Higher ICU Capacity Strain Is Associated With Increased Acute Mortality in Closed ICUs.

OBJECTIVES: To determine whether patients admitted to an ICU during times of strain, when compared with its own norm (i.e. accommodating a greater number of patients, higher acuity of illness, or frequent turnover), is associated with a higher risk of death in ICUs with closed models of intensivist staffing.

DESIGN: We conducted a large, multicenter, observational cohort study. Multilevel mixed effects logistic regression was used to examine relationships for three measures of ICU strain (bed census, severity-weighted bed census, and activity-weighted bed census) on the day of admission with risk-adjusted acute hospital mortality.

SETTING: Pooled case mix and outcome database of adult general ICUs participating in the Intensive Care National Audit and Research Centre Case Mix Programme.

MEASUREMENTS AND MAIN RESULTS: The analysis included 149,310 patients admitted to 215 adult general ICUs in 213 hospitals in United Kingdom, Wales, and Northern Ireland. A relative lower strain in ICU capacity as measured by bed census on the calendar day (daytime hours) of admission was associated with decreased risk-adjusted acute hospital mortality (odds ratio, 0.94; 95% CI, 0.90-0.99; p = 0.01), whereas a nonsignificant association was seen between higher strain and increased acute hospital mortality (odds ratio, 1.04; 95% CI, 1.00-1.10; p = 0.07). The relationship between periods of high ICU strain and acute hospital mortality was strongest when bed census was composed of higher acuity patients (odds ratio, 1.05; 95% CI, 1.01-1.10; p = 0.03). No relationship was seen between high strain and ICU mortality.

CONCLUSIONS: In closed staffing models of care, variations in bed census within individual ICUs was associated with patient's predicted risk of acute hospital mortality, particularly when its standardized bed census consisted of sicker patients.