, the association between low-volume surgeons and stroke/death risk reduced to a nonsignificant odds ratio of 1.65 (confidence interval 0.59-4.64).

By contrast, higher ASA category was associated with a significant 2.78-fold increased risk for 30-day stroke or death after accounting for confounders.

"A true relationship between surgeon volume and outcomes remains uncertain, and caution is advised in developing policies based on these findings," conclude Maas et al.

They add: "Restricting CEA to high-volume surgeons at our institution could lead to limited access to care for the greater proportion of urgent cases managed by low-volume surgeons, without leading to improved outcomes."

By Eleanor McDermid, Senior medwireNews Reporter

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