Today, I am joined by Ken Zafren to take a deeper dive on accidental hypothermia. I did a podcast on accidental hypothermia way back in episode 66. I also recently did a spot on Crit Care Mailbag on EM:RAP. After that appearance, Ken Zafren reached out to me to discuss some nuanced points on the management of these critically ill patients.
Ken Zafren
Ken Zafren, MD, FAAEM, FACEP, FAWM
Associate Medical Director – Himalayan Rescue Association – Kathmandu, Nepal
International Commission for Mountain Emergency Medicine (ICAR MedCom)
Clinical Professor – Department of Emergency Medicine
Stanford University Medical Center – Stanford, CA USA
Staff Emergency Physician – Alaska Native Medical Center – Anchorage, AK USA
Afterdrop
It is discussed in the attached paper, but succinctly, there was the idea floating around 20 years ago that there could be no active external rewarming in the field due to fear of afterdrop killing the patient and EMS was told to keep the patient cold (in some papers even passive rewarming was to be avoided). This is the myth!
Afterdrop and Active External Warming in the Field
Afterdrop is mostly caused by peripheral vasodilation causing return of cool blood from the extremities to the core.
I have a running disagreement with Doug Brown and his coauthors, all colleagues of mine, because they don't believe that afterdrop is real. They all work in hospital settings, while most of the afterdrop occurs during the prehospital phase. Afterdrop can be important, mostly because it can increase the risk of VF by dropping the core temperature below 28°C.
Afterdrop can be as much as 7.2°C (Meyer et al. 2014).
- Fox et al. A retrospective analysis of air-evacuated hypothermia patients. Aviat Space Environ Med 1988;59(11 Pt 1):1070-1075.
- Baumgartner et al. Cardiopulmonary bypass for resuscitation of patients with accidental hypothermia and cardiac arrest. Can J Surg 1992;35(2):184-187.
- Stoneham et al. Prolonged resuscitation in acute deep hypothermia. Anesthesia 1992;4(79):784-788.
- Meyer M, et al. Sequelae-free long-term survival of a 65-year old woman after 8 hours and 40 minutes of cardiac arrest from deep accidental hypothermia. J Thorac Cardiovasc Surg 2014;147(1):e1-2 (28-20.8C despite insulation and warming in the ambulance – case from Geneva)
You can do whole body forced air rewarming, including the extremities, without increasing the afterdrop. Vasodilation of the extremities is probably minimal unless the patient stands up or the extremities are moved around. That is why we should cut the clothes off rather than pulling them off.
HOPE Score for Prognostication to Decide on ECLS for Accidental Hypothermia
Original HOPE Score Paper
Calculator for HOPE Score
Esophageal Temp Monitoring
must use
Easier Field Classification System
ETCO2
st remembered another critically important recent paper from some of my European colleagues. ETCO2 <10 cannot be used as a criterion for stopping CPR in hypothermic cardiac arrest.
Darocha ETCO2 low PH-stat-PaCO2 hypothermia 2022
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We used to do some “hypothermia labs” for the Diploma in Mtn Medicine course with the “Spot-on” thermometers and in early classes likely pushed people too low. Have some n= 10-15 that after drop is really, occasionally frighteningly, real
Hi Scott, Chris Nickson mentions in L ITFL, that with resuscitation in hypothermia, no drugs should be given until a temp of then 30° is achieved, and a maximum of three shocks. He also says that between 30 and 35° all drugs should be given with double the interval, due to slow metabolism and potential accumulation. This is alluded to by Josh Farkas in the IBCC 2019 where he says to avoid repeated doses during resuscitation of the pulseless hypothermic patient. This makes sense, however I haven’t been able to find a lot else in the literature. is this your… Read more »