This post wasn’t an expected one for me. However, there have been a few hypothermia cases recently that motivated me to dig into this topic. This post will be a little more wordy, unfortunately. I admit that I completely nerded out on the reading and podcasts. But, I needed to find the most up-to-date info and answers. And I’ve posted it here for others to benefit as well
DEFINITIONS OF HYPOTHERMIA
- Cold Stressed: 95-98.6 degrees (35-37 Celsius)
- Mild hypothermia: 90-95 degrees F (32-35 Celsius)
- Moderate hypothermia: 82-90 degrees F (28-32 Celsius)
- Severe hypothermia: below 82 degrees F (28 Celsius)
- (Some Sources) Profound Hypothermia: below 75 degrees F (24 Celsius)
Other sources will classify hypothermia in the Swiss system as Hypothermia (HT) 1, HT2, HT3, HT4, and HT5. Either way, hypothermia is usually described based on core temperature. However, this method may not be relevant or practical in assessment.
The American Heart Association defines hypothermia differently with different temperatures. However, the takeaway is that the AHA does not believe that defibrillation is likely to succeed until the patient is warmed above 30 degrees Celsius.
This podcast (A podcast taught by Emergency Department Physicians) suggests describing the diagnosis in more of a symptoms-based approach instead. This is in agreement with the overall direction and attitude of most of the recent articles that I reviewed. This podcast is great because they break everything down in 20 minutes, and they describe a lot of the symptoms. This is a MUST LISTEN TO podcast, in my opinion. You can read the show notes of the podcast also which are very helpful.
The degree of sluggishness and impairment is likely varied amongst individuals, so it is very difficult to diagnose. However, a proper diagnosis does have practical implications because there are different recommendations based on severity of hypothermia.
Rectal temperatures are unreliable for the core temperature in hypothermia patients, and exposing the patient to the cold may worsen the problem. Instead, we should probably focus more on symptoms and clinical picture more than the absolute measured temperature.
Current Recommendations and Protocols
The US Army has a Standard Medical Operating Guideline on Hypothermia for Flight paramedics. Mostly helpful. A good starting point. Posted below:
The SMOG is pretty good, except that medics on the ground don’t usually have the ability to perform an EKG. And being an algorithm, it is not full of details. Still, it’s a good starting point.
I also recommend this “COLD CARD” from the Wilderness Medicine Society. It is excellent and practical. Useful for assessment and treatment. THIS IS A MUST HAVE. Download it for free here.
CONTROVERSIES REGARDING HYPOTHERMIA
There is some disagreement regarding the diagnosis of mild vs. moderate hypothermia, and how to approach this patient. The controversy surrounds the idea of “Afterdrop.”
Afterdrop, the continued fall of deep body temperatures during rewarming after hypothermia, is thought to endanger the heart by further cooling from cold blood presumed to be returning from the periphery.Webb, P. (1986). Afterdrop of body temperature during rewarming: an alternative explanation. Journal of Applied Physiology, 60(2), 385–390. doi: 10.1152/jappl.19220.127.116.115
The controversy is centered around the question: Is it safe to walk a mildly hypothermic patient? The Clinical Practice Guidelines by the Wilderness Medicine Society suggest that a patient should rest in a sitting or prone position for 30 minutes while warming in order to minimize afterdrop. However, some dispute this idea because it may be more important to move out of a dangerous situation and out of the elements. Also, the effects of “Afterdrop” may be overstated. Still, the 2019 update to the Clinical Practice Guidelines by the Wilderness Medicine Society left this recommendation in place.
After reading, it appears that it may be wise to not move the extremities or walk the patient in mild hypothermia, if possible. If necessary to move due to danger to the patient, or further harm to the rescuers remaining in the elements, then the risk should be assumed. Unfortunately, the studies are very limited and the data is lacking support. It is obviously unethical to perform studies by inducing hypothermia (harm) in controlled studies.
MANAGEMENT OF HYPOTHERMIA
THEY’RE NOT DEAD UNTIL THEY’RE WARM AND DEAD”
- COLD STRESSED
- Passive or active warming. Remove wet clothing. Provide a high-calorie food or drink. Move around and exercise to warm up.
- MILD HYPOTHERMIA
- Have patient lie down or sit for 30 minutes. Actively warm to head and trunk/chest. Use a vapor barrier, if possible. Can give warm PO high calorie fluids or food due to possible hypoglycemia. Evacuate if no improvement.
- If the patient is already walking, or if the scene is unsafe, proceed with movement out of the harsh elements to safety.
- MODERATE HYPOTHERMIA
- Be careful with movements of the patient. Keep the patient horizontal. No drink or food. Parenteral glucose in I/O or IV. Heat the trunk/head/chest. Use the vapor barrier. Give warmed IV fluids at 40-42 degrees Celsius (around 104 F). Must be evacuated.
- SEVERE HYPOTHERMIA
- Treat the same as moderate hypothermia, except that CPR may be needed. If there are no obvious signs of breathing or pulse, then begin CPR. An AED may be used to assist. The rhythm may not convert in less than 30 degrees Celsius (86 F), until warmed. Evacuate immediately. Be wary of complications and arrhythmias, most common is V-Fib.
- Maintain compressions for 5 minutes before moving, and then ensuring that the compressions resume within 5 minutes. Severe hypothermic may be able to tolerate interruptions due to lower metabolic requirements. However, this buffer will fade as the patient warms.
The above guidelines are a collaboration of the sources previously described or are cited below. My main source, and the one article that everyone should read, is the Clinical Practice Guidelines from the Wilderness Medical Society. As always, I would recommend reading through all of the sources in entirety. And keep in mind that the patient could have other reasons for collapse, V-Fib, or asystole besides hypothermia.
Who Needs to Be Evacuated?
Well, this is the big question. And it depends on who you ask/read. According to Dow et al:
” A shivering patient with impaired consciousness should be treated for moderate, not mild, hypothermia.”Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update
Dow, Jennifer et al.
Wilderness & Environmental Medicine, Volume 30, Issue 4, S47 – S69
This is a bit murky because we already established that there are different levels of impaired consciousness, and that individuals respond differently. Additionally, the same article describes mild hypothermia as “still shivering” in most cases. Therefore, I believe that it is prudent to err on the side of caution and refer a patient who has become sluggish and impaired/slowed to the Emergency Room for further evaluation and workup.
What Actions Should Be Taken Now?
I am definitely going to conduct some more training with my medics by asking them to read this information, the articles, and to listen to the podcast. We will also try to develop some hands-on training scenarios with a mannequin in a severe hypothermia situation.
I may also redesign some cold weather training for the non medical guys/cadre. I would recommend others do the same since the scenario, if encountered, may be complex.
We will ensure that we stock all of our vehicles with active external warming equipment. I’ll be looking to purchase more HYPOTHERMIA PREVENTION AND MANAGEMENT KITS (HPMK) from North American Rescue since it is most easily transportable. It provides 10 hours of active warming once activated by oxygen (Anyone can buy from the NAR website or from Amazon.com). And, I’m going to look at this low profile alternative to the thermal angels. It’s basically IV tubing warmed with coils from what appears to be a slimmer-profile battery (sold by North American Rescue).
- Durrer, B., Brugger, H., Syme, D., and International Commission for Mountain Emergency Medicine. The medical on-site treatment of hypothermia: ICAR-MEDCOM recommendation. High Alt Med Biol. 2003;4: 99–103
- Soar, J., Perkins, G.D., Abbas, G., Alfonzo, A., Barelli, A., Bierens, J.J. et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation. 2010; 81: 1400–1433
- Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. Dow, Jennifer et al.Wilderness & Environmental Medicine, Volume 30, Issue 4, S47 – S69
- Hypothermia Evidence, Afterdrop, and Practical Experience. Brown, Douglas et al. Wilderness & Environmental Medicine, Volume 26, Issue 3, 437 – 439
- Hypothermia Evidence, Afterdrop, and Guidelines. Zafren, Ken et al. Wilderness & Environmental Medicine, Volume 26, Issue 3, 439 – 441
All content is intended to be educational only. Medics should operate under the supervision of a medical provider and abide by all local laws while stateside. Medics should only practice at the level credentialed, and only at the level allowed. This content is not intended to treat or give a substitution for any credentialed provider. Content is intended to aid in a deployed prolonged care setting. Take guidance from your leaders. Utilize these posts as preparation and as a supplement to your provider’s direction and teaching.