Living in Canada a reality we face yearly is that seasonal temperatures drop low enough to cause any number of thermal-related injuries, medical issues, and even death in cases of prolonged exposure. Added to this, in Southwestern Ontario a great number of counties, cities, and towns have large bodies of water that are easily accessible; and even into fall/spring, we can see those waterways with cold enough temperatures to also cause exposure-related issues. 

What is Hypothermia? 

Hypothermia is defined as a core temperature of less than 35°C, but as a person’s temperature drops, changes begin to occur within the body and present with worsening signs and symptoms.  

• Core temperature of 32 – 28°C – Shivering will stop and the patient will display noticeable confusion, drowsiness, and delirium.  
• Core temperature of 28 – 24°C – The patient will lose consciousness, pupils will likely be fixed and dilated (even though a pulse may still be present), and lungs will develop pulmonary edema (tissue fluid leaking into the lungs).  
• Core temperature below 24°C – Profound bradycardia with very weak pulses can occur at this level of hypothermia, however, many may be in cardiac arrest at this point.  If any doubt, treat as a cardiac arrest 

Hypothermic cardiac arrest from cold water exposure/immersion can occur in our region. In these cases, and even in dry hypothermia, hypoxia is often the cause of cardiac arrest rather than the decreased temperature on its own. As with any cardiac arrest, be sure to assess the airway.  Sometimes snow or ice can impede the patient’s airway if they are found buried in snow. 

How do we know when a Hypothermic patient is truly dead? 

In any other cardiac arrest patient, we can look for things like rigor, stiffness in the neck and jaw, unreactive pupils, or even skin colour changes. However, in hypothermia, these signs could lead us to pronounce a patient that could be saved with in-hospital warming, prolonged resuscitation, or even through the use of ECMO (extracorporeal membrane oxygenation). Even having a patient presenting in an asystole rhythm has no significance to the predictability of whether ROSC is possible or not. 

Research tells us that factors to consider for viability of resuscitation in hypothermia can be things like blood potassium over 12, true core temperature below 24°C, and low arterial oxygen levels. However, prehospitally we won’t be able to measure any of these values accurately. So how do we know when not to resuscitate a hypothermic cardiac arrest patient? 

The answer might be surprisingly logical: 

• When the chest wall is frozen to the point CPR is not possible, that patient can be determined not viable and resuscitation efforts withheld (or do not start resuscitation). 
• The scene is unsafe for first responders 
• The patient has other lethal injuries as described in the Obviously Dead Standard 

Final PEARLS for First Responders and Hypothermic Cardiac Arrest 

1. Attempting to vigorously rewarm prehospital will be ineffective. 
2. Do not attempt to forcefully move frozen body parts. 
3. Assess the airway for snow or ice. 
4. Hypoxia is typically linked to hypothermic cardiac arrest, supplemental O₂ will be a favorable intervention. 
5. Do not rely on the typical signs of death: asystole, fixed and dilated pupils, stiff appendages, rigor-like neck and jaw, or even skin discoloration. 
6. The leading sign indicating when to withhold resuscitation efforts: Frozen chest wall and inability to perform CPR due to rigidity of the chest wall.