Helicopter Transport Increases Survival for Specific High-Risk Trauma Phenotypes

Refining Prehospital Triage for Aeromedical Evacuation

The decision to utilize air medical transport involves a complex calculation of clinical benefit against resource intensity and cost. While helicopter emergency medical services are associated with improved survival in specific populations, such as those with severe traumatic brain injury [1], the overall accuracy of medical dispatch systems remains variable across different trauma systems [2]. Identifying which patients will become unexpected survivors requires a nuanced understanding of early injury characteristics and the impact of prehospital interventions [3]. Furthermore, the utility of standard tools like the Glasgow Coma Scale (a clinical scale used to measure a patient's level of consciousness) in the early prehospital phase can be limited when predicting specific radiographic injuries in the setting of concomitant shock [4]. To optimize resource allocation, researchers have now identified specific clinical phenotypes within standard triage criteria that derive the most significant survival advantage from air transport.

Identifying Heterogeneity in Triage Criteria

While air medical transport has demonstrated a survival benefit for select patients, clinicians often face challenges in determining which individuals within a broad triage category require this resource-intensive intervention. The Air Medical Prehospital Triage score currently serves as a validated tool to identify patients likely to benefit from air transport, yet the population meeting these criteria remains heterogeneous. Because patients with a positive triage score may experience different levels of benefit, researchers sought to identify specific phenotypes of injured patients who demonstrate differential survival advantages when transported by air compared with ground emergency medical services. The study utilized data from the Pennsylvania Trauma Outcomes Study spanning 2000 to 2017, encompassing a total of 22,569 patients. To ensure a relevant comparison between transport modes, the researchers included patients aged 16 years or older who were transported from the scene over distances greater than 3 miles but less than 40 miles and who met the established triage score criteria. Within this large cohort, 7,607 patients (35%) actually underwent air medical transport, while the remainder were transported via ground emergency medical services. To delineate distinct clinical profiles within this population, the authors employed two advanced statistical techniques: latent class analysis (a method used to identify unobserved subgroups or hidden phenotypes within a population) and k-modes clustering (a technique for grouping data based on categorical variables rather than continuous numerical values). By applying these methods, the researchers aimed to move beyond broad triage categories and pinpoint the specific physiological and anatomic characteristics that correlate with the highest survival benefit from air medical evacuation.

Survival Benefits Across Clinical Phenotypes

The researchers assessed the association between in-hospital survival and actual transport mode using multilevel generalized linear models, which are statistical frameworks that account for data clustered at different levels, such as patients treated within various trauma centers. To ensure the findings specifically reflected the impact of the transport modality, these models were adjusted for demographics, injury characteristics, vital signs, and in-hospital variables. Through the application of latent class analysis, the study identified five distinct phenotype classes among the 22,569 patients who met the initial triage criteria. Two of these subgroups demonstrated a particularly high survival advantage when transported by air rather than ground. Class 2, which was composed of patients presenting with both physiological and anatomic triage criteria and a Glasgow Coma Scale score of 13 or less, showed a significant survival benefit with an adjusted odds ratio of 1.83 (95% CI, 1.41 to 2.36). An even greater benefit was observed in Class 5, a phenotype defined by a Glasgow Coma Scale score of 13 or less plus an abnormal respiratory rate. For these patients, air medical transport was associated with an adjusted odds ratio for survival of 2.23 (95% CI, 1.76 to 2.81). For the practicing physician, these data suggest that the presence of neurological impairment combined with either respiratory distress or multisystem anatomic injuries serves as a critical indicator for prioritizing air medical resources to maximize patient survival.

Validation and Consistency of High-Benefit Groups

To ensure the robustness of the phenotype identification, the researchers employed k-modes clustering as a secondary analysis. This approach also resulted in five distinct classes, mirroring the structure of the latent class analysis. Within this framework, Classes 2, 4, and 5 were identified as the high-benefit groups. These clusters were composed of patients presenting with physiological plus anatomic criteria, a Glasgow Coma Scale score of 13 or less, and/or an abnormal respiratory rate. The survival benefits observed in these clusters were substantial and statistically significant. Class 2 demonstrated a survival benefit with an adjusted odds ratio of 1.85 (95% CI, 1.33 to 2.59), while Class 4 showed an adjusted odds ratio of 2.02 (95% CI, 1.49 to 2.73). The most pronounced effect was seen in Class 5, which reached an adjusted odds ratio of 2.5 (95% CI, 1.97 to 3.17). To further validate these membership assignments and ensure the findings were not limited to the Pennsylvania cohort, the researchers performed the same analysis separately on data from the National Trauma Data Bank. This external validation illustrated similar results, confirming that these specific clinical phenotypes consistently experience improved outcomes when prioritized for air medical evacuation across a broader national population.

Prioritizing Resources for Maximum Clinical Impact

The identification of these specific phenotypes provides a data-driven framework for triage officers and emergency physicians tasked with the high-stakes allocation of limited aeromedical resources. The researchers conclude that patients presenting with a Glasgow Coma Scale score of 13 or less in combination with an abnormal respiratory rate, or those meeting both physiological and anatomic triage criteria, should be prioritized for air medical transport. This recommendation is rooted in the substantial survival advantages observed in these specific cohorts, such as the adjusted odds ratio of 2.23 (95% CI, 1.76 to 2.81) for patients with neurological impairment and respiratory distress, and the adjusted odds ratio of 1.83 (95% CI, 1.41 to 2.36) for those with combined physiological and anatomic injuries. By focusing on these high-risk clusters, clinicians can ensure that helicopter transport is reserved for those who derive the most significant clinical benefit, moving beyond broad triage protocols that may inadvertently prioritize lower-risk patients. The consistency of these findings across both the Pennsylvania Trauma Outcomes Study and the National Trauma Data Bank suggests that these criteria are robust indicators of survival benefit across diverse trauma systems. For the practicing clinician, these data emphasize that the presence of a Glasgow Coma Scale score of 13 or less alongside respiratory or structural distress represents a critical threshold where the speed and specialized care of air medical transport most effectively mitigate the risk of in-hospital mortality.

References

1. Fritz CL, Rosen CL, Thomas CE, et al. Helicopter EMS for scene response to head-injured patients: systematic review & meta-analysis. BMC Emergency Medicine. 2025. doi:10.1186/s12873-025-01392-9

2. Bohm K, Kurland L. The accuracy of medical dispatch - a systematic review. Scandinavian Journal of Trauma Resuscitation and Emergency Medicine. 2018. doi:10.1186/s13049-018-0528-8

3. Gruen D, Guyette F, Brown JB, et al. Characterization of unexpected survivors following a prehospital plasma randomized trial. Journal of Trauma and Acute Care Surgery. 2020. doi:10.1097/TA.0000000000002816

4. Iyanna N, Donohue JK, Lorence JM, et al. Early Glasgow Coma Scale Score and Prediction of Traumatic Brain Injury: A Secondary Analysis of Three Harmonized Prehospital Randomized Clinical Trials. Prehospital Emergency Care. 2024. doi:10.1080/10903127.2024.2381048