The differential associations of preexisting conditions with trauma-related outcomes in the presence of competing risks

Introduction: Pre-existing chronic conditions (PECs) pose a unique problem for the care of aging trauma populations. However, the relationships between specific conditions and outcomes after injury are relatively unknown. Evaluation of trauma patients is further complicated by their discharge to care facilities, where mortality risk remains high. Traditional approaches for evaluating in-hospital mortality do not account for the discharge of at-risk patients, which constitutes a competing risk event to death. The objective of this study was to evaluate associations between 40 PECs and two clinical outcomes in the context of competing risks among older trauma patients. Methods: This retrospective study evaluated blunt-injured patients aged 55 years and older admitted to a level I trauma centre in 2006-2012. Outcomes were hospital length of stay (HLOS) and in-hospital mortality. Survivors were classified as discharges home or discharges to care facilities. Competing risks regression was used to evaluate each PEC with in-hospital mortality, accounting for discharges to care facilities as competing events. Competing risk estimates were compared to Cox model estimates, for which all survivors to discharge were non-events. Analyses were stratified using injury-based mortality risk at a 50% cutpoint (high versus low). Results: Among 4653 patients, 176 died in-hospital, 3059 were discharged home, and 1418 were discharged to a care facility. Most patients (98%) were classified with a low mortality risk. Only haemophilia and coagulopathy were consistently associated with longer HLOS. In the low-risk subgroup, in-hospital mortality was most strongly associated with liver diseases, haemophilia, and coagulopathy. In the high-risk group, Parkinson's disease, depression, and cancers showed the strongest associations. Accounting for the competing event altered estimates for 12 of 19 significant conditions. Conclusions: Excess mortality among patients expected to survive their injuries may be attributable to complications resulting from PECs. Discharges to care facilities constitute a bias in the evaluation of in-hospital mortality and should be considered for the accurate calculation of risk. In conjunction with injury measures, consideration of PECs provides physicians with a foundation to plan clinical decisions in older trauma patients. (C) 2015 Elsevier Ltd. All rights reserved.