This study represents the first population-based EMS study to evaluate the natural history of trauma patients accessing the emergency 9-1-1 system who are not transported the hospital. These patients are important to study as they represent a population that is invisible to trauma registries and databases currently used to evaluate trauma systems. We found the rate of non-transport to be approximately 9% of all ambulance dispatches for trauma. Thirty percent of these patients later presented to the hospital and/or died. Based on our estimates for linkage match rate, our values are conservative and the true rates of emergency room visits, admissions and mortality may be higher.
The findings in the current study are consistent with other studies that have looked at non-transports in other populations. The rate of non-transports in mixed medical/surgical patients ranges from 5%-48%.2,3,10-12
For patients not transported after an EMS dispatch, 20-59% were seen by a medical professional within seven days.1-3
Knight et al. performed a population-based study of all EMS dispatches (medical and surgical) where patients refused transport in the state of Utah from 1996-1998.3
They found that 5% of patients refused transport. Of these patients, 20% were seen in an ED within 1 week, 1.2% were admitted, and 0.2% died. Trauma calls comprised 20% of their population, but almost 50% of the transport refusals involved a motor vehicle collision (MVC).
Similar to the study discussed above, the mortality rate for non-transported patients in the current study was 0.2%. This translates into a mortality rate of 0.02% for the entire injured population. Information about the death was available for only four of these patients. The time to death in these patients averaged 8 months, which suggests that trauma was not the proximate cause of death. Furthermore, two patients had a do-not-resuscitate status which suggests death was due to a pre-existing condition. However, it cannot be determined if trauma was the cause of death for the three patients for whom data was not available.
There appeared to be certain characteristics associated with emergency room visits and admission to the hospital after non-transport. Victims of violent crimes and pedestrian accidents were more often seen in an emergency room and discharged after non-transports (versus MVCs and falls). It is possible that these mechanisms of injury induce a psychological need to be seen that becomes apparent after the ambulance has left the scene.
Also, increasing age is more likely to be associated with an increasing likelihood of admission and a decreasing likelihood of being seen and discharged from an emergency department after non-transport. All patients under one year of age that were not initially transported were later evaluated at an acute care hospital, compared to 15% of patients older than 65. These data suggest that EMS providers be more aggressive in cases with a higher likelihood of delayed presentation to the hospital.
We do not know whether non-transport is initiated by the patient or the EMS provider because the reason for non-transport was not recorded by the EMS providers. It is possible that the majority of non-transports in our study were initiated by the patient because barriers do exist for EMS providers in our region to not transport. For example, EMS providers are encouraged to contact a physician prior to deciding not to transport. Furthermore, the majority of EMS dispatches were conducted by a single private ambulance company with a financial incentive to transport. It is also possible that alcohol and social circumstances may have played a role in patients refusing transport. However, there are protocols in place within our system to determine if a patient has decisional capacity to refuse treatment.
Other studies have evaluated the reasons for non-transport. Pringle et al. conducted a prospective observational study of all EMS calls to determine whether non-transports were patient or medic-initiated. They found 66% of non-transports were patient-initiated. Schmidt et al. evaluated patients who were not transported after an EMS dispatch and followed patients up by a telephone survey to determine the reasons for non-transport.2
They found that 53% of the non-transport patients refused transport because they felt it was not necessary. An additional 6% cited the cost of the ambulance as the reason for refusal. The remainder was divided between EMS provider judgment (14%) and other reasons. It is possible that the majority of refusals are in our population are initiated by the patient for reasons similar to previous studies.
Also, it appears that when a patient is not transported but eventually seek care, they do not present to trauma hospitals. This may be due to many factors including the fact that many trauma centers are county hospitals, the presence of closer non-trauma hospitals, and lack of knowledge by patients about trauma regionalization. It is interesting that once non-transports present to non-trauma hospitals, they often remain there as fewer than 1% were transferred.
There are many limitations to this study. One of the most important limitations is that we do not know the reason for non-transport. Without this information, it is difficult to provide feedback and improve trauma systems. One process that is changing in our system is that the electronic records are going to force ambulance personnel to fill in all important fields. We are hoping that with this change, full information capture will allow us to better understand reasons for non-transport and will inform future protocol changes.
Trauma registry data can have inconsistent records on complications and diagnoses. Data from OSHPD contains administrative data but lacks hospital-based data such as patient physiology and is limited in the number of diagnoses it contains. Another limitation is the process of probabilistic linkage is the disparate data sources. We are not able to determine the “true” matches and non-matches for any site as such information would have required access to the original medical records. However, the validity of probabilistic linkage using identical software and approach to linkage analysis has a low mis-match rate (high specificity) across a variety of linkage scenarios.8
Our estimated match rates (sensitivity) for this region are high. 9
Though we were unable to directly estimate specificity of the matches; we believe specificity remained high based on the previous linkage assessment at one study site.8
In conclusion, patients who are not initially transported to the hospital after an ambulance is dispatched for trauma often present to a non-trauma hospital later for evaluation and admission. These patients represent an invisible population of patients that previously have not been studied and should be considered when evaluating the performance of trauma systems.