Where does Helicopter Emergency Medical Services (HEMS) make a difference?

Author: Kaleb Lachenicht, Chief Clinical Officer of ROCKET and Director Epic EM

Does Helicopter Emergency Medical Services (HEMS) actually change mortality?

Or do we just feel like it does?

This is a tough question, and especially emotionally loaded when your whole job is HEMS...

We invest heavily in HEMS systems.

We train relentlessly.

We push advanced interventions into the prehospital space.

But when you strip it all back…

Are we actually changing outcomes?

A recent paper finally gives us something more meaningful than opinion.

The Study That Moves the Needle

This large UK-based cohort study looked at over 3,200 trauma patients attended by HEMS over 10 years, and instead of just asking “what was survival?” they asked a better question:

Did patients survive more than they were expected to?

Trauma outcomes are super messy because the patients present with such a host of different injuries and collections of injuries, different physiology and different systems affected.

• Different injuries

• Different physiology

• Different systems

So raw survival means very little.

What They Found (And Why It Matters)

HEMS patients survived more than expected

• Observed survival: 84.7%

• Expected survival: 81.3%

• Excess survivors: +5.23 per 100 patients 

Translated this means: that for every 100 major trauma patients, 5 extra people survived beyond what the model predicted. In a system that flies around 300 trauma patients a year, thats around 15 additional patients surviving when they likely should not have.

That’s not small, especially if you happen to be one of the 15...

The Benefit Is Not Evenly Distributed

This is the part most people miss.

The biggest survival benefit wasn’t in the sickest or the least sick.

It was here:

Moderate-to-severe patients (25–45% predicted survival)

• 35% relative increase in survival 

This has massive implications for:

• Decisions around who should be flown

• Resource allocation

• System design

Not every trauma patient needs HEMS, but some absolutely will benefit.

The Real Clinical Signal

This study isn’t just about helicopters.

It’s about what HEMS brings to the patient.

The key drivers of survival in the patient cohort:

• Younger age

• Higher GCS

• Advanced interventions (completed when needed)

But one stands out:

Pre-hospital Emergency Anaesthesia (PHEA)

• Associated with reduced mortality overall

• Associated with unexpected survival in low-probability patients (OR ~2.0) 

This last one really surprised me, though the system is likely a huge part of this - the resuscitation prior to airway management as well as the focus on bringing the patient closer to the skills required to keep them alive is likely the reason that this intervention seems to have such a big effect on survival in the right patient.

This is the uncomfortable truth:

It’s not the helicopter.

It’s:

• The team

• The decision-making

• The interventions

• The timing

But this is also something we have known anecdotally for the longest time

The Unexpected Survivors

This is my favourite part of the paper, there are patients who should have died… but didn’t.

• 38.7% of low-survival patients (<50%) survived unexpectedly 

These are the patients:

• Who look unsalvageable

• Who challenge your decision-making

• Who test your system

What This Means for Retrieval Teams

This paper reinforces a few things we see every day:

1. Physiology beats anatomy

In low-survival patients

• GCS and age mattered more than injury pattern 

2. Advanced interventions matter... but context matters more

• PHEA was associated with survival

• Blood / thoracostomy was associated with worse outcomes (surprising on the blood part - but it makes sense that without a way to plug the hole - simply increasing the volume is not helpful)

Its important to remember that these interventions don't harm patients, but the findings reflect how sick those patients already are.

3. The “middle group” is where we win

Not:

• The walking wounded

• Not the unsurvivable

But the salvageable critical patient (which is kind of something I think those flying these patients have understood for a long time - without the data to back this up)

That’s where decision-making, skill and timing change outcomes.

4. Traumatic Cardiac Arrest is evolving

• ROSC improving annually

• ~27% achieved ROSC

• ~25% of those survived to 30 days 

We need to move beyond the older teaching of "nothing will save you", to a more nuanced thought process of "What will save this person if I do it early enough?"

TCA is no longer universally futile.

The Leadership Question

This paper is clinical AND it’s operational.

If we accept this data, then we have to ask:

• Are we dispatching HEMS to the right patients?

• Are we investing in the right capabilities?

• Are we measuring performance properly?

Because the reality is: If we measure the wrong thing, we will miss the impact.

The Bigger Lesson About Critical Care Retrieval with HEMS

This study highlights something deeper about critical care retrieval:

• We are not just transporting patients.

• We are changing their physiology before they reach hospital.

This is where we change the outcome.

Bottom Line

• HEMS was associated with 5 extra survivors per 100 trauma patients

• The biggest benefit is in moderate-to-severe injury

• PHEA and advanced care matter in the right patients

• Unexpected survival is real, and significant

• The true value of HEMS is clinical capability, not transport

Final Thought

We often ask:

“Does HEMS make a difference?”

Maybe the better question is:

“Where does HEMS make the difference?”

References

Griggs, J., Harris, J., Barrett, J., et al. (2026). Helicopter Emergency Medical Services attendance is associated with favourable survival outcomes in major trauma: derivation and internal validation of prediction models in a regional trauma system. Emergency Medicine Journal.