Objectives: Recent evidence suggests a measurable reduction in mortality for patients transferred from a nontertiary trauma center (Level III or IV) to a Level I trauma center, but not for those transferred to a Level II trauma center. Whether this can be generalized to a predominantly rural region with fewer tertiary trauma care resources is uncertain. This study sought to evaluate mortality differences for patients initially presenting to nontertiary trauma centers in a predominantly rural region depending on transfer status.Methods: This was a retrospective cohort study of patients initially presenting to 104 nontertiary trauma centers in Oklahoma and meeting the state's criteria for major trauma. Patients dying within 1 hour of emergency department (ED) arrival at the nontertiary trauma center were excluded. The exposure variable of interest was admission status, which was categorized as either transfer to a tertiary (Level I or II) trauma center within 24 hours or admission to a nontertiary trauma center. Propensity scores were used to minimize the selection bias inherent in the decision to admit or transfer a patient for higher-level care. Multiple logistic regression was used to generate three propensity score models: probability of transfer to either a Level I or II, Level I only, and Level II only. Propensity scores were then included as a covariate in multivariable Cox regression models assessing outcome differences between admitted and transferred patients. The outcome of interest was 30-day mortality, defined as death at either the nontertiary trauma center or the tertiary trauma center within 30 days of arrival at the initial Level III ⁄ IV center's ED.Results: A total of 6,229 patients met study criteria, of whom 2,669 (43%) were transferred to tertiary trauma centers. Of those transferred, 1,422 patients (53%) were transferred to a Level I trauma center. Crude mortality was lower for patients transferred to tertiary trauma centers compared to those remaining at nontertiary trauma facilities (hazard ratio [HR] = 0.59; 95% confidence interval [CI] = 0.48 to 0.72). After adjusting for the propensity to be transferred, Injury Severity Score (ISS), presence of severe head injury, and age, transfer to a tertiary trauma center was associated with a significantly lower 30-day mortality (HR = 0.38; 95% CI = 0.30 to 0.50) compared to admission and treatment at a nontertiary trauma center. The observed survival benefit was similar for patients transferred to a Level I trauma center (HR = 0.36; 95% CI = 0.20 to 0.4) and those transferred to a Level II center (HR = 0.45; 95% CI = 0.33 to 0.61).Conclusions: This study suggests a survival benefit among patients initially presenting to nontertiary trauma centers who are subsequently transferred to tertiary trauma centers compared to those remaining in nontertiary trauma centers, even after adjusting for variables affecting the likelihood of transfer. Although this survival benefit was larger for patients treated at a Level I trauma center, Level II trauma...

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