What's new in emergencies, trauma, and shock? Correlating rapid prehospital transport and survival.

The end goal of the development of trauma systems and the regionalization of trauma care is improved patient outcomes. The two basic structural components needed are the availability of trauma centers that meet the need of trauma patients and the presence of a highly coordinated emergency medical services (EMS) system that properly triages injured patients to appropriate destinations. Several large studies have demonstrated improved outcomes with rapid evacuation of severely injured patients to a trauma center.[1-3] In a model developed by the 2007 US Metropolitan Municipalities’ EMS Medical Directors’ Consortium defining evidence-based performance measures for emergency medical services, the number needed to treat (NNT) for trauma patients of all age groups with injury severity score (ISS) of 15 or greater was estimated to be 11 with direct transport to a trauma center.[4] One death is prevented for every 11 severely injured trauma patients if transported directly to a trauma center in an urban or large suburban EMS system. The impact of direct transport to a trauma center on survival is even greater for sicker and older patients with an estimated NNT of 3 for patients who are over 65 years of age with an ISS higher than 21.[4]

Additionally, prehospital or field triage decision schemes help EMS providers identify and rapidly transport severely injured patients to an appropriate trauma center. The Guidelines for Field Triage of Injured Patients developed by the Center for Disease Control and Prevention (CDC) in collaboration with the American College of Surgeons Committee on Trauma (ACS-COT) are the most widely adopted by EMS systems in the US.[5] Despite the comprehensive nature of these decision schemes, outcome research focusing on identifying specific categories of trauma patients who would benefit from faster prehospital interventions and more rapid transport is needed to evaluate the performance of highly advanced urban EMS systems and to help optimize their triage and transport processes.

In this issue of Journal of Emergencies, Trauma and Shock, the authors of the article “Pre-Hospital Transport Times and Survival for Hypotensive Patients with Penetrating Thoracic Trauma” examine the association between prehospital time intervals and mortality as a primary trauma outcome. They conduct a retrospective cohort study analyzing data from a state trauma registry and limit their study population to a specific category of trauma patients; those with penetrating thoracic trauma in an urban setting. The study finds that mortality rates increase with prolonged total prehospital time intervals for patients with penetrating thoracic trauma who are hypotensive with a systolic blood pressure (SBP) less than 90 mmHg (measured in emergency department) and with ISS equal or greater than 16. The study also finds that “more severely injured patients arrive at urban trauma centers sooner.” The authors conclude that “mortality is strongly predicted by injury severity, although shorter transport time improves survival” and find that “careful planning to optimize transport time… may be beneficial in areas with a high burden of penetrating trauma.”

The study findings are not surprising and are consistent with previously documented evidence that hypotension in patients with major penetrating trauma is a predictor of increased mortality[6] and that early transport to definitive care is recommended.[1-37] The total prehospital time average of 27.09 (SD = 7.79) minutes is also comparable to a previously described US national average of total prehospital time interval of 30.81 minutes for urban ground ambulance transport of trauma victims.[8] This study is however unique in describing a significantly worse outcome (higher mortality rates) with prolonged total prehospital time intervals for a specific subset of trauma patients. The study also identifies indirectly a new performance measure for urban EMS systems to evaluate their trauma triage decision schemes by comparing the total prehospital time intervals of different groups based on ISS and showing that “patients with higher injury severity experienced shorter pre-hospital transport time.”

The study has several limitations. First, the authors under stressed the finding that for the majority (84.2%) of the study population, i.e. normotensive patients with penetrating thoracic injury, prolonged total prehospital time intervals did not adversely affect the outcome but rather a trend towards decreased mortality was observed with increasing total prehospital time intervals. This finding may have exaggerated the relative risk of death described and may be partly explained by the fact that the group of normotensive patients was different from the group of hypotensive patients with regards to the ISS.

Second, the authors chose an emergency department (ED) parameter (first SBP documented in the ED) instead of a prehospital parameter to define hypotensive patients. This has limited applicability to the prehospital setting in terms of identifying patients who may benefit from earlier and faster transport.

A third limitation is related to the retrospective nature of the study and the lack of some prehospital data. The authors did not consider other potential confounders that may affect outcomes in patients with penetrating thoracic trauma such as the advanced life support (ALS) prehospital interventions that were performed on patients including intravenous fluid infusion, endotracheal intubation, and needle decompression.

Finally this study might not change the current processes that US urban EMS systems have in place for prehospital trauma care but it provides evidence for and places further emphasis on the fact that specific subsets of trauma patients may have survival benefit from faster transport and shorter prehospital time intervals. Future prospective studies validating similar findings may help strengthen the link between the existing structural components of trauma systems and specific outcomes in trauma care.