The findings in this multisite cohort study of injured patients triaged by EMS suggest that the sensitivity of the Field Triage Decision Scheme is lower than previously described, supporting several studies showing that a substantive percentage of patients with serious injuries are cared for in non-trauma hospitals.23–25
Further, only a minority of major trauma patients were identified by triage steps 1 and 2 (physiologic and anatomic criteria), with steps 3 and 4 (mechanism of injury and special considerations) serving to identify a larger portion of such patients with a modest decrement in specificity. Calculating diagnostic test measures based on triage criteria versus hospital destination also impacted values for triage accuracy at most sites. While trauma systems remain the model for regionalized healthcare, our results suggest that the ability to fully concentrate all major trauma patients in Level I or II trauma centers is not yet optimized. However, these results also raise questions regarding realistic goals for primary (field) trauma triage, the practical ability to fully concentrate seriously injured patients in high-resource hospitals through EMS and the potential role for secondary (hospital-based) triage.
According to ACSCOT, the target for under-triage in a trauma system is less than 5%.19
Under-triage can be defined either based on the ability of field triage criteria to correctly identify seriously injured patients (regardless of transport destination) or based on transport to a major trauma center (regardless of triage criteria). We calculated estimates using both of these perspectives, with generally similar findings. However, changing the definition did impact the apparent accuracy of trauma triage within individual sites. These findings are in contrast to previous trauma triage research suggesting under-triage rates of ≤ 5% for the ACSCOT criteria identifying patients with ISS ≥ 16,21,22
though variability in the triage criteria used, outcome definitions, patient sampling and study designs hamper direct comparisons with many previous studies. Closer examination of under-triaged patients reveal this group to be older, often suffering falls (and to a lesser extent motor vehicle crashes) with little physiologic derangement and relatively high rates of surgical intervention. The regions represented in this study have established trauma systems with demonstrated redistribution of seriously injured patients and improved survival.2,4,10
Therefore, these estimates approximate primary triage accuracy among well-developed trauma systems. It is possible that less established trauma and EMS systems may have different diagnostic accuracy for field triage.
While the accuracy of triage criteria among different age groups continues to be debated, our findings support results from other studies suggesting that under-triage is substantially worse among elders23,25,26
and to a lesser extent among children.24
Whether triage criteria are less sensitive or are applied more selectively to different age groups remains unclear. There are unique issues among older injured patients, including higher risks associated with operative intervention, increased comorbidity burden, greater potential for medical complications, different physiologic responses to injury, unclear benefit of trauma centers,1
and end-of-life considerations, all of which make this population unique. Whether separate elder-specific triage criteria should be used and the benefit of trauma care among seriously injured elders1
remain ongoing questions. As children were also under-triaged at a higher rate than adults in our study, these findings suggest that field trauma triage processes are most effective at identifying adult major trauma patients (18 to 54 years), but lose sensitivity at the ends of the age spectrum.
The rate of over-triage (defined as the proportion of patients with minor injuries meeting triage criteria or those with minor injuries transported to major trauma centers) was lower in this study compared to previous triage research. However, with the large number of injured patients cared for by EMS, even small rates of over-triage can produce large volumes of patients transported to major trauma centers, so consideration of the absolute numbers is also important. Our findings suggest that the field triage criteria are fairly selective in identifying major trauma patients and fall under the < 50% over-triage target set by ACSCOT.19
Comparing over-triage estimates between triage criteria (lower) and transport destination (higher) suggests that while the triage criteria appear to be used selectively, injured patients not meeting triage criteria are still frequently transported to major trauma centers. Notable exceptions are sites B and F, both of which had lower sensitivity and higher specificity for accuracy assessment by transport destination. Such findings suggest that some sites successfully identify most major trauma patients using field triage criteria, but are more selective in transporting these patients to major trauma centers (or integrate lower level trauma centers for the initial evaluation). We recently explored patient transport patterns and found that among patients not meeting field triage criteria, patient/family preference and to a lesser extent hospital proximity have major influence on transport destination, resulting in a substantive number of triage-negative patients being transported to major trauma centers.36
It is also notable that that mechanism of injury and special considerations criteria increased over-triage, but only modestly, while playing an important role in identifying many major trauma patients missed by the physiologic and anatomic criteria.
One likely reason for the differences between our results and those of previous triage research is the sampling frame. We used a comprehensive multi-site sampling strategy to capture all injured patients evaluated by EMS and therefore approximate the true denominator to who field triage guidelines are applied, rather than relying on more restrictive populations. The current sampling design yielded patients with both minor and serious injuries, transported to trauma and non-trauma hospitals and was therefore reflective of the full injured population evaluated and transported by EMS. Our study included both admitted patients and those discharged from the emergency department; the latter group has been excluded from most previous triage studies, but is still subject to field triage processes. We believe these methodological differences provided less biased estimates for triage accuracy and therefore closer approximation of the true performance of field triage, with greater generalizability of the study results. The improvement in specificity may be explained in part by including the broader denominator of patients to whom the triage guidelines are applied (e.g., patients transported to a hospital and subsequently discharged from the emergency department).
Previous triage research has used a multitude of definitions for “serious injury” including ISS ≥ 16,22,37–41
ISS ≥ 20,42
ISS ≥10 plus LOS,43
ISS plus resource use,22,44,45
and strictly resource-based definitions.46–50
This variability in outcomes has reduced comparability between studies. One mechanism to resolve such discrepancies is to link the target group in trauma triage research to the patient population most likely to benefit from trauma center care (i.e., patients with ISS ≥ 16,2,4,7,8,10
AIS ≥ 41
). In concert with this perspective, we used ISS ≥ 16 to evaluate the diagnostic value of field triage in this study. Using an ISS ≥ 16 to define the target population for transport to major trauma centers is also consistent with maximizing the cost-effectiveness of trauma center care.51
Taken together, our findings suggest that there is opportunity for improvement in the field-identification of major trauma patients and matching patient need with hospital capability. However, improving the concentration of seriously injured patients in major trauma centers is likely more complicated than simply revising the triage criteria. There are logistical, financial and philosophical questions built into the optimization of matching need to capacity. A primary logistical question is defining which patients require immediate transport to a major trauma center and the timeliness of trauma center care.52–54
If a window of time exists during which “early” trauma center care still provides an outcome benefit (e.g., < 24 hours), the effective concentration of seriously injured patients in trauma centers may be most efficiently achieved through the combined efforts of primary (field) and secondary (hospital) triage. Our results suggest that the combined primary and secondary triage processes currently fail to fully concentrate major trauma patients in Level I/II trauma centers. These findings point towards a continued opportunity for developing more inclusive trauma systems, improved primary triage processes, formal transfer agreements between hospitals, timely interhospital transport processes, and more objective secondary triage instruments to further optimize the concentration of seriously injured patients in major trauma centers. The cost implications, cost effectiveness and future funding of trauma systems must also be considered. With the cost of care being notably higher in trauma centers51,55
and the cost effectiveness of trauma centers driven by younger patients with more severe injuries (i.e., AIS ≥ 4),51
expanding the field triage criteria to capture ≥ 95% of seriously injured patients runs the risk of substantially increasing the costs of trauma systems (i.e., through over-triage) without improving cost effectiveness. Considering the financial efficiency and costs of a trauma care are necessary aspects of preserving the viability of trauma systems, which continue to face constrained budgets,27
challenges of maintaining on-call panels,56,57
and a declining workforce of trauma surgeons.58
There are limitations in this study that must be considered when interpreting the results. A primary limitation is the retrospective study design. While we applied rigorous strategies for patient sampling, careful attention to identifying patients meeting field triage criteria and matching outcomes to patients regardless of hospital destination, the retrospective nature of the study still limits these findings. In addition, we did not directly measure the frequency of training for EMS personnel on field triage, EMS quality assurance processes and other local EMS factors that likely affect the application and use of field triage criteria. However, the broad inclusion criteria, sampling strategy, and variety of different EMS agencies, hospitals and regions included in this study are a substantial improvement in assessing the diagnostic value of field triage. Prospective efforts to validate the Field Triage Decision Scheme are currently underway.
We attempted to track outcomes for all injured patients transported by EMS, including those subsequently transferred to another hospital, though tracking interhospital transfers was challenging. This process involved delineating which hospital a patient was initially transport to, the location of final hospitalization (if a different hospital) and making certain assumptions about what occurred in between these events (i.e., interhospital transfer). While we were able to provide some assessment of the role of secondary triage in concentrating major trauma patients in Level I and II centers, there may have been additional interhospital transfers that we were unable to identify. Also, the data sources did not allow us to assess the timing of transfer. Furthermore, we did not assess the role of Level III and IV trauma centers and the potential for a tiered or staged process for field triage.
Certain analytic methods (probabilistic linkage and multiple imputation) were central to this study. Both of these methodologies have been well-studied and validated, though there remains the possibility that our findings may be different if outcomes were available for every injured patient evaluated by EMS (i.e., not restricted to patients with a matched hospital record). Because we took a more conservative strategy of restricting the primary analysis to EMS records that matched to a hospital record (including sites that did and did not have ED data available), it is possible that this strategy introduced some selection bias. However, inter-site comparisons did not suggest substantive differences by these factors.