Abstract 255: Association Of Hospital Market Area Dominance With Out-of-hospital Cardiac Arrest Survival To Admission

Abstract

Introduction: Access to care has been measured by geographic distance, transport time or provider density. For emergency care sensitive conditions, like out-of-hospital cardiac arrest (OHCA), market area coverage may be associated with short-term outcomes due to the need for access to definitive care. Our objective was to evaluate the association of market area dominance with survival to hospital admission. Methods: ED-treated OHCA were identified in age-eligible Medicare fee-for service claims using ICD 9/10 codes and ED charges. Hospital market shares were defined as the cumulative proportion of all OHCA claims treated at the hospital of interest within a group of ZIP code tabulation areas (ZCTAs) centered around the hospital. Market share was calculated using sequential addition of ZCTAs. Hospital Market Areas (HMAs) included all ZCTAs where the cumulative market share exceeded a threshold (<50% 50-74% 75-89% ≥90%). Survival to admission was determined using in-patient claims and vital status data. The primary predictor, maximum HMA threshold, is the highest market share proportion covering that ZCTA. A ZCTA with a 90% max HMA has one hospital treating 90% of OHCA case in that ZCTA or closer. Relative risk of survival was calculated using modified Poisson regression with hospital random effect and patient characteristics (age, sex, race, comorbidity). Results: Of the 194,914 claims treated at 4,436 hospitals between 2013 and 2015, 45% were female, 16% Black, 77% White, and 50% from large metro areas. 28% of claims were from a ZCTA with <50% max HMA (an area where no single hospital treats the majority of OHCA). Relative risk of survival to admission decreased as the max HMA increased [RR[95%CI] 50-74%: 0.97[0.95, 0.99]; 75-89%: 0.94 [0.91, 0.98]; ≥90%: 0.90 [0.83, 0.98]. Small and non-metro areas were associated with lower survival likelihood. Interactions were not significant between max HMA and small metro areas; non-metro areas saw a greater reduction in survival likelihood for ZCTAs with max HMAs >75%. Conclusion: For OHCA, market dominance was associated with lower likelihood of survival to hospital admission. The likelihood of survival decreased as market dominance increased. Further study is needed to develop strategies to mitigate this disparity.