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11 Steps To Do A Hypothermia Wrap (Hypo Wrap)

By Alex Traynor, Boreal River Rescue

Hypothermia wraps, also known as hypo wraps, are a great way to keep someone warm in the backcountry. Whether you are dealing with mild hypothermia, severe hypothermia, or someone with an immobilizing injury at risk of getting cold, the hypo wrap can be an effective way to keep someone warm.

In the following video, we take you through a demonstration of how to do a hypo wrap. It is important to know that there are many different variations of the hypo wrap and this is just one example.

4 Mechanisms For Heat Transfer

Hypo wraps keep subjects warm against the four ways our bodies loose heat. Understanding each of these four areas helps us get a better understanding of the components that make up a hypo wrap. Let’s dive in to take a closer look at these mechanisms for heat transfer and how the hypo wrap addresses them.

1. Conduction

Conduction occurs as a heat transfer between objects that are in contact. The denser the object the faster the heat energy will be transferred. A great example would be individuals who are lying on the ground injured. While it could be a warm summer day, having someone lying straight on the ground can actually cool them off very quickly.  Getting subjects off of the ground by using a foam pad or camping air mattress, will help keep them warm as the pads are less dense than the ground.

In circumstances where somebody is in water, they will loose heat at an exponential rate in comparison to the air, which is why it is so important to remove them from the water as soon as possible.

2. Convection

Convection is the transfer of heat from moving fluids such as air and water. A great way to understand convection would be the wind chill factor. You might take a layer off because the sun is out, but once a gust of wind comes by you start to feel cold and want to put a layer back on. This is your body losing heat to the air moving past you. The outer tarp layer of the hypo wrap works with the inner layers to reduce heat transfer from the elements like wind and rain.

3. Evaporation

Water evaporating from your skin (in the form of sweat) is a very effective mechanism for cooling your body. When we are hot, we want our bodies to do this, but when we are cold we don’t want this. In order to reduce evaporation, we add a vapour barrier around the subject before putting them inside a sleeping bag. This will stop the water from evaporating and keep the hypo-wrapped subject warmer.

4. Radiation

Radiation is the heat energy that is emitted (in the form of waves) and absorbed by all objects. Having thick dense layers of clothing along with sleeping bags can help to absorb and reflect heat energy back to the individual helping to keep them warm. Certain materials do this better than others. Wool, polyester, and down (when dry) are materials that insulate well.

Maintaining vs. Generating Heat

In order to protect someone in a cold environment it is important to consider all of the different mechanisms for heat transfer. The hypo wrap has been made to address each of these four areas to help keep injured or hypothermic people from losing heat, but you also need to consider how the person will generate heat.

When you’re cold, the body’s natural reaction is to shiver to help you warm up. The body needs ‘fuel’ in order to shiver, which stresses the importance of eating calories and drinking fluids.

In severe hypothermia, a person will eventually stop shivering. The person at this point will no longer be awake. This is an emergency that requires immediate evacuation to advanced medical care. The treatment includes:

  • Emergency evacuation to hospital rewarming
  • Hypo wrap
  • Treat the patient gently (the cold heart can be thrown into an abnormal rhythm if jostled)
  • Don’t do anything that will delay evacuation

Any heat that you can add to the packaging is considered good, as long as it doesn’t delay evacuation. Research has shown that it is best to place the heat source directly on the centre of the person’s chest.

11 Steps For A Hypothermia Wrap

  1. Tie a knot in the end of a long rope and weave it back and forth spanning the length of the subject or foam/pad they will be lying on.
  2. Lay down a large tarp completely covering the rope that had been lying down. In many cases the larger the tarp the better as you would rather have more to work with than less.
  3. Put down a foam pad or sleeping pad to elevate the subject from the ground.
  4. Add a sleeping bag on top of the foam pad. If you have multiple sleeping bags, put one down for the subject to lie on top of, and a second for the subject to go inside of.
  5. In some circumstances you may want to add a diaper to the subject before putting them inside the hypothermia wrap. A garbage bag can come in handy, ripping holes in the bottom corners for their feet to go through.
  6. Before putting the subject inside the sleeping bag, you will want to use another tarp to create a vapour barrier, helping to reduce heat transfer from evaporation.
  7. Once inside the vapour barrier you can put them in the sleeping bag and zip it up.
  8. Adding a heat source inside the packaging can be a good idea (as long as it doesn’t delay evacuation or burn the person). The best placement is right on the centre of the chest.
  9. Start wrapping the subject using the tarp on the outside. You will want to take your time and do this well, ensuring the individual is completely protected from the elements like wind and rain.
  10. Once inside the tarp, use the rope to create a daisy chain, working your way up until the tarp is completely secured from the subject’s feet, up to their neck. You want to leave the top open to create a hood.
  11. The final step is to create a hood for the subject. This can be done by placing a SAM splint or stick in the top of the tarp and rolling it up towards their head until all the slack tarp is gone. Tuck each of the rolled ends into the rope of the daisy chain to secure them in place. You can leave the hood like this or, if there is rain or wind, you may wish to unroll the hood to create a cover over their head.