Patterns of Admission to the ICU in the VA Health System

The costs of critical care in the United States account for nearly 1% of the gross domestic product and nearly 15% of all hospital costs. There are wide variations in the use of critical care resources and, according to researchers, “better triage decisions on admissions, that is, choices about the first hospital unit to which a patients is admitted, could aid in efforts to improve the quality and decrease the cost of acute inpatient care.”

There have been studies to examine the characteristics of patients referred to the intensive care unit (ICU) as well as the severity of illness of patients once admitted to the ICU. However, there are no data on the proportion of all medical patients presenting for hospital admission that are sent to the ICU or how this proportion varies across all levels of patient severity.

Researchers recently conducted a retrospective cohort study of the initial nonsurgical admission of 289,310 patients admitted from the emergency department (ED) or outpatient clinic to 118 acute care hospitals in the Veterans Affairs healthcare system between July 1, 2009, and June 30, 2010. The analysis was designed to answer 3 questions: (1) what is the 30-day predicted mortality rate (severity) of medical patients admitted directly to the ICU from the ED or outpatient clinic? (2) how much does direct admission to the ICU vary between hospitals for patients with the same 30-day predicted mortality rate?, and (3) are comparisons of hospital admitting patterns dependent on patient severity?

The primary outcome measure was direct admission to the ICU. Severity (30-day predicted mortality rate) was measured using a modified Veterans Affairs ICU score based on laboratory data and comorbidities around admission. Results of the analysis were reported in Archives of Internal Medicine [2012;172(16):1220-1226].

Of the 289,310 patients admitted to 1 of 118 hospitals in 48 states during the study period, 10.9% (n=31,555) were admitted directly to the ICU. Patients admitted directly to the ICU had higher mean predicted 30-day mortality rates compared with patients admitted to the non-ICU ward (7.5% vs 3.5%). Both populations had a relatively low predicted mortality rate at admission.

There was wide variation among the 118 hospitals in the proportion of patients admitted to the ICU. After adjusting for predicted mortality and diagnosis on admission, rates of admission to the ICU ranged from 1.6% to 29.5% (median ICU admission rate, 6.9%) for patients with median predicted mortality.

Of the patients admitted to the ICU, 53.2% (n=16,780) had a 30-day predicted mortality at admission of ≤2%. Among this low-risk group, there was wide variation in the rate of admission to the ICU, ranging from 1.2% to 38.9% (median, 7.3%).

For a 1-standard deviation increase in severity, the adjusted odds of admission to the ICU varied substantially across hospitals. As a result, 66.1% of hospitals were in different quartiles of ICU use for low- versus high-risk patients.

After adjusting for severity at admission, patients admitted to the ICU had higher odds of death at 30 days but not at 90 days. However, when the treatment effect was estimated as a function of severity at admission, admission to the ICU was protective against death at 30 days for patients with expected mortality >18.4% at admission and protective against death at 90 days for patients with expected mortality >8.8%.

Limitations to the study cited by the authors included a lack of information about patient preference and data on vital signs at admission. The data set also did not provide physician-level characteristics. Finally, because the data were representative of a single healthcare system, the researchers cautioned that the results may not be generalizable to other health systems.

In summary, the researchers said, “We found that many high-risk patients were not directly admitted to the ICU, but that approximately half of all medical patients directly admitted to the ICU were at low risk.” They added, “the proportion of low- and high-risk patients admitted to the ICU, variation in ICU admitting patterns among hospitals, and the sensitivity of hospital rankings to patient risk all likely reflect a lack of consensus about which patients most benefit from ICU admission.”