Risk of Death Influences Regional Variation in Intensive Care Unit Admission Rates among the Elderly in the United States

Rationale The extent to which geographic variability in ICU admission across the United States is driven by patients with lower risk of death is unknown. Objectives To determine whether patients at low to moderate risk of death contribute to geographic variation in ICU admission. Methods Retrospective cohort of hospitalizations among Medicare beneficiaries (age > 64 years) admitted for ten common medical and surgical diagnoses (2004 to 2009). We examined population-adjusted rates of ICU admission per 100 hospitalizations in 304 health referral regions (HRR), and estimated the relative risk of ICU admission across strata of regional ICU and risk of death, adjusted for patient and regional characteristics. Measurement and Main Results ICU admission rates varied nearly two-fold across HRR quartiles (quartile 1 to 4: 13.6, 17.3, 20.0, and 25.2 per 100 hospitalizations, respectively). Observed mortality for patients in regions (quartile 4) with the greatest ICU use was 17% compared to 21% in regions with lowest ICU use (quartile 1) (p<0.001). After adjusting for patient and regional characteristics, including regional differences in ICU, skilled nursing, and long-term acute care bed capacity, individuals’ risk of death modified the relationship between regional ICU use and an individual’s risk of ICU admission (p for interaction<0.001). Region was least important in predicting ICU admission among patients with high (quartile 4) risk of death (RR 1.27, 95% CI 1.22–1.31, for high versus low ICU use regions), and most important for patients with moderate (quartile 2; RR 1.63, 95% CI 1.53–1.72, quartile 3; RR 1.56 95% CI 1.47–1.65) and low (quartile 1) risk of death (RR 1.50, 95% CI 1.41–1.59). Conclusions There is wide variation in in ICU use by geography, independent of ICU beds and physician supply, for patients with low and moderate risks of death.