Therapeutic hypothermia for in-hospital cardiac arrest? Who knows...?

There is some evidence to suggest that therapeutic hypothermia may (or may not) be efficacious for out-of-hospital cardiac arrest (OHCA). But what about cardiac arrest that happens in the hospital (IHCA)? She we bust out the esky and ice blocks?

These authors sought to answer this question by looking at a large registry of 26,183 patients with IHCA to see who did and didn’t get cooled. The primary outcome was survival to hospital discharge. To be clear, this was an observational study and patients were not randomized.

As you can imagine, there were quite substantial differences amongst the group of patients who were offered cooling and those that did not. So it’s a bit like comparing apples to oranges before we even start with therapeutic hypothermia.  

So how do we try to correct for all of this confounding? Throw in some fancy propensity matching!

After adjustment the therapeutic hypothermia was associated with lower in-hospital survival (27.4% vs. 29.2%). Cooling was also worse for most secondary outcomes.

So therapeutic hypothermia is harmful for IHCA?

Answer: we don’t know.

With all of the inherent limitations of this study design, the results are pretty irrelevant. Registry data is notoriously unreliable. Data is often missing, incomplete or just plain wrong. If you start with rotten eggs, you can’t make a very good Pavlova.

In addition, there is no amount of fancy statistics that can reliably account for all of the confounding. Lots of assumptions go into these “adjustments” and we can only correct for what we know and measure accurately. As Donald Rumsfeld said, “...there are also unknown unknowns.”

What are all the variables that make a patient sicker? Have we measured them accurately and precisely? There’s no way...

In the end, this study suggests there is clinical equipoise and it would be ethical to conduct a randomized clinical trial. Certainly this might give us a better answer... but I wouldn’t hold my breath.

For now, we can save our ice for something that really matters... margaritas anyone?

Covering:

Chan PS, Berg RA, Tang Y, et al. Association Between Therapeutic Hypothermia and Survival After In-Hospital Cardiac Arrest. JAMA 2016;316(13):1375-82.