• Emily V A Finlayson, John D Birkmeyer, Therese A Stukel, Andrea E Siewers, F Lee Lucas, and David E Wennberg.
• VA Outcomes Group, Department of Veterans Affairs Medical Center, White River Junction, VT 05009, USA.
• Surgery. 2002 Nov 1; 132 (5): 787-94.

AbstractBackground. Studies of medical admissions have questioned the validity of using claims data to adjust for preexisting medical conditions (comorbidities), but the impact of using comorbidities from claims data to risk-adjust mortality rates for high-risk surgery is not well characterized. The purpose of this study was to evaluate the relationship between comorbidities and mortality in administrative data in surgical populations and identify better risk-adjustment methods. Methods. Using the national Medicare database (1994-1997), we identified admissions for elective abdominal aortic aneurysm repair (140,577) and pancreaticoduodenectomy (10,530). We calculated the relative risk of mortality (adjusted for age, sex, race, and admission acuity) for 5 chronic conditions that are known (from clinical series) to increase the risk of postoperative mortality and are commonly used in claims-based risk-adjustment models. To explore the potential value of alternative risk-adjustment strategies, we examined relationships between surgical mortality and comorbidities using diagnosis codes identified from previous admissions. Results. Overall, in-hospital mortality for elective abdominal aortic aneurysm (AAA) repair and pancreaticoduodenectomy were 5.1% and 10.4%, respectively. For both procedures, 3 of the 5 comorbidities were associated with decreased risk of mortality: prior myocardial infarction (MI) [RR = 0.38; 95% confidence interval (CI), 0.33-0.43 for AAA; RR = 0.38; 95% CI, 0.21-0.69 for pancreaticoduodenectomy), malignancy (RR = 0.67; 95% CI, 0.59-0.76 for AAA; RR = 0.74; 95% CI, 0.45-1.21 for pancreaticoduodenectomy], and diabetes (RR = 0.76; 95% CI, 0.64-0.84 for AAA; RR = 0.59; 95% CI, 0.49-0.69 for pancreaticoduodenectomy). Using comorbidities identified from prior admissions increased the mortality risk estimates for prior MI (RR = 1.22; 95% CI, 1.08-1.38 for AAA; RR = 0.80; 95% CI, 0.49-1.30 for pancreaticoduodenectomy) and diabetes (RR = 1.41; 95% CI, 1.25-1.59 for AAA; RR = 0.94; 95% CI, 0.78-1.14 for pancreaticoduodenectomy). Conclusions. Because comorbidities coded on the index admission appear protective, incorporating them in risk-adjustment models for studies comparing surgical performance may penalize providers for taking care of sicker patients. When available, comorbidity information from prior hospitalizations may be more useful for risk adjustment.

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