The benefits of HEMS – more evidence!

This post was prompted by two new studies about the benefits of HEMS. For those of you with short attention spans, I’ll give a one-liner on each study then describe them more thoroughly later on.

  1. U.S database study: among severely injured trauma patients (Injury Severity Score >16), HEMS is associated with improved survival rates 
  2. Dutch database study: Reduced mortality among polytrauma patients especially those with abnormal vital signs

The debate surrounding the benefit of patient-oriented outcomes for HEMS is nothing new.  In much of the world, HEMS (helicopter emergency medical services) includes physicians on board the helicopter though in North America often HEMS clinicians are advanced care paramedics. In each country, different models exist and as a result extrapolating findings to our setting is difficult.

One of our BK's that we fly at ARHT

One of our BK’s that we fly at ARHT

It’s easy to imagine that that HEMS (with or without a physician on board) benefits our patients. We bring highly trained clinicians to a scene where we can perform advanced interventions and then rapidly transport the patient to hospital for definitive care. However, studies have demonstrated variable results regarding patient outcomes with HEMS. These differences are undoubtedly affected by the variability amongst HEMS systems around the world. Each HEMS group operates with different thresholds for activation, variable relationships with the local land EMS and then there are a range of geographic and patient characteristics that will affect patient outcomes.

I mentioned above two recent studies that provide additional evidence into the benefits of HEMS. I’ll focus on the Dutch study from the European Journal of Emergency Medicine primarily. They included a consecutive cohort of trauma patients that either HEMS or land EMS responded. It’s not  They used some fancy statistics to calculate lives saved due to HEMS response. It would have been nice to have a more detailed description about their setting as it would allow for more robust comparisons to other centres. It should be noted they had <5% penetrating trauma in their population. It’s unclear how this impacts the statistics but likely critically ill patients who suffered penetrating trauma should be transported to hospital quickly since operative management is likely to be required. They also intubated a large number of their patients when HEMS was on scene (58%). This number was quite surprising. In our setting, we would intubate <10%. Again, whether they have an standard operating procedure or set of criteria for intubation – it would have been good for some discussion about this.

They had fairly reasonable scene times as well. While I don’t think scene times are as important as sometimes they’re made to be especially when necessary interventions are being performed, they at least didn’t spend hours on scene! Interestingly, when we compare the EMS vs. HEMS pre-hospital time there was a 7min difference (42min vs 49min). This is almost entirely accounted for by the extra 7 min that HEMS spends on scene. The authors describe short transport times which suggests that if there truly is a HEMS survival advantage then this isn’t the result of faster transport.

In the U.S study, which has a very different EMS system, they found survival benefit among the most seriously injured trauma patients. I believe there weren’t physicians part of the U.S HEMS model but they probably had advanced care paramedics. Unfortunately the study doesn’t describe the system well. Nonetheless, again using some statistics to account for injury severity, HEMS in the U.S appears to benefit sick patients with altered physiology. It is challenging to interpret U.S data as there’s considerable heterogeneity and financial drivers for HEMS use.

Ultimately we need more prospective data that isn’t fraught with the challenges of using retrospective data – each of these above studies suffer from these limitations. However, there is an emerging trend that HEMS benefits severely injured patients and more importantly, this could be independent of the transport time benefits. This is growing evidence that HEMS is not just an expensive, fast taxi service. Instead, improved patient outcomes may be the result of better clinical expertise brought to the scene.