Welcome to the Polar Vortex 2019 #PoVo19 I hope you are all are staying warm. Since I’ve been seeing more cold, etoh, and confused patients I thought I’d out a quick podcast discussing some hypothermia physiology and prehospital patient care info.
Here are some of the highlights.
Hypothermic Cardiac Arrest:
For every 1°C of hypothermia, metabolic demand will decreased by 6% therefore these patients can tolerate cardiac arrest 10 times longer than at 37°C or 98.6°F (normal body temp). For severe or profoundly hypothermic patients transport to an ECMO Center for rewarming can be life-saving.
For these patients do not apply heat to the head as the decreased metabolic requirements of the cold brain can be neuroprotective.
Because hypothermia protects the brain from hypoxia by reducing brain activity the severely hypothermic patient’s the brain can tolerate circulatory arrest for up to 30 minutes. Full neurologic recovery has been seen from hypothermic patients and reported after 8 hours and 40 minutes of cardiac arrest.
Ideally these patients need continuous CPR, and this is where mechanical CPR (like with a LUCAS device) would be beneficial. If this is not possible, there are conservative recommendations that allowed rescuers time to move the patient to a safer location or allow rest. It severely hypothermic patient’s continue CPR for 5 or more minutes and limiting interruptions to 5 minutes or less is recommended if compressions cannot be administered continuously.
Transport patients to an ECMO Center if they are at higher risk of cardiac arrest, core temperatures less than 28°C or 82.4°F, ventricular arrhythmias, systolic blood pressure less than 90, and if the patient is has already arrested.
There is insufficient data to justify recommendations for cardiovascular drugs and hypothermia below 30°C (you can remember 30 because it looks like someone laying on their back in cardiac arrest) or 86°F.
Rescuers should attempt defibrillation and patient’s with a core temperature 30°C or 86°F or below as there are reports of patient’s with temperatures less than 26°C or 78.8°F who have been successfully defibrillated. We will most likely not be able to get temperatures in the prehospital environment therefore defibrillation should be attempted on hypothermic patients either with an AED or manual defibrillator. This attempt would most likely be the most beneficial with a single shock at maximum power. Reattempts at defibrillation are recommended once the patient has been rewarmed at least 1° - 2°C. Above a core temperature of 30°C or 86°F rescuers can follow standard defibrillation protocols.
There are differing guidelines as to appropriate care for the hypothermic cardiac arrest patient. According to ERC (European Resusc Council) attempt 3 shocks then defer further attempts until pt > 30°C or 86°F and withhold Epi or antiarrythmics until the patient is warmed to 38°C or 86°F.
There is insufficient human data to justify recommendations for cardiovascular drugs in hypothermic patients below 30°C or 86°F. Metabolism of drugs can be decreased and protein binding increase with hypothermia. The worry would be that these drugs given during the hypothermic event may become bioavailable and lead to toxicity once the patient is warmed. It has been recommended that it can be prudent not to give vasoactive drugs to a patient with the core temperature less than 30°C.
Between 30° to 35°C or 86°F to 95°F drugs should be given at normal doses yet consider 2 times the interval in between doses.
In the prehospital setting one cannot be sure which victims of hypothermic cardiac arrest will survive resuscitation attempts therefore it is recommended to we start BLS and consider ALS measures until reaching the hospital with ECMO and rewarming capabilities as long as there are no obvious signs of irreversible death. In hypothermic patient’s one cannot go off of dilated pupils or stiffness as these are unreliable signs of death.
Do not resuscitate if:
There are obvious signs of irreversible death such as truncal transection, decapitation, loss of brain matter, or fully frozen rigid bodies with the inability to compress the chest.
If the patient is in cardiac arrest and their temperatures is greater than 32°C or 89.6°F then hypothermia is less likely to be the cause of their cardiac arrest.
No human with a potassium level > 12 has ever been successfully resuscitated. This can be used as a guideline for in-hospital termination of resuscitation efforts.
There are 4 categories of Hypothermia
Misch, M., Helman, A. CritCases 12 – Accidental Hypothermia and Cardiac Arrest. Emergency Medicine Cases. http://emergencymedicinecases.com/accidental-hypothermia-cardiac-arrest. Published January, 2019. Accessed [date].
Hilmo, J., Naesheim, T., & Gilbert, M. (n.d.). "Nobody is dead until warm and dead": Prolonged resuscitation is warranted in arrested hypothermic victims also in remote areas--a retrospective study from northern Norway. Resuscitation., 85(9), 1204-1211.
Zafren, K. (n.d.). Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia. Emerg Med Clin North Am, 35(2), 261-279.
Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM). (n.d.). Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine., 24(1), Scandinavian journal of trauma, resuscitation and emergency medicine. , 2016, Vol.24(1).
Helicopter picture by Pete Rankin, Flight RN UW-MedFlight