Associations of Intensive Care Unit Capacity Strain with Disposition and Outcomes of Patients with Sepsis Presenting to the Emergency Department

Abstract

Rationale: Intensive care unit (ICU) capacity strain refers to the potential limits placed on an ICU's ability to provide high-quality care for all patients who may need it at a given time. Few studies have investigated how fluctuations in ICU capacity strain might influence care outside the ICU.

Objectives: To determine whether ICU capacity strain is associated with initial level of inpatient care and outcomes for emergency department (ED) patients hospitalized for sepsis.

Methods: We performed a retrospective cohort study of patients with sepsis admitted from the ED to a medical ward or ICU at three hospitals within the University of Pennsylvania Health System between 2012 and 2015. Patients were excluded if they required life support therapies, defined as invasive or noninvasive ventilatory support or vasopressors, at the time of admission. The exposures were four measures of ICU capacity strain at the time of the ED disposition decision: ICU occupancy, ICU turnover, ICU census acuity, and ward occupancy. The primary outcome was the decision to admit to a ward or to an ICU. Secondary analyses assessed the association of ICU capacity strain with in-hospital outcomes, including mortality.

Results: Among 77,142 hospital admissions from the ED, 3,067 patients met the study's eligibility criteria. The ICU capacity strain metrics varied between and within study hospitals over time. In unadjusted analyses, ICU occupancy, ICU turnover, ICU census acuity, and ward occupancy were all negatively associated with ICU admission. In the fully adjusted model including patient-level covariates, only ICU occupancy remained associated with ICU admission (odds ratio, 0.87; 95% confidence interval, 0.79-0.96; P = 0.005), such that a 10% increase in ICU occupancy (e.g., one additional patient in a 10-bed ICU) was associated with a 13% decrease in the odds of ICU admission. Among the subset of patients admitted initially from the ED to a medical ward, ICU occupancy at the time of admission was associated with increased odds of hospital mortality (odds ratio, 1.61; 95% confidence interval, 1.21-2.14; P = 0.001).

Conclusions: The odds that patients in the ED with sepsis who do not require life support therapies will be admitted to the ICU are reduced when those ICUs experience high occupancy but not high levels of other previously explored measures of capacity strain. Patients with sepsis admitted to the wards during times of high ICU occupancy had increased odds of hospital mortality.

Keywords: ICU occupancy; intensive care unit capacity strain; sepsis.

Figure 1.

Intensive care unit (ICU) capacity strain metric variability, by hospital. The degree of ICU capacity strain metrics (vertical axes) is plotted on an hourly (for ICU occupancy, ICU turnover, and ward occupancy) or daily (for ICU census acuity) basis for the three study hospitals, represented by different colors, over a representative 3-month period during the study period. The figure demonstrates that the ICU capacity strain metrics varied on a granular level, both within and among study hospitals, over the duration of the study period. SOFA = Sequential (Sepsis-related) Organ Failure Assessment.

Figure 2.

Locally weighted scatterplot smoothing plots of the percent intensive care unit (ICU) occupancy and open ICU beds against ICU admission. Among patients presenting to the emergency department with sepsis who do not receive life support therapies, the likelihood of ICU (vs. ward) admission (vertical axis) is plotted against ICU occupancy, represented as (A) percent ICU occupancy and (B) the number of open ICU beds, with a full ICU represented on the leftmost point on each horizontal axis. The figure demonstrates that beginning at approximately 70% occupancy and five open ICU beds, increasing ICU occupancy at time of the emergency department disposition decision is linearly associated with a reduced likelihood of ICU admission. (The plots were restricted to ICU occupancy ≥56.25% accounting for 95% of the study population and ≤10 open ICU beds accounting for 99% of the study population.)

Figure 3.

Association of intensive care unit (ICU) occupancy and hospital mortality among patients with sepsis admitted to the ward. Among patients presenting to the emergency department with sepsis who do not receive life support therapies and are admitted initially to a medical ward, observed hospital mortality (vertical axis) is plotted against the ICU occupancy (in 5% bucketed increments) at the time of the emergency department disposition decision. The figure demonstrates that ICU occupancy (between 50% and 100%) appears linearly associated with increased hospital mortality.