Hot Evidence Debate in Hypothermia

Did you know that a style of yoga is practised in a room at 40°C (104°F) with 40-50% humidity for 90 minutes? If you did not know this, and you are surprised or even shocked to hear about Hot Yoga for the first time, you have the same reaction as I did when I learned a few years ago that many controversies existed regarding therapeutic hypothermia after cardiac arrest.

Fifteen years ago, when I started my residency, after a cardiac arrest event in the hospital, my attendings never used any means to lower the body temperature of a patient, nor was there a hypothermia protocol. Among the steps to follow after a cardiac arrest call, hypothermia was never mentioned, or at least I don’t remember it. I also did not think about the clinical guidelines or who made the recommendations at that time. In my view, the workplace in which one is trained and where one will later work greatly influences the performance of an individual’s career. In addition, when I moved to Paris to start a fellowship, no one in my new hospital made any reference to hypothermia after cardiac arrest. So what I witnessed there was confirming what I really already knew: hypothermia was not a thing! This example, and many others, is why case reports, or individual experiences in medicine, are not used in clinical practice, though they can have a place to start new inspiring ideas.

After listening to the Hot Evidence Debate on hypothermia for the first time, I simultaneously followed all the aspects related to hypothermia after cardiac arrest from the authors of the main papers in the field. They answered questions simultaneously from all angles to deepen and clarify why the ERC-ESICM-Ilcor, Cochrane, and ESAIC-EuSEM had reached divergent conclusions.

In fact, in this case, as in many others in medicine where the evidence is very low, different people judged the benefits or side effects of a certain intervention differently. While evaluating the quality of medical evidence is intended to be transparent, coherent and reproducible, assessing benefits and risks is subjective and may vary from individual to individual. And it is precisely in these cases where the evidence is scarce that the human factor plays a stronger role. This is why we could read recommendations for or against an intervention (in this case, hypothermia) when the quality of the evidence is very low, which means that, as the outcome is uncertain, I may judge whether it is justified to perform such an intervention or decline to do it.

And, of course, whether a physician recommends an intervention when the level of evidence is very low will depend to a large extent on the habits and routines that the physician has already. It would be unlikely that I would advise such an intervention if I do not normally use therapeutic hypothermia after cardiac arrest, right? Furthermore, even if I would like to recommend it if nobody in my hospital uses it and if no one is used to it, and hypothermia is considered a novel approach, I would not be able to implement it either since treatment administration and maintenance depend on several individuals over time.

I wonder what is the proportion of authors in the different documents that use therapeutic hypothermia regularly. I could almost imagine that both the authors of the ESAIC/EuSEM statement and the Cochrane systematic review use hypothermia after cardiac arrest for the most part. Most of the authors of the ERC/ESICM clinical guidelines do not use hypothermia regularly, which evidently makes them recommend hypothermia less. This circumstance is, according to the definitions of evidence-based science, a clinical conflict of interest, i.e., you do not have an economic conflict of interest, but you do have a clinical conflict of interest towards the intervention you are evaluating. The interventions that are more unfamiliar or infrequent to a person are more likely to be discarded, and that is called familiarity bias, a phenomenon studied mainly in investors that tend to choose stocks based on a preference for familiar or easily recognizable investments despite having other options available.

My personal conviction is that our role of serving and caring for patients should be above our own interests and beliefs. In essence, each new study has to achieve to confirm or refute a hypothesis and not to “prove us right”. The scientific method has important limitations, mainly arising from the complexity of analyzing with Cartesian mathematics all the interconnected variables of the human body and its processes. In the case of hypothermia, we have all observed how applying local cold to a bone fracture, or when we have had a contusion, the inflammation decreases over time. However, could we say that cooling down a patient can also produce less brain damage after a cardiac arrest? From the observation of natural phenomena, I wonder, does heat not help to reduce the viscosity of fluids and help the blood to circulate more easily in the body after an event of cardiac arrest? Furthermore, if colds can be beneficial in reducing brain injury, shouldn’t we also start using them in traumatic brain injury cases?

Following the debate, I still have many questions and doubts, possibly because I am not an expert in this area. I suspect these questions will disappear as new studies with a robust methodology are available. I find, in general, that the evaluation of hypothermia, or specifically of a therapeutic hypothermia profile, is really very challenging as it depends on how long it takes to establish hypothermia, what methods we use to maintain hypothermia, what equipment we use to monitor hypothermia and how long we maintain it after cardiac arrest, or even how long the patient remains in cardiac arrest – can we say that after 10 minutes of an episode of cardiac arrest without returning to spontaneous circulations hypothermia will no longer be effective? I deeply admire the people conducting research in this field for the abovementioned problems.

In particular, I would like to thank the three speakers, Jerry Nolan, Jasmin Arrich and Bernd Böttiger, for their great communication skills and for accepting the invitation to participate in this webinar. There are few opportunities to contrast different approaches in such a pleasant and healthy environment, putting oneself in the shoes of the other and understanding the tremendous amount of work it has taken to come to these conclusions. In parallel, we have been extremely pleased that this format was very well received by the other authors of these documents who, for practical reasons, have not joined us, such as Lars Andersen and Jasmeet Soar of the ERC-ESICM-Ilcor guidelines, with whom we are now collaboration in a new clinical guideline, Harald Herkner from Cochrane, with whom I had the opportunity to speak in person this September at the Global Evidence Summit in Prague, and last but not least with Wilhelm Behringer and Athanasios Chalkias from the ESAIC/EuSEM statement, one of whom was part of the ESAIC guidelines committee until a few months ago.

To know all the evidence from the authors in-depth, I recommend you listen to the debate and hear the latest studies and their limitations in their own words. If, in your opinion, hypothermia is an effective treatment after cardiac arrest that may improve the neurological prognosis while offering minimal side effects, I invite you to try a Hot Yoga class that will surely serve to stretch and relax your muscles in depth after a long day in the hospital.

Author

•  Dr. Carolina Soledad Romero García