Does Quantity Mean Quality in Medical Procedures?

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The summary below is from the full report titled "Is Volume Related to Outcome in Health Care? A Systematic Review and Methodologic Critique of the Literature." It is in the 17 September 2002 issue of Annals of Internal Medicine (volume 137, pages 511-520). The authors are EA Halm, C Lee, and MR Chassin.

What is the problem and what is known about it so far?

Over the past 20 years, researchers and health care systems have had a growing interest in understanding what makes for high-quality care, with the ultimate goal of improving patient outcomes. One idea is that high volume may be linked to better outcomes ("practice makes perfect"). Many studies claim to have shown that patients under the care of physicians who frequently perform a particular surgery or other procedure are less likely to die or have complications. However, since other factors may influence patient care outcomes, it is difficult to be sure just how much of an effect high volume itself has.

Why did the authors do this review?

More and more studies are being done on the relationship between volume and outcome. However, differences in how the studies are done make it difficult to compare studies and draw conclusions. The authors set out to determine what general conclusions can be drawn about volume–outcome relationships. They also assessed how well studies on such relationships were done, including whether the researchers took into account patient characteristics that may affect results, such as age and illness.

How did the authors do this review?

The authors searched databases and consulted experts to find published studies on volume–outcome relationships for procedures done since 1980. One hundred thirty-five studies covering 27 different procedures were reviewed. The authors compared outcomes across studies. They defined outcome as the proportion of patients who died during or after a procedure.

What did the authors find?

Seventy percent of studies supported the idea that patients undergoing a procedure are less likely to die if their hospital or physician does large numbers of such procedures. This finding was strongest for AIDS treatment and for surgery on pancreatic cancer, esophageal cancer, abdominal aortic aneurysms, and pediatric heart problems. For these procedures, the authors estimated that using "low-volume" hospitals or physicians resulted in approximately 3 to 13 additional deaths per 100 patients. They found limited evidence and weaker volume–outcome relationships for heart surgery, surgery for other types of cancer, and orthopedic procedures. Most studies took into account patient characteristics such as age, but only 28% made statistical corrections that allowed them to compare low-volume and high-volume care in patients with similar general health, a factor that could affect the results of surgery.

What are the implications of the review?

The results suggest that for some but not all procedures, patients do better under the care of hospitals and physicians performing large numbers of that procedure. It is uncertain why higher volume is associated with better outcome. There is some evidence that high-volume providers are more likely to give patients effective treatments. Physicians' and hospitals' skills may improve when they do more procedures, and physicians may refer more patients to providers with better outcomes. Further studies are needed to explore the reasons behind volume–outcome relationships.