Is it still cool to cool in cardiac arrest? The new TTM Hypothermia trial! #FOAMed, #FOAMcc

So the other dayI read the TTM trial (http://www.nejm.org/doi/full/10.1056/NEJMoa1310519?query=featured_home#t=article) with great interest, as cardiac arrest and the post-resuscitation phase have always been among my pet topics.

First of all this is a big trial.  Bigger that the previous ones that established hypothermia as a standard of care. Does it obviate those previous results?  Absolutely not. Those trials were not 32/33 vs 36 but 32/33 vs “whatever happens.”

Hypothermia makes a lot of sense physiologically, but of course that doesn’t mean that it might not have some harmful side effects that have not yet been clearly delineated (besides the current known hemodynamic ones and relatively benign electrolyte and renal alterations).

However, it is pretty clear that, compared to 33 degrees, 36 does just as well, which leans towards saying that all we have to do is avoid fever, or stay in a very mild hypothermia.

Avoiding secondary injury in brain pathology is key (no desat, no hypotension, and no fever), and in anoxic encephalopathy, it is no different.  The key thing is that in this trial, the temperature was controlled – ie it would not be acceptable to do no cooling, and just chase the fever (which is very common) with acetaminophen, which would invariably result in significant time spent above 36 (oops, tylenol didn’t really work, ok lets put the blanket, etc …this is gonna be hours).

So is this the end of aggressive cooling?  Not necessarily.

For anyone interested in the topic, I suggest reviewing Peter Safar‘s data on dogs and cold aortic flushes – it is absolutely unbelievable to see dogs who  had an arrest, got the cold aortic flush (brain temp below 10 degrees), are left stone cold dead for 45 minutes, then resuscitated and are then able to go around a few days later and do doggie things like run and bark and eat…  So I don’t think that cooler isn’t necessarily better, but that we haven’t yet delineated what are the pros and cons of each temperature range or how to get there practically and safely.

So what should we do?  Well, it would seem reasonable to do either at this point, and accepting a temp between 32-36 (I have usually preferred 33-34 as they rarely drift down into the 20’s as I’ve seen the 32’s do) as being adequate. This may make hemodynamics a bit easier to manage in certain cases.
Also check out Scott’s take at:
 http://emcrit.org/podcasts/emcrit-wee-targeted-temperature-trial-changes-everything/#comment-58635
And the RAGE Podcast addresses this topic at about 25 minutes:
…and of course, keep abreast of further data and subgrouping that may become available on this, and further trials. But for now, its definitely still cool to cool, maybe just a little less…

3 thoughts on “Is it still cool to cool in cardiac arrest? The new TTM Hypothermia trial! #FOAMed, #FOAMcc

  1. May be it should now be called rather: ‘Therapeutic Normothermia’? 😉

    Marco.

  2. Philippe St-Arnaud

    Quick thoughts :

    1-The population studied was different (not only shockable rhythms). The likelyhood of finding a difference was hence lower.
    2- They wanted to reach a 20% difference in mortality. They were expecting a lot… I think the likelyhood of a positive finding was very low. This was not a non-inferiority designed study.
    3- The primary outcome was survival (not neuro intact discharge). Maybe they could have find a difference favoring the 32-34 if neuro intact would have been the primary outcome?

    Because of these 3 points, It seems that the chances of this study to find a difference favoring the 32-34 were very low.

    I am also concerned that hypothermia will be thrown away a little too quick, considering that the study was published in such a journal…

    Thanx for the great posts!

    Philippe St-Arnaud

    • Great comments Philippe,

      Definitely agree with your thoughts, all very valid points. Indeed I worry that people’s initial reaction (which I have seen firsthand in our ED as well as one in Toronto) is to say “oh good we don’t have to cool!” which, sadly, is far off the mark, since 36 is not normothermia. Hopefully each institution will have some key physicians such as yourself able to dissect key elements and realize that the new hypothermia range has simply expanded.

      thanks for reading!

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