Dr Joseph S Ross and colleagues at the Mount Sinai School of Medicine, New York, analysed cross-sectional data from Medicare claims for all fee-for-service beneficiaries admitted to acute care hospitals for these three common conditions between 2004 and 2006. ‘Using hierarchical logistic-regression models for each condition, we estimated the change in the odds of death within 30 days associated with an increase of 100 patients in the annual hospital volume.’
Pneumonia patients treated at larger-volume hospitals were 5% less likely to die in the first month than patients treated at hospitals where few cases were handled. The death rate for heart failure was 9% lower for busy hospitals and 11% lower for heart attacks. Generally, teaching hospitals needed fewer patients to attain a lower risk of death.
For each of the three conditions, the association between volume and outcome was reduced as the hospital's volume increased. For acute myocardial infarction, once the annual volume reached 610 patients (95% confidence interval [CI], 539 to 679), an increase in the hospital volume by 100 patients was no longer significantly associated with reduced odds of death. The volume threshold was 500 patients (95% CI, 433 to 566) for heart failure and 210 patients (95% CI, 142 to 284) for pneumonia.
Understandably, patients who receive surgery, or other procedures, fare better if treated by more experienced doctors. The Mount Sinai study is the first to look at outcomes for common medical conditions. The researchers calculated, for example, that in a hospital that only treated 17 heart attacks each year, its 30-day death rate could drop by 20% if the hospital treated an additional 100 heart attack patients annually. If it had 70 cases a year to begin with, adding 100 more would result in a 10% reduction.
Adding 100 cases to a hospital that already treats 236 heart attacks would cut the death rate by just 4%. The threshold of improvement was reached once the annual volume hit 610.
Generally, hospitals that had treated the fewest patients with those conditions were the most risky -- and hospital size made no difference.