Stages of Hypothermia

There are several different ways of discussing the stages of hypothermia.  In the hospital, stages and severity is mostly defined by core body temperatures.  In the field, core body temperature is difficulty to obtain and exposing a subject to get a rectal temperatures will likely result in a further drop in body temperature.

In the field, we get a good assessment of hypothermia by observing the subject for 5 signs:

• Shivering

• Functioning Normally

• Normal Mental Status

• Conscious

• Signs of Life

From these 5 signs, we can categorize a person into the following stages of hypothermia:

• Functioning Normally (not really a stage)

• Cold Stressed

• Mild Hypothermia

• Moderate Hypothermia

• Severe Hypothermia

• Profound Hypothermia

Functioning Normally

Shivering No

Functioning Normally Yes

Normal Mental Status Yes

Conscious Yes

Signs of Life Yes

This is what  a normally functioning person should look like.  They aren't shivering and seem to be functioning normally. 

They may feel chilly, but they don't have hypothermia. 

Things are good.  Keep them that way. 

Cold Stressed 

Shivering YES

Functioning Normally Yes

Normal Mental Status Yes

Conscious Yes

Signs of Life Yes

The person in question is shivering.  This a natural response to being cold and helps your body create heat.

Shivering alone does doesn't necessarily mean you have hypothermia.  If they are functioning normally, the they are just cold stressed.  They DON'T have hypothermia...at least not yet. 

Take action to get them and others warm.  Have them put on more layers or get moving if you are sedentary.  If they are wet, you should get them dry.  High calorie foods and drinks can be helpful. 

Keep an eye on this person and watch for signs of hypothermia for the rest of your group. 

Mild Hypothermia 

Shivering YES

Functioning Normally NO

Normal Mental Status Yes

Conscious Yes

Signs of Life Yes

Core body temperature has dropped to somewhere around 90-95°F (32-35°C).  Brain functions are now affected by the drop in body temperature.  If you pay attention, you should observe unusual behavior in the subject.  

Look for signs of the '-umbles'

• Fumble

• Grumble

• Mumble

• Stumble

• Tumble

You really don't want to get to this point, but it happened.  If you have access to dry shelter, you should be able to avoid a visit to the hospital.  That said, things can deteriorate and this needs to be taken seriously. 

It is important to note that subjects in hypothermia are extra sensitive to cardiac dysrhythmias.  Handling them roughly can trigger a cardiac rhythm that can result in death. 

Treatment:

• Handle Gently

• Keep Horizontal

• No standing/walking 30 min

• Remove wet clothing if sheltered

• Insulate/vapor barrier as needed

• Heat applied to chest and armpits 

• High-calorie food/drink

• Monitor until better 

• Evac if no improvement

Moderate Hypothermia 

Shivering YES/NO/Maybe?

Functioning Normally NO

Normal Mental Status NO

Conscious Yes

Signs of Life Yes

Core body temperature has dropped to somewhere around 82-90°F (28-32°C).  Brain functions are severely affected by the drop in body temperature.  The now have significant findings of mental dysfunction.

Hard to miss symptoms unless you are also hypothermic:

• Severe '-umbles'

  • Fumble

  • Grumble

  • Mumble

  • Stumble

  • Tumble

• Mild to Severe Confusion

• Movements are slow and labored

• Ataxia (stumbling pace)

You, and more so the subject, have a severe problem now.  The subject can no longer take care of themselves.  Without help, they may very well die.  As body temperature plumets, shivering is affected.  Shivering may be violent or absent.  

Heat generation:

• A resting human body normally produces about 100 watts of heat

• Shivering increases this number by approximately 3-5 times to 300-500W

• A severely hypothermic subject who is not shivering, only generates about 40 watts of heat or less

This subject needs an external heat source and an evac to a hospital. 

Remember that hypothermic subjects are at risk of cardiac dysrhythmias.  Do NOT handle them roughly or try to rub them to get them warm.

Treatment:

• Handle gently

• Keep horizontal

• No standing/walking

• No drink or food

• Remove wet clothing if sheltered

• Insulate/vapor barrier

• Heat applied to chest and armpits

• Evac

IMPORTANT NOTE: DO NOT place subject in a hot bathtub or expose them to a hot shower.  This may seem like a good idea, but can result in circulatory collapse when blood vessels in your arms and legs open up in response to the hot water and blood rushes to fill these blood vessels. 

Severe Hypothermia 

Shivering NO

Functioning Normally NO

Normal Mental Status NO

Conscious NO

Signs of Life Yes

Core body temperature has dropped to somewhere around < 82°F (28°C).  Brain functions are impacted to the point where the subject is no longer conscious. 

This subject is going to die unless you get them to a hospital.

Treatment:

• Handle with Care

• Keep Supine (lying on back)

• If NO breathing/pulse- Start CPR

• Evac to hospital

Profound Hypothermia 

Shivering NO

Functioning Normally NO

Normal Mental Status NO

Conscious NO

Signs of Life NO

Profound Hypothermia is when the subject appears dead.  There are no signs of life.  Core body temperature can drop down to below 75°F (24°C).  It may be possible to rescue this subject and there are many accounts of subjects undergoing hours of resuscitation and surviving despite not having signs of life. 

“a Subject is NOT Dead until Warm and Dead” 

Do what you can to resuscitate your subject and get them to a hospital. 

Treatment:

• Extended CPR required (potentially hours)

• Maintain body temperature if possible during transit

• Rewarm at Hospital

Resources:

• Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update

• Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Frostbite: 2019 Update

• Baby It's Cold Outside - Hypothermia Awareness and Educational Program