Abstract
Background. 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. (Surgery 2002;132:787-94)
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Article info
Publication history
Accepted:
April 26,
2002
Footnotes
*Supported by a grant from the Agency for Healthcare Research & Quality (R01 HS10141-01). Dr Birkmeyer was also supported by a Career Development Award from the VA Health Services Research & Development program. The views expressed herein do not necessarily represent the views of the Department of Veterans Affairs or the US government.
**Reprint requests: Emily V.A. Finlayson, MD, VA Outcomes Group (111B), Department of Veterans Affairs Medical Center, White River Junction, VT 05009.
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Copyright
© 2002 Mosby, Inc. Published by Elsevier Inc. All rights reserved.
