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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

doi: 10.1097/CCM.0000000000002798
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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.

1Clinical Excellence Research Center, Department of Medicine, Stanford University, Stanford, CA.

2Division of Pulmonary and Critical Care, Department of Medicine, Oregon Health & Science University, Portland, OR.

3Department of Surgery, Stanford University, Stanford, CA.

4Department of Research and Development, Philips Healthcare, Baltimore, MD.

5Department of Pharmacy Practice and Science, University of Maryland School of Pharmacy, Baltimore, MD.

6Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA.

7Department of Biostatistics, Epidemiology and Informatics, University of Pennsylvania, Philadelphia, PA.

8Center for Health Equity Research and Promotion, Corporal Michael J. Crescenz VA Medical Center, Philadelphia, PA.

9Health Services Research & Development, VA Portland Health Care System, Portland, OR.

10Division of Pulmonary and Critical Care, Department of Medicine, Stanford University, Stanford, CA.

11Pulmonary, Allergy and Critical Care Division, Department of Medicine, University of Pennsylvania, Philadelphia, PA.

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Drs. Vranas, Jopling, Ramsey, Badawi, Harhay, Slatore, and Kerlin contributed to the conception and design of this study. Drs. Badawi, Breslow, and Milstein contributed to data acquisition. Ms. Scott and Dr. Harhay contributed to the analysis of data. Dr. Vranas, Ms. Scott, and Drs. Badawi, Harhay, Slatore, and Kerlin contributed to interpretation of data. All authors have made substantial contributions to the conception and design, acquisition of data, or analysis and interpretation of data; have contributed to drafting the article for important intellectual content; and have provided final approval of the version to be published.

Dr. Vranas was supported by T32 HL083808 07 and the Medical Research Foundation. Drs. Vranas and Kerlin received support for article research from the National Institutes of Health. Dr. Jopling was supported by National Institutes of Health UL1 TR001085. Ms. Scott received funding from Medical Research Foundation, and disclosed work for hire. Dr. Harhay was supported by resources from the Corporal Michael J. Crescenz VA Medical Center, Philadelphia, PA. Dr. Badawi received funding from Philips Healthcare and ICMed. Dr. Slatore was supported by resources from the VA Portland Health Care System, Portland, OR and disclosed government work. Dr. Ramsey received funding from Intuitive Surgical and ProLung. Dr. Breslow received funding from Philips. Dr. Milstein disclosed that Philips electronics provided access to its database. The remaining authors have disclosed that they do not have any potential conflicts of interest.

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The Department of Veterans Affairs did not have a role in the conduct of the study; in the collection, management, analysis, or interpretation of data; or in the preparation of the article. The views expressed in this article are those of the authors and do not necessarily represent the views of the Department of Veterans Affairs or the U.S. Government.

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