Impact of Patient Volume on the Mortality Rate of Adult Intensive Care Unit Patients

OBJECTIVE: Expert task forces have proposed that adult critical care medicine services should be regionalized in order to improve outcomes. However, it is currently unknown if high intensive care unit (ICU) patient volumes are associated with reduced mortality rate. The objective was to investigate whether high-volume ICUs have better mortality outcomes than low-volume ICUs. DESIGN: Retrospective cohort study analyzing the association between ICU volume and in-hospital mortality using Project IMPACT (a clinical outcomes database created by the Society of Critical Care Medicine). PATIENTS: The analyses were based on 70,757 patients admitted to 92 ICUs between 2001 and 2003. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The main outcome measure was in-hospital mortality. Hierarchical logistic regression modeling was used to examine the volume-outcome association. The median (interquartile range) ICU volume was 827 (631-1,234) patient admissions per year. The overall mortality rate was 14.6%. After controlling for patient risk factors and ICU characteristics, and clustering, there was evidence that patients admitted to high-volume ICUs had improved outcomes (p = .025). However, this mortality benefit was seen only in high-risk patients treated at ICUs treating high volumes of high-risk patients. CONCLUSIONS: There is evidence that high ICU patient volumes are associated with lower mortality rates in high-risk critically ill adults.