Medicare Accountable Care Organizations and Inpatient Mortality Rates

Studies have linked Accountable Care Organizations (ACOs) to improved primary care, but there is little research on how ACOs affect care in other settings. We examined whether Medicare ACOs have improved hospital quality of care, specifically focusing on preventable inpatient mortality, including measures on which ACO hospitals are not explicitly held accountable. We used 2008–2014 Agency for Healthcare Research and Quality Healthcare Cost and Utilization Project (HCUP) State Inpatient Databases (SID) hospital discharge data from 34 states’ Medicare ACO and non-ACO hospitals in conjunction with data from the American Hospital Association (AHA) Annual Survey and Survey of Care Systems and Payment. The HCUP SID comprise the largest collection of all-payer, discharge-level hospital care in the United States, while the AHA data contain hospital attributes, including information about ACO affiliation. We estimated discharge-level logistic regression models that measured the relationship between ACO affiliation and mortality following admissions for acute myocardial infarction, abdominal aortic aneurysm (AAA) repair, coronary artery bypass grafting, and pneumonia, controlling for patient demographic mix, hospital and year fixed effects, and pre-existing time trend differentials between ACO hospitals and non-ACO hospitals. Our sample included between 11,547 discharges for AAA repair in 2010 and 232,637 discharges for pneumonia in 2008, with counts varying by Inpatient Quality Indicator (IQI) and year. Our results suggest that avoidable deaths for the studied conditions decreased on average for hospitals that joined Medicare ACOs, with the magnitude of improvement growing over time as hospitals gained experience with ACO models. For AAA repair, ACOs were associated with reductions in the odds of mortality by factors of 0.47 (p=0.08) to 0.15 (p=0.02) to 0.03 (p=0.01) to 0.01 (p=0.01) over 2011–2014. Stratifying results by ACO leadership revealed that the magnitudes of improvement were larger for ACOs led by the hospital or jointly led by hospital and physician groups than for ACOs without any hospital leadership. Not all results achieved statistical significance, which may reflect heterogeneity in ACO implementation; however, the pattern of results with respect to average adjusted ACO effects held across all conditions. Stakeholders should consider these peripheral benefits of ACO participation when assessing their overall performance.