• Yue Li, Xueya Cai, Dana B Mukamel, and Peter Cram.
• Department of Community and Preventive Medicine, Division of Health Policy and Outcomes Research, University of Rochester, Rochester, NY 14642, USA. yue_li@urmc.rochester.edu
• Med Care. 2013 Jan 1; 51 (1): 45-51.

Objective: To determine the effect of postoperative length of stay (LOS) on 30-day readmission after coronary artery bypass surgery.Data Sources/Study Setting: We analyzed a final database consisting of Medicare claims of a cohort (N=157,070) of all fee-for-service beneficiaries undergoing bypass surgery during 2007-2008, the American Hospital Association annual survey file, and the rural urban commuting area file.Study Design: We regressed the probability of 30-day readmission on postoperative LOS using (1) a (naive) logit model that controlled for observed patient and hospital covariates only; and (2) a residual inclusion instrumental variable (IV) logit model that further controlled for unobserved confounding. The IV was defined using a measure of the hospital's risk-adjusted LOS for patients admitted for gastrointestinal hemorrhage.Principal Findings: The naive logit model predicted that a 1-day reduction in median postoperative LOS (ie, from a median of 6-5 d) lowered the 30-day readmission rate by 2 percentage points. The IV model predicted that a 1-day reduction in median postoperative LOS increased 30-day readmission rate by 3 percentage points.Conclusions: The findings indicate that a reduction in postoperative LOS is associated with an increased risk for 30-day readmission among Medicare patients undergoing bypass surgery, after both observed and unobserved confounding effects are corrected.

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