Lessons From the Resuscitation Sessions at AHA

Lance B. Becker, MD; Graham Nichol, MD, MPH


January 23, 2014

In This Article

Cooling to 33°C vs 36°C

Dr. Becker: Let's talk about that one for a moment. There was the TTM study that came out of Europe that compared the use of 2 different temperature management systems.[4]

What they did is they took patients after cardiac arrest and after they had arrived at the hospital, and they cooled them to 2 different temperatures: One was 33°C, which is what most hospitals do, and another group was 36°C. They maintained that cooling for approximately 24 hours and slowly rewarmed those patients, and they came to a surprising conclusion: There appeared to be no difference between those 2 therapies for the inpatients that they studied in this cohort, and it was a decent sample size.

Dr. Nichol: Were you surprised by the result?

Dr. Becker: I was a little surprised by the result, and I'm at the point where I really am reconsidering some of my own practices and trying to understand what it might mean. I'm curious about whether you have thoughts, because I have a lot of thoughts on what it may mean for us.

Dr. Nichol: I have a lot of questions; I don't necessarily have answers. There were 2 other studies published more than 10 years ago that showed that compared with no cooling, cooling was beneficial when applied in hospital to patients who'd been resuscitated.[5,6] I think some were surprised by the results of the Swedish study, but neither group in this recent study went without cooling.

Dr. Becker: Yes, that's an important point to note -- that both groups were cooled. It was simply a difference of degree. To maintain a patient's temperature at 36°C turns out to be a lot of energetic work -- meaning that when you look at just the physical number of calories that you need to extract out of a person to keep their temperature at 36°C, which we think of as (relatively) normal, it turns out that energetically, it's a lot of work to do that. It's not a case of just doing nothing to the patient and considering them to be normal, and I think that that's a big difference between not doing anything.

Dr. Nichol: I agree, and I think we should not stop caring for these patients. We should continue to care for them. We may need to individualize the dose of hypothermia, because it may be that patients who have had a longer downtime need more hypothermia.

Dr. Becker: I think one of the things that would explain these findings is if it turns out (as I somewhat believe) that there are different levels of injury. There are probably some patients who do well with 36°C and some who will do well with 33°C, and if you do a randomized study where you mix all those patients up and you don't have a way to sort that out in terms of which therapy the patient actually needs, you come out with a negative study almost every time. It seems to me that it's very likely that this is now going to push us to do some more research to do more studies and perhaps to identify which patients require which form of therapy.

Dr. Graham: Sure, and as we care for our patients on a day-by-day basis, we need to assure the quality of the care that we provide and make sure that we're not allowing patients to develop a fever, because I think all of these studies would suggest that fever or no cooling is harmful.

I think there may also be questions about whether earlier initiation of cooling in hospital is beneficial, and whether more rapid cooling may be beneficial. It appeared to me that in the study that was presented yesterday, they didn't achieve a target temperature for 8 hours, which is a relatively long time in this population.

Dr. Becker: And you would think in general, it would be easier to cool someone to 36°C, which most of us consider a normal temperature. The fact that it took 8 hours to achieve that demonstrates to me the energy that it took. If we could look at however they cooled those patients down (with a device or saline or whatever), they were doing a lot to that patient to achieve that 36°C.


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