The Association of ICU Acuity With Outcomes of Patients at Low Risk of Dying

Vranas, Kelly C. MD1,2; Jopling, Jeffrey K. MD, MSHS1,3; Scott, Jennifer Y. MS1; Badawi, Omar PharmD, MPH4,5,6; Harhay, Michael O. PhD7,8; Slatore, Christopher G. MD, MS2,9; Ramsey, Meghan C. MD1,10; Breslow, Michael J. MD4; Milstein, Arnold S. MD, MPH1; Kerlin, Meeta Prasad MD, MSCE11

Objective: Many ICU patients do not require critical care interventions. Whether aggressive care environments increase risks to low-acuity patients is unknown. We evaluated whether ICU acuity was associated with outcomes of low mortality-risk patients. We hypothesized that admission to high-acuity ICUs would be associated with worse outcomes. This hypothesis was based on two possibilities: 1) high-acuity ICUs may have a culture of aggressive therapy that could lead to potentially avoidable complications and 2) high-acuity ICUs may focus attention toward the many sicker patients and away from the fewer low-risk patients.

Design: Retrospective cohort study.

Setting: Three hundred twenty-two ICUs in 199 hospitals in the Philips eICU database between 2010 and 2015.

Patients: Adult ICU patients at low risk of dying, defined as an Acute Physiology and Chronic Health Evaluation-IVa–predicted mortality of 3% or less.

Exposure: ICU acuity, defined as the mean Acute Physiology and Chronic Health Evaluation IVa score of all admitted patients in a calendar year, stratified into quartiles.

Measurements and Main Results: We used generalized estimating equations to test whether ICU acuity is independently associated with a primary outcome of ICU length of stay and secondary outcomes of hospital length of stay, hospital mortality, and discharge destination. The study included 381,997 low-risk patients. Mean ICU and hospital length of stay were 1.8 ± 2.1 and 5.2 ± 5.0 days, respectively. Mean Acute Physiology and Chronic Health Evaluation IVa–predicted hospital mortality was 1.6% ± 0.8%; actual hospital mortality was 0.7%. In adjusted analyses, admission to low-acuity ICUs was associated with worse outcomes compared with higher-acuity ICUs. Specifically, compared with the highest-acuity quartile, ICU length of stay in low-acuity ICUs was increased by 0.24 days; in medium-acuity ICUs by 0.16 days; and in high-acuity ICUs by 0.09 days (all p < 0.001). Similar patterns existed for hospital length of stay. Patients in lower-acuity ICUs had significantly higher hospital mortality (odds ratio, 1.28 [95% CI, 1.10–1.49] for low-; 1.24 [95% CI, 1.07–1.42] for medium-, and 1.14 [95% CI, 0.99–1.31] for high-acuity ICUs) and lower likelihood of discharge home (odds ratio, 0.86 [95% CI, 0.82–0.90] for low-, 0.88 [95% CI, 0.85–0.92] for medium-, and 0.95 [95% CI, 0.92–0.99] for high-acuity ICUs).

Conclusions: Admission to high-acuity ICUs is associated with better outcomes among low mortality-risk patients. Future research should aim to understand factors that confer benefit to patients with different risk profiles.