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The volume-outcome effect for abdominal aortic surgery: differences in case-mix or complications?
Justin B Dimick1, Peter J Pronovost, John A Cowan
1Department of Surgery, University of Michigan Medical Center, 1500 E Medical Center Drive, Taubman Center 2210, Ann Arbor, MI 48109-0329, USA.
Archives of Surgery (Chicago, Ill. : 1960)
|July 3, 2002
Summary
Hospital volume impacts abdominal aortic surgery mortality primarily through postoperative complications, not patient case-mix. Reducing complications can lower mortality rates at lower-volume hospitals.
Area of Science:
- Vascular Surgery
- Health Services Research
- Outcomes Research
Background:
- High-volume hospitals demonstrate lower operative mortality for complex vascular procedures compared to low-volume facilities.
- Disparities in postoperative complication rates may account for variations in mortality observed between hospitals of differing surgical volumes.
Purpose of the Study:
- To investigate the relationship between hospital surgical volume and in-hospital mortality after abdominal aortic surgery.
- To determine whether postoperative complications mediate the association between hospital volume and mortality.
Main Methods:
- Adult patients (N=2987) undergoing abdominal aortic surgery in Maryland (1994-1996) were analyzed.
- Multiple logistic regression models were employed to assess in-hospital mortality, adjusting for patient case-mix and specific postoperative complications.
- Two sequential analyses were conducted to evaluate the independent and combined effects of hospital volume and complications on mortality.
Main Results:
- High-volume hospitals exhibited significantly lower mortality rates (5.6%) compared to medium (6.8%) and low-volume (8.7%) hospitals (P=.03).
- After adjusting for case-mix, high surgical volume was associated with a 37% reduction in mortality (OR, 0.63; 95% CI, 0.42-0.92).
- Patients at high-volume hospitals experienced reduced risks of pulmonary failure, reintubation, pneumonia, cardiac complications, and shock. When complications were included in the model, hospital volume was no longer a significant predictor of mortality.
Conclusions:
- The observed association between hospital volume and reduced mortality in abdominal aortic surgery is mediated by differences in postoperative complication rates.
- Preoperative patient case-mix does not explain the mortality differences attributed to hospital volume.
- Targeted interventions to decrease postoperative complications may improve outcomes at low-volume hospitals and reduce overall mortality.