The effect of pre-existing medical conditions and age on mortality after injury

Background. Pre-existing medical conditions (PMCs) have been shown to increase mortality after trauma even after adjustment for the effect of chronological aging. It has been suggested that there is an interaction between injury severity and physiologic reserve, such that diminished physiologic reserve will have an adverse effect on survival at lower injury severity, but that at higher levels of injury severity, physiologic reserve will have much less of an impact. Methods. Records of 65,743 patients, admitted after trauma, were extracted from the database of the United Kingdom Trauma Network to explore the impacts of age, gender and PMCs on mortality, and modification of these effects by severity of injury. Results. PMCs were categorized as absent (23%), present (23%), or unrecorded (54%). There was an increase in mortality with increasing age at all levels of injury severity. Presence of a PMC was associated with a marked increase in mortality of patients with minor injuries (odds ratio [OR] = 5.9, 95% confidence interval [CI] 4.4, 8.0) or moderate injuries (OR = 2.0, 95% CI 1.4, 2.9), but not in those with more severe injuries (OR = 1.1, 95% CI 0.9, 1.4). The impact of age and male gender were also somewhat more pronounced for patients with less severe injuries. Conclusion. These findings support the hypothesis of an interaction between physiologic reserve and injury severity, where PMCs are associated with increased mortality when combined with low to moderate severity injuries, but not when combined with more severe injuries.