A competing risk analysis for hospital length of stay in patients with burns

Abstract

Importance: Current outcome predictors for illness and injury are measured at a single time point-admission. However, patient prognosis often changes during hospitalization, limiting the usefulness of those predictions. Accurate depiction of the dynamic interaction between competing events during hospitalization may enable real-time outcome assessment.

Objective: To determine how the effects of burn outcome predictors (ie, age, total body surface area burn, and inhalation injury) and the outcomes of interest (ie, mortality and length of stay) vary as a function of time throughout hospitalization.

Design, setting, and participants: In this retrospective study, we used the American Burn Association's National Burn Repository, containing outcomes and patient and injury characteristics, to identify 95 579 patients admitted with an acute burn injury to 80 tertiary American Burn Association burn centers from 2000 through 2009. We applied competing risk statistical methods to analyze patient outcomes.

Main outcomes and measures: We estimated the cause-specific hazard rates for death and discharge to assess how the instantaneous risk of these events changed across time. We further evaluated the varying effects of patient age, total body surface area burn, and inhalation injury on the probability of discharge and death across time.

Results: Maximum length of stay among patients who died was 270 days and 731 days among those discharged. Total body surface area, age, and inhalation injury had significant effects on the subdistribution hazard for discharge (P < .001); these effects varied across time (P < .002). Burn size (coefficient -0.046) determined early outcomes, while age (coefficient -0.034) determined outcomes later in the hospitalization. Inhalation injury (coefficient -0.622) played a variable role in survival and hospital length of stay.

Conclusions and relevance: Real-time measurement of dynamic interrelationships among burn outcome predictors using competing risk analysis demonstrated that the key factors influencing outcomes differed throughout hospitalization. Further application of this analytic technique to other injury or illness types may improve assessment of outcomes.

Figure 1. Thirty-Day Discharge and Death Rates for Patients With Burn Injury

A, Cumulative incidence functions for death after admission. Dashed vertical lines mark 1 and 2 weeks. B, Proportion of deaths and discharges for the first 30 days after admission. C, Smoothed cause-specific hazard rates for discharge. D, Smoothed cause-specific hazard rates for death.

Figure 2. Effects of Burn Size, Age, and Inhalation Injury Across Time

Estimated constant and time-varying coefficients for the effect on the subdistribution hazard of discharge with death as a competing risk. Black solid and dotted lines show pointwise 95% confidence limits and 95% confidence bands, respectively. A, Burn size. B, Age. C, Inhalation injury.