30-Day risk-standardized mortality and readmission rates after ischemic stroke in critical access hospitals

Abstract

Background and purpose: The critical access hospital (CAH) designation was established to provide rural residents with local access to emergency and inpatient care. CAHs, however, have poorer short-term outcomes for pneumonia, heart failure, and myocardial infarction compared with other hospitals. We assessed whether 30-day risk-standardized mortality rates (RSMRs) and risk-standardized readmission rates (RSRRs) after ischemic stroke differ between CAHs and non-CAHs.

Methods: The study included all fee-for-service Medicare beneficiaries 65 years of age or older with a primary discharge diagnosis of ischemic stroke (International Classification of Diseases, 9th revision codes 433, 434, 436) in 2006. Hierarchical generalized linear models calculated hospital-level RSMRs and RSRRs, adjusting for patient demographics, medical history, and comorbid conditions. Non-CAHs were categorized by hospital volume quartiles and the RSMR and RSRR posterior probabilities in comparison with CAHs were determined using linear regression with Markov chain Monte Carlo simulation.

Results: There were 10 267 ischemic stroke discharges from 1165 CAHs and 300 114 discharges from 3381 non-CAHs. The RSMRs of CAHs were higher than non-CAHs (11.9%± 1.4% vs 10.9%± 1.7%; P<0.001), but the RSRRs were comparable (13.7%± 0.6% vs 13.7%± 1.4%; P=0.3). The RSMRs for the 2 higher volume quartiles of non-CAHs were lower than CAHs (posterior probability of RSMRs higher than CAHs=0.007 for quartile 3; P<0.001 for quartile 4), but there were no differences for lower volume hospitals; RSRRs did not vary by annual hospital volume.

Conclusions: CAHs had higher RSMRs compared with non-CAHs, but readmission rates were similar. The observed differences may be partly explained by patient characteristics and annual hospital volume.

Figure 1. Distribution of Mean Medicare Payments per Hospitalization by Critical Access Hospital Status and Hospital Volume Quartiles

Box and whisker plots of mean Medicare payment per hospitalization in CAH and non-CAH volume categories. The upper boundaries of the boxes represent the seventy-fifth percentile, the lines bisecting the boxes represent the median or fiftieth percentile, and the lower boundaries of the boxes represent the twenty-fifth percentile. The lower and upper boundaries of the whiskers are set at the fifth and ninety-fifth percentiles, with dots representing hospitals beyond these percentiles. Mean (standard deviation) payments for CAHs and non-CAHs in order of increasing quartile are $5,021 (1,956), $6,129 (2,955), $6,691 (2,328), $7,180 (2,231), and $7,425 (1,928). Abbreviations: CAH, Critical Access Hospital.

Figure 2. Distribution of 30-Day All-Cause Risk-Standardized Mortality Rates and Readmission Rates by Critical Access Hospital (CAH) Status

Box and whisker plots of RSMR and RSRR by CAH status. The upper boundaries of the boxes represent the seventy-fifth percentile, the lines bisecting the boxes represent the median or fiftieth percentile, and the lower boundaries of the boxes represent the twenty-fifth percentile. The lower and upper boundaries of the whiskers are set at the fifth and ninety-fifth percentiles, with dots representing hospitals beyond these percentiles. Abbreviations: RSMR, risk-standardized mortality rate; RSRR, risk-standardized readmission rate; CAH, Critical Access Hospital.

Figure 3. Distribution of 30-Day All-Cause Risk-Standardized Mortality Rates and Readmission Rates by Critical Access Hospital Status and Hospital Volume Quartiles

Box and whisker plots of RSMR and RSRR by CAH and non-CAH status. The upper boundaries of the boxes represent the seventy-fifth percentile, the lines bisecting the boxes represent the median or fiftieth percentile, and the lower boundaries of the boxes represent the twenty-fifth percentile. The lower and upper boundaries of the whiskers are set at the fifth and ninety-fifth percentiles, with dots representing hospitals beyond these percentiles. Mean (standard deviation [SD]) RSMR values for CAHs and non-CAHs in order of increasing quartile are 11.9 (1.4), 11.5 (1.5), 11.3 (1.7), 11.2 (1.7), and 10.6 (1.6). Mean (SD) RSRR values are 13.7 (0.6), 13.8 (0.8), 13.8 (1.0), 13.8 (1.4), and 13.7 (1.6). Abbreviations: RSMR, risk-standardized mortality rate; RSRR, risk-standardized readmission rate; CAH, Critical Access Hospital.

Figure 4. Comparison of Risk-Standardized 30-Day All-Cause Mortality Rates and Readmission Rates Between Volume Quartiles of Non-Critical Access Hospitals (CAHs) and CAHs

Forest plot displays the posterior estimate for the comparison of RSMR/RSRR between volume quartiles of non-CAHs and all CAHs along with 95% posterior intervals. For example, the estimate of -1.03% comparing the 4^th (>75^th) quartile of non-CAH to CAH translated to approximately a 1% reduction in RSMR in non-CAHs in the highest quartile of case volume relative to CAHs. Posterior probabilities on the left indicate the probability that the estimate is greater than zero. Abbreviations: RSMR, risk-standardized mortality rate; RSRR, risk-standardized