Changing target temperature from 33 to 36 in the ICU management of OHCA: a before and after study

I’ve always been skeptical of the original studies claiming efficacy of therapeutic hypothermia for out-of-hospital cardiac arrest (OHCA).

Two small studies published in 2002 demonstrated a profound treatment effect that caused most of the world to change practice.

Anytime you see a small RCT claiming results that are too good to be true, you need to think that the results are exactly that. Medical reversal is common and much of what is published in the medical literature turns out to be wrong.

Along came Nielsen’s study of Targeted Temperature Management (TTM) in 2013 and most of us reversed back to normothermia. However, several studies have indicated that it is difficult to keep patients at this warmer temperature and there are concerns about fever & possible worse outcomes.

   

The Alfred Hospital in Melbourne conducted a retrospective before and after study after they changed their targeted temperature from 33 to 36 degrees. They describe their experience and try to compare outcomes.

Over a 30-month period they had 76 patients with OHCA due to ventricular fibrillation. There were 24 in the before group and 52 in the after.

After the TTM change, less patients got active cooling (100% vs. 70%), less time was spent at the target temperature (87% vs. 50%) and fever rates went up from zero to 19%.

The authors compare the before and after outcomes and state there was a trend towards better outcomes with the before group.

Fortunately, the conclusion in the manuscript is appropriately measured:

After the change from a TTM target of 33 to 36 we report low compliance with target temperature, higher rates of fever, and a trend towards clinical worsening in patient outcomes. Hospitals adopting the 36 target temperature need to be aware that this target may not be easy to achieve and requires adequate sedation and muscle relaxant to avoid fever.

I would go a step further.

A small retrospective before and after study can be rather problematic. With such small numbers it is very likely the groups were different; akin to comparing apples to oranges. No amount of adjustment for confounding factors will fix this.

So, I don’t think we should be taking anything away from the trend toward benefit. Much better-quality evidence from the TTM trial shows there is none.

There are also some potential harms noted in this study. They note patients in the 33 degree arm were intubated a full day longer, experienced more shivering, bleeding requiring transfusion and pneumonia.

What’s the take home message?

Overall this was a small study in a single centre that is poor quality evidence to inform practice. It demonstrates it is more difficult to keep patients at a higher target temperature. Whether this has any impact on real patient outcomes is not known but I think unlikely.

Covering:

Bray J, Stub D, Bloom JE, et al. Changing target temperature from 33 to 36 degrees in the ICU management of out-of-hospital cardiac arrest: A before and after study. Resus 2017;113:39-43. [link to article]