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Researchers find overall inverse relationship between hospital volume, preventable adverse events for three major surgical procedures

Wednesday, April 11 2012 | Comments
Evidence Grade 0 What's This?
Using patient safety indicators (PSIs) developed by the Agency for Healthcare Research and Quality to identify hospital-acquired adverse events, researchers at Stanford University showed that hospitals that perform a high volume of three different types of surgical procedures have significantly lower risk-adjusted rates of associated preventable adverse events as compared with hospitals that perform a lower volume of the same procedures.

Data for the observational study were obtained from the Nationwide Inpatient Sample discharge database for the years 2005 through 2008.

The study sample included 182,843 adults who underwent surgery to repair an abdominal aortic aneurysm (AAA), almost 1.1 million adults who underwent coronary-artery bypass grafting (CABG) and 354,478 adults who had Roux-en-Y gastric bypass (RNYGB) surgery for obesity (rather than for a malignant neoplasm of the digestive organs). The researchers explained that they chose these three procedures for the analysis because they have "a sizeable volume-outcomes relationship, established hospital volume standards …, large enough cohorts to detect adverse events and represent a variety of major surgical fields."

The researchers noted that 26 percent of the AAA procedures, 16 percent of the CABG surgeries and 22 percent of the RNYBG procedures were performed at high-volume hospitals (i.e., those in the top tercile for each type of procedure). For all three types of procedures, the high-volume hospitals had significantly lower risk-adjusted rates of inpatient mortality as compared with hospitals ranking in the bottom two terciles for volume. 

When the researchers compared risk-adjusted PSI rates per 1,000 admissions during the four-year study period among the high-, mid- and low-volume hospitals for each of the three types of procedures, they observed an overall dose-response effect (i.e., the PSI rate decreased from low- to mid-volume hospitals and from mid- to high-volume hospitals).

For the AAA procedure, the dose-response effect was observed for three of the nine PSIs associated with that type of surgery, and for CABG, the dose-response effect was observed for six of nine PSIs. For RNYBG surgery, the dose-response effect was observed for eight of nine PSIs.
The percentage of patients with one or more PSI was significantly higher for low-volume hospitals relative to high-volume hospitals for all three types of procedure. Specifically, for AAA repair, the proportion of patients with at least one PSI was 8.8 percent at low-volume hospitals, 7.8 percent at mid-volume hospitals and 7.2 percent at high-volume hospitals. The corresponding proportions for CABG were 4.4 percent, 4.4 percent and 4.1 percent, and for RNYBG, 6.1 percent, 2.8 percent and 2.1 percent.

"Lower mortality and adverse events at high-volume hospitals is likely dependent on a multitude of factors, including patient selection, technical skill, anesthesia support and postoperative care," the study authors remarked. "The quality of care rendered on the basis of volume is likely a continuum and not simply a threshold number. More research in the nascent field of quality improvement and patient safety is required for better understanding of the specific drivers of the volume-outcome relationship."

These study results were published in the April issue of the journal Health Services Research.

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