Rethinking the High-Volumes/Best-Outcomes CV-Surgery Formula

Shelley Wood

December 11, 2013

CHICAGO, IL (updated December 12, 2013) — A new analysis of mortality rates following cardiovascular surgery offers some fresh insights into what drives the higher mortality at hospitals that perform fewer CV surgeries and may prompt a rethink of the so-called "volume effect"[1].

Based on their findings, Dr Andrew Gonzalez (University of Illinois Hospital, Chicago) and colleagues argue that to improve CV-surgery outcomes, the focus should shift from the perioperative period to postoperative care.

Speaking with heartwire , senior author Dr Amir Ghaferi (University of Michigan, Ann Arbor) noted that for many patients, the perioperative phase is something of a "honeymoon period," where they seem to be fine. What typically happens is that a patient will develop a complication, even something minor like a urinary-tract infection, that goes unnoticed. "People tend to fail to recognize that in a timely or quick fashion, and that's where the dominoes start to fall, and patients go down this slippery slope of one complication followed by another complication, ultimately reaching the point of no return. . . . So the key is stopping that first complication from triggering that domino effect."

Their study used patient-level data from almost 120 000 Medicare patients who underwent CABG, aortic-valve repair (AVR), or abdominal aortic aneurysm (AAA) repair over a two-year period (2005–2006).

They found that, as has been documented across surgery specializations, hospitals that performed the highest volume of procedures also had the lowest mortality rates for all three procedures.

Of note, however, rates of major complications, most strikingly for CABG and AVR, were similar between the high- and low-volume hospitals. Where differences emerged, they note, was in so-called "failure to rescue"—that is, mortality following a major complication.

For example, rates of any major complication (pulmonary failure, pneumonia, MI, deep vein thrombosis [DVT] or pulmonary embolism [PE], acute renal failure, GI bleeding, postoperative hemorrhage, and surgical-site infection) were identical between the highest-volume hospitals and the lowest-volume hospitals, occurring at a rate of 28%. But failure to rescue from complications was statistically more common at the very low-volume hospitals (13.3%) than at the very high-volume hospitals (10.9%) (odds ratio 1.26, 95% CI 1.17–1.35).

"This suggests that developing a postoperative complication is not irrevocably fatal," Gonzalez et al write. "Although the critical opportunity may be further along the continuum of patient care than previously thought, it still relies on quickly recognizing and treating complications. In devising quality-improvement strategies for low-volume hospitals, future studies should first examine why high-volume hospitals are better able to execute such rescues."

"We're not advocating against making every effort to prevent complications; obviously, that's very important," said Ghaferi. "But many hospitals are doing a very good job of implementing evidence-based practices to prevent the most common complications. The majority of people, for example, know that giving DVT prophylaxis is very important. But what I'm saying is that we need to invest and focus a little bit more in that postoperative period as well. We tend to be very reactionary when we need to be more proactive."

In an accompanying commentary[2], Dr Lillian Kao (University of Texas Health Science Center, Houston) notes that although large data-set analyses such as Gonzalez et al's can help generate hypotheses that may lead to improved patient outcomes, they lack the granularity to determine what the actual causes of "failure to rescue" may be.

"Researchers need to move beyond documenting associations to performing hospital- and patient-level studies to understand where and why failures to rescue occur and how they can be prevented," she writes. "Delay in diagnosing and treating complications may be related to processes, structure, or both."

In fact, says Ghaferi, he and his colleagues are already investigating next steps, trying to identify links between failure to rescue and specific patient-level characteristics. "Right now in Michigan, we are going into hospitals and trying to figure out what it is about some of the microsystem resources and microsystem environments—the safety culture, attitudes, and practices—that are key to the rescue process."

Gonzalez and Ghaferi had no conflicts of interest; disclosures for the study coauthors are listed in the paper. Kao had no conflicts of interest.

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