Written by: Luke Neil, MD (NUEM PGY-2) Edited by: Quentin Rueter, MD, (NUEM PGY-4) Expert commentary by: Kory Gebhardt, MD
This is a good overview of the algorithmic approach to the hypothermic patient. Generally speaking, hypothermia can be divided into various categories of severity, but as you mention, it is really those patients with a core temperature of <32°C (90°F) with cardiac instability or cardiac arrest that will require especially aggressive care.
For any hypothermic patient, the most important initial intervention is to stop any further heat loss. This is especially important for those with damp or wet clothing. Any wet garments should be completely removed, the patient should be dried, and then covered with warm, dry blankets and possibly a forced air rewarming device (i.e. Bair Hugger). Recall that one of the most efficient ways to cool a HYPERthermic patient is with evaporative cooling (spraying with or submerging them in water and then using fans to circulate air over the wet surfaces). Similarly, this heat loss will strongly work against you in rewarming a hypothermic patient if they are not fully dry. After this simple intervention, the majority of mildly hypothermic and stable patients just need time to bring their core temperature back to normal and often can be discharged once this has occurred.
For those patients with a core temp >32°C with severe cardiac instability or in cardiac arrest, you should also consider alternative etiologies for their presentation rather than expect it solely caused by the hypothermia alone. Like you mention, if you are able to rewarm a cardiac arrest patient above this temperature and they remain in asystole, it is likely that irreversible damage has occurred and they are less likely to be able to be successfully resuscitated.
As you detail in the algorithm, those with a temperature less than 32°C (90°F) AND instability or arrest need aggressive and invasive rewarming. The best available means of doing this is ECMO. Much of the research surrounding accidental hypothermia and resuscitation comes from the Nordic countries where freezing temperatures are often combined with outdoor extracurriculars and results in a high “n” for the studies. Outcomes data from many of the expert centers in this area show major benefits of ECMO, including one showing survival post-arrest in nearly 60% of patients and, even more importantly, good neurologic outcomes in 38% compared to only 3% in those without extracorporeal rewarming!
Unfortunately, not all EM physicians will have quick or 24/7 availability of ECMO. While this should be the preferred means of rewarming if available, there are alternatives if it is not. Hemodialysis circuits can also be used to actively rewarm a patient. Generally these can achieve 2-4 degrees/hr of rewarming compared to the 4-6 degrees/hr of ECMO. Thoracic (bilateral chest tubes), gastric (NG tube), and bladder lavage (foley) with warm fluids can also provide several degrees per hour of rewarming if used appropriately. Use a ventilator that can warm and humidify air. Don’t forget about minimizing heat loss by fully drying the patient and keeping as much of them covered as possible.
Lastly, I want to say a word about prognostication. While the mantra is, “you’re not dead until you’re warm and dead”, you can imagine that these patients require a considerable amount of time, effort, and mobilization of resources when they present to the ED. There is information that can help guide which patients are likely to benefit from such aggressive care from those who are, unfortunately, unlikely to be resuscitated. While multiple markers have been studied, the one with the most evidence supporting it, is a potassium value. This value can serve as a sort of surrogate for “warm ischemia time”, or in other words, how long were they warm and dead. This should be obtained and sent early in the resuscitation of the patient. If the value is >12, there is nearly no chance of any meaningful recovery (still very unlikely at >10, and even a cutoff of >8). Conversely, if the potassium level is less than the 8-12 range, the patient still has a good chance at a meaningful recovery if resuscitated to ROSC and these are the patients that should receive everything we have to rapidly and efficiently rewarm them (they are also the patients that can have meaningful recoveries despite impressive downtimes of even hours).
Additionally, historical factors surrounding the hypothermia, if known, can provide valuable prognostic information. Immersion vs. Submersion, which you define in your algorithm, is one example that might influence your decision about whether a patient might have benefit from mobilizing ECMO or other aggressive/invasive rewarming.
Kory Gebhardt, MD
Kaiser Permanente Emergency Medicine
How to cite this post
[Peer-Reviewed, Web Publication] Neil L, Rueter Q (2018, June 4 ). Approach to Hypothermic Resuscitation. [NUEM Blog. Expert Commentary by Gebhardt K]. Retrieved from http://www.nuemblog.com/blog/hypothermia