Characteristics and Outcomes for Low-Risk Hospital Admissions Admitted to the ICU: A Multisite Cohort Study

IMPORTANCE: Prognostication following ICU admission can often be determined based on known risk factors, including demographics and illness severity; however, little is known about outcomes of patients deemed to be "low-risk" at the time of hospital admission who subsequently are admitted to the ICU. OBJECTIVES: The objectives of this study were to determine the characteristics, outcomes, and costs for patients requiring ICU admission despite having lower predicted mortality when they were admitted to the hospital. DESIGN, SETTING, AND PARTICIPANTS: In this historical cohort study, we used a prospectively maintained ICU registry that included all ICU admissions to The Ottawa Hospital for patients 18 years or older from January 2011 to December 2016. We classified patients as low-risk using the Hospital-patient 1-year Mortality Risk at admission score, a hospital admission score validated to predict 1-year mortality. MAIN OUTCOMES AND MEASURES: The primary outcome was inhospital mortality. Secondary outcomes included adverse events, resource utilization, and costs. RESULTS: Of the 17,173 total ICU patients, 3,445 (20.1%) were classified as low-risk at hospital admission. Low-risk patients were younger (48.7 vs 67.5 yr; p < 0.001) and had a lower Multiple Organ Dysfunction Score (2.37 vs 4.14; p < 0.001). Mortality for low-risk patients was significantly lower than for non-low-risk patients (4.1% vs 25.4%; p < 0.001). For low-risk patients, multivariable logistic regression showed mortality was independently associated with older age (odds ratio, 1.02 per 1 yr; 95% CI, 1.00-1.03 per 1 yr), Multiple Organ Dysfunction Score (odds ratio, 1.42 per 1 point; 95% CI, 1.31-1.54 per 1 point), fluid management adverse events (odds ratio, 2.84; 95% CI, 1.29-6.25), hospital-acquired infections (odds ratio, 1.60; 95% CI, 1.02-2.51), and mechanical ventilation (odds ratio, 1.98; 95% CI, 1.20-3.26). CONCLUSIONS AND RELEVANCE: Despite their robust premorbid status, low-risk patients admitted to the ICU had significant inhospital mortality. Fluid management adverse events, hospital-associated infections, multiple organ dysfunction, and mechanical ventilation are important prognostic factors for low-risk patients.