Rationale: The United States has seven times as many intensive care unit (ICU) beds per capita as the United Kingdom; the effect on care of critically ill patients is unknown.
Objectives: To compare medical ICU admissions in the United States and United Kingdom.
Methods: Retrospective (2002-2004) cohort study of 172,785 ICU admissions (137 United States ICUs, Project IMPACT database; 160 United Kingdom ICUs, Case Mix Program) with patients followed until initial hospital discharge.
Measurement and main results: United Kingdom (vs. United States) admissions were less likely to be admitted directly from the emergency room (ER) (33.4% vs. 58%); had longer hospital stays before ICU admission (mean days 2.6 ± 8.2 vs. 1 ± 3.6); and fewer were greater than or equal to 85 years (3.2% vs. 7.8%). United Kingdom patients were more frequently mechanically ventilated within 24 hours after ICU admission (68% vs. 27.4%); were sicker (mean Acute Physiology Score 16.7 ± 7.6 vs. 10.6 ± 6.8); and had higher primary hospital mortality (38% vs. 15.9%; adjusted odds ratio, 1.73; 95% confidence interval, 1.50-1.99). There was no mortality difference for mechanically ventilated patients admitted from the ER (adjusted odds ratio, 1.09; 95% confidence interval, 0.89-1.33). Comparisons of hospital mortality were confounded by differences in case mix; hospital length of stay (United Kingdom median 10 d [interquartile range {IQR}, 3-24] vs. United States 6 d [IQR, 3-11]; and discharge practices (more United States patients were discharged to skilled care facilities [29% of survivors vs. 6% in the United Kingdom]).
Conclusions: Lower United Kingdom ICU bed availability is associated with fewer direct admissions from the ER, longer hospital stays before ICU admission, and higher severity of illness. Interpretation of between-country hospital outcomes is confounded by differences in case mix, processes of care, and discharge practices.