The Harmful Rush To Hypothermia

Mild hypothermia seems to be a clinically useful therapeutic modality for improving neurologic outcomes following return of spontaneous circulation in cardiac arrest.

However, like any emerging therapy, the precise details regarding which patients are most likely to benefit and how to best apply it are still in flux.  This is an Italian registry study that gathered prospective data on all individuals at 17 hospitals who underwent therapeutic hypothermia following cardiac arrest.  The specific question asked by these authors is regarding the optimal time for initiation of hypothermia – using 2 hours after ROSC as their cut-off.

Turns out, they found an association between “early” (< 2 hours to initiation) therapeutic hypothermia and worsened mortality – 47% mortality vs. 23% mortality in the ICU.  This ~20% absolute difference in outcomes holds up over the 6 month follow-up period.  No difference in cerebral performance category is observed between the two groups, although there is a nonsignificant trend towards better CPC in the “early” group.

Hard to know what to actually do with data.  Is early hypothermia truly harmful?  Because of the observational design, it’s hard to say whether there aren’t confounding baseline differences in the “late” population that produces selection bias for higher survival rates.  Or, are the mortality rates higher in the early group because patients are incompletely resuscitated before initiating hypothermia?

More questions, no answers.

“Early- versus late-initiation of therapeutic hypothermia after cardiac arrest: Preliminary observations from the experience of 17 Italian intensive care units”

2 thoughts on “The Harmful Rush To Hypothermia”

  1. I haven't had a chance to get my hands on the full paper yet so this is just conjecture, but I'm wondering how much a survival bias played into the results. Obviously, in order to have hypothermia initiated later, the patients had to survive longer in the >2 hr group.
    On the other hand, I've been very cautious about the idea of prehospital initiation of hypothermia. There is minimal data supporting the practice, and at this point it's definitely not clear that it is worth throwing a ton of money into purchasing refrigerators or special cooling devices for ambulances, in addition to the cost of training personnel in the practice. At least this study may caution such an approach until there is better data that early hypothermia is really a worthwhile investment.

  2. I haven't had a chance to get my hands on the full paper yet so this is just conjecture, but I'm wondering how much a survival bias played into the results. Obviously, in order to have hypothermia initiated later, the patients had to survive longer in the >2 hr group.
    On the other hand, I've been very cautious about the idea of prehospital initiation of hypothermia. There is minimal data supporting the practice, and at this point it's definitely not clear that it is worth throwing a ton of money into purchasing refrigerators or special cooling devices for ambulances, in addition to the cost of training personnel in the practice. At least this study may caution such an approach until there is better data that early hypothermia is really a worthwhile investment.

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