I’m just snuggled up by my fireplace on a cold rainy day which is inspiring me to talk about the cold, specifically hypothermia.
Problems with the cold have been on my mind a lot lately. I did just return from working in Antarctica where it was quite cold. Since being back in California, it has been raining and snowing, a lot. We are being hit by the “atmospheric river,” and while these are relatively warm storms, it is still colder and damper than most people are used to – especially in sunny California. On top of that, I recently attended a lecture by the renowned cold physiology scientist, Dr. Giesbrecht aka Dr. Popsicle, on hypothermia and crevasse rescue[i].
All of this led me to write this article. Let’s talk about what’s going on physiologically when we get cold, discuss the decision process needed to determine when it is causing a problem, and the actions to take to prevent it from becoming something significant (AKA hypothermia).
So, first things first, cold will always be a problem when we are losing heat faster than we can replace it.
Because our bodies love to run at a consistent temperature, we respond to this in two ways- voluntary and involuntary changes.
Voluntary changes are what we consciously do to mitigate becoming cold. They include things like:
- Putting on clothing for protection
- Seeking shelter
- Eating Food
Involuntary responses are things we have no conscious control over. Our body does the work for us once it senses that our core temperature is dropping (losing heat quicker than we can replace it):
- Shell-to-core shunt (prioritizing blood to the core and vital organs)
- Cold diuresis (reduces blood volume by dumping extra fluid)
If all of that sounded confusing, don’t worry, we’re going to break down each of these involuntary responses.
Shivering is an incredibly effective way to generate heat. Shivering can generate 4 to 500 watts of energy (heat). This is probably the most intuitive and obvious way that our body begins to respond when it is getting cold.
Less obvious but equally important, is the shell-to-core shunt. In this process, your body prioritizes sending warm blood to the vital organs – where it is most essential. This will reduce blood flow to the periphery (your extremities), leading to cold hands and cold feet. Your skin may also appear paler or more ashen in color, depending on your skin pigmentation.
The process of sending blood to your core leads to cold diuresis. Cold diuresis acts as a fluid dump. As your body shrinks the size of your vessels in the extremities, there is less space for fluid and some must be released (through urine). You may not have realized this was going on, but you may have noticed needing to pee shortly after going out into the cold. That’s your body’s way of saving warm blood for the vital organs and pushing out extra fluid.
Now let’s talk about Hypothermia
Hypothermia occurs when the core temperature drops to 35°c from 37c°. Some people mistakenly say that you are hypothermic any time your core temperature drops or you start shivering, but that is inaccurate. You must undergo a significant amount of temperature change before you are truly hypothermic.
Here’s a breakdown of hypothermic classification based on core temperature changes:
Cold stress >35° (98.6°f -95°f)
Mild Hypothermia 35°-32° (95°f-89.6°f)
Moderate Hypothermia 32°-29° (89.6°f-82.4°f)
Severe Hypothermia <28°(<82.4°f)
Even after sudden and dramatic cold water immersion (say falling through a lake), it takes a significant amount of time for the core temperature to drop even a degree. Typically it takes more than 20 minutes of immersion.
In less acute exposures, it can take hours or days to begin to see the core temperature start to drop low enough for mild hypothermia.
This is one of the most important ideas I want to get across: Hypothermia takes time.
This means that we can often identify the risk and fix the problem well before it gets to the scary level of hypothermia. All of us have likely experienced cold stress, but very few of us have actually been hypothermic. Thank goodness because as someone who has – it sucks!
Understanding how to identify the difference between Hypothermia and Cold Stress allows us to implement the right treatment.
Anytime we are cold we are likely to experience:
- Shivering – duh!
- Cold hands and feet
- limited dexterity in hands and feet
- Cold faces, affecting mouth movement and speech
All of these symptoms can exist even if core temperatures are relatively stable and normal! I repeat these do NOT indicate hypothermia. They are all normal responses to the body compensating for the cold. Something I am intimately familiar with!
So how then do we tell the difference between a healthy and normal response and a person who is being overwhelmed by the cold and becoming hypothermic? I’ll make it easy….drum roll please…
How alert, oriented, and “with it” are they? If the body’s core temperature dips to the levels of hypothermia, you will begin to see changes in personality and mental status. For example, hypothermic patients will often stop doing anything to self-rescue or care for themselves. They may be quiet, withdrawn, and not self-advocating for help. As they decline, some people may act illogical to their own self-preservation, such as laying down in the cold, removing layers, etc.
These won’t be the only signs. You will see a whole package:
Mild – Moderate Hypothermia:
- Changes in mental status
- Conscious but moving from alert to not alert as they worsen
- Aggressively shivering
- Impaired motor movement (beyond cold hands)
Severe hypothermia is relatively easy. The patient will not be conscious. This patient has exhausted all resources and energy trying to keep warm and they have no more fuel in the tank. Thus, they will also no longer be shivering.
- No longer conscious
- No shivering
- Vital signs may be hard to detect
- Take a pulse for 1min
- Focus on signs of breathing as it may be easier to detect
In all cold patients, you want to eliminate the cold challenge and warm the patient up.
However, once patients are hypothermic there are a few crucial differences[ii]:
Hypothermia presents many challenges for a person’s heart. The muscles of the heart are cold and the blood itself is becoming harder to pump. The longer someone stays cold, the slower blood moves through the extremities. This causes colder blood to pool with more waste products/toxins. If we move these patients roughly or force them to stand or exercise, we may cause cold, toxic blood to rush to the heart. At best, this will just make their hypothermia worst, but at worst it will cause a heart attack![iii] All of this highlights why hypothermic patients need special treatments compared to cold-stressed individuals.
Cold Stress Treatment:
- Add layers to protect better or Remove the patient from the environment
- Give food and water
- Exercise to generate heat
Mild & Moderate Hypothermia Treatment:
- Remove/protect the patient from the environment
- Have the patient stay horizontal and handle them gently
- Add heat to the patient’s layering system
- Only feed the patient if they have the ability to maintain their airway
- Evacuate gently if not improving in 30min-1hr
Severe Hypothermia Treatment:
- Treat as moderate hypothermia
- Evacuate gently and carefully asap
- Evaluate vitals over 60 seconds
- If breathing is detected, move to gentle evacuation
- If no breathing and no pulse are detected, consider CPR if it does not interfere with evacuation
That’s a lot of information, what are the takeaways??
- Pay attention to all the early signs that your body is cold stressed and take ACTION
- My favorite sign is the cold diuresis (needing to pee shortly after going outside). If I notice this, I start thinking about adding layers, eating food, and moving around more.
- Look for mental status changes(#1), ability to move, and length of time exposed to help determine hypothermia in the field.
- Cold stress – make them eat and move their body
- Hypothermia – handle gently
- It’s these two fundamental differences in movement that you really want to consider when helping someone who is obviously cold
- Remove wet clothing if the patient will not be at a hospital or with advanced help in <30 minutes
- Anyone who is unconscious and cold needs to be handled gently and evacuated ASAP!
- Someone who is hypothermic will be at risk for other cold injuries such as frostbite
Please, please, please, take time to plan and prevent this from happening to you. Always look at the weather forecast, bring your first aid kit, pack appropriate layers, and carry extra food and water in case you are out longer than intended. Let people know where you are going and when you plan to be back. I have worked at -76°F and been comfortable with adequate planning, but I have also been out at 40°F and been miserable with poor planning.
For more information on cold stress and hypothermia, check out my video below:
[i] Death After Crevasse Rescue in Antarctica, Gordon G. Giesbrecht, PhD 1 ; Jeffrey R. Brock, MBBS 2
Survival After Being Wedged in a Crevasse for 16 Hours in Alaska, Gordon G. Giesbrecht, PhD ; Ken Zafren, MD; Jaime Anderson ; Chris Erickson
[iii]Witnessed Cardiac Arrest in a Hypothermic avalanche victim