Cardiac emergencies, CPR, AEDs & cold stress
Valentine’s Day is about hearts, as well as chocolate and flowers.
So let’s talk about the one heart that actually matters when things go wrong outdoors.
Cardiac emergencies don’t just happen in hospitals or gyms. They happen on hill days, during DofE expeditions, on Scout camps, at outdoor centres, and on winter walks close to home.
And when they do, it's all on you — at least initially.
This post looks at:
Sudden cardiac arrest in outdoor settings
Why early CPR and AED use saves lives
How cold stress and hypothermia complicate cardiac emergencies
What outdoor professionals and adventurers should realistically focus on
Sudden cardiac arrest outdoors – the reality
Sudden cardiac arrest (SCA) is an electrical failure of the heart, not a heart attack (a myocardial infarction). The casualty becomes unresponsive and stops breathing normally. Without immediate intervention, death follows rapidly¹.
In the UK:
Out-of-hospital cardiac arrest survival remains below 10%²
Survival doubles or triples with early bystander CPR³
Each minute without CPR reduces survival by 7–10%⁴
In remote or cold environments, delays in advanced care mean early bystander intervention is even more critical.
However, the context of cardiac arrest outdoors matters.
In outdoor and adventure settings, cardiac arrest is often the end point of another problem, rather than a primary cardiac event. Trauma, cold stress, prolonged exertion, dehydration, hypoxia, and environmental exposure are common precipitants — even in people who appear fit and healthy.
This doesn’t mean chronic cardiac disease is irrelevant. Undiagnosed coronary disease is common, even in active populations (think professional football players), and may act as an underlying vulnerability. What differs outdoors is that acute stressors — cold, injury, altitude, immersion, or fatigue — often trigger the electrical collapse, rather than chronic illness acting alone.
For outdoor professionals and adventurers, this reinforces a key principle:
Cardiac arrest outdoors is frequently secondary to environmental or traumatic issues— but the response remains the same: early CPR and early defibrillation save lives.
Understanding this helps prioritise:
Rapid recognition of collapse
Immediate CPR
Early AED use
Simultaneous management of exposure, trauma, and reversible causes
Because when help is delayed, what you do in the first minutes matters more than why the heart stopped.
(This will be covered in more detail in future blog...)
CPR – simple, brutal, lifesaving
High-quality CPR:
Maintains minimal cerebral and coronary perfusion (oxygen to the brain and heart)
Improves the likelihood that defibrillation will be successful
Current UK guidance emphasises⁵:
Early recognition and call for help
Chest compressions at 100–120 per minute, 5–6 cm depth
Minimal interruptions
In outdoor environments, CPR is often:
Physically demanding
Conducted on uneven or cold ground
Delivered by teams rather than individuals
Training in realistic outdoor scenarios improves performance under stress and reduces hesitation⁶.
AEDs – the biggest survival upgrade
Defibrillation is the only effective treatment for shockable rhythms such as ventricular fibrillation⁵.
Key points supported by evidence:
AEDs are safe and highly reliable
They will not deliver a shock unless indicated
Earlier defibrillation is the strongest predictor of survival⁷
Cold, wet, or muddy environments are not contraindications to AED use. Adaptation is required, not delay:
Expose and dry the chest quickly
Remove excessive hair only if pads will not adhere
Manage insulation and exposure without interrupting CPR
Cold stress – the hidden cardiac risk
Cold exposure causes predictable physiological responses⁸:
Peripheral vasoconstriction
Increased cardiac workload
Higher risk of arrhythmias in susceptible people
Hypothermia also complicates assessment and resuscitation:
Slow heart rate and reduced respiratory rate can mimic death
Defibrillation may be less effective below 30°C
Prolonged resuscitation may be appropriate in cold casualties⁹
The long-standing principle remains valid:
“They are not dead until they are warm and dead.”⁹
For outdoor first aiders, this reinforces the importance of:
Early insulation and shelter
Simultaneous life-saving interventions
Avoiding premature termination of care — especially following prolonged burial or immersion, where a clear airway or an air pocket may indicate hypothermic rather than hypoxic cardiac arrest.
What should outdoor professionals focus on?
You don’t need advanced cardiology knowledge.
You need competence under pressure.
Evidence-based priorities:
Early recognition of cardiac arrest
Immediate CPR
Confident AED deployment
Effective team leadership
Exposure and cold management
Skill fade is well documented, particularly for low-frequency, high-impact events like cardiac arrest¹⁰. Regular refreshers and scenario-based practice are essential.
A Valentine’s reminder that matters
Hearts fail.
People panic.
Training shows.
If you work or spend time outdoors, staying current with CPR, AED use, and cold casualty care is one of the most meaningful things you can do.
Because when it happens — it's all on you, and all you can do is your best.
“We do not rise to the level of our expectations. We fall to the level of our training.”
Be Adventure Ready.
References
Resuscitation Council UK. Adult Basic Life Support Guidelines (2021, updated 2023).
NHS England. Out-of-Hospital Cardiac Arrest Outcomes in England.
Hasselqvist-Ax I et al. Early CPR and survival after OHCA. N Engl J Med, 2015.
Larsen MP et al. Predicting survival from cardiac arrest. Ann Emerg Med, 1993.
European Resuscitation Council. ERC Guidelines for Resuscitation (2021).
Perkins GD et al. CPR quality and performance under stress. Resuscitation, 2012.
Weisfeldt ML et al. Public access defibrillation and survival. Circulation, 2010.
Castellani JW, Young AJ. Human physiological responses to cold exposure. Compr Physiol, 2016.
Wilderness Medical Society. Practice Guidelines for the Prevention and Treatment of Accidental Hypothermia (2019).
Arthur W et al. Decay of CPR skills over time. Hum Factors, 1998.
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