HWN Suggests

Giving Hypothermia the Cold Shoulder

The utility of hypothermia following ischemic insult seems biologically plausible, but... perhaps it’s not so much hypothermia as the maintenance of normothermia. Already part of modern post-stroke care, treating and preventing fever improves outcomes – it may simply be the observed benefits are due to intensive antipyresis, rather than hypothermia.

It seems still reasonable to use gentle cooling as a prophylaxis against hyperthermia, but more importantly, it is time, yet again, to reflect on how better evidence refines established practice. Without continuing to recognize the limitations of our knowledge, we must caution ourselves against rushing to generalize implementation from…

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 Data Supporting Therapeutic Hypothermia for Cardiac Arrest Aren’t So Hot

We are nearly back at square one with respect to therapeutic hypothermia. Certainly, the routine use of therapeutic hypothermia under current protocols has little remaining justification. It would likewise be reasonable to discontinue routine use of active temperature management devices while awaiting further evidence of benefit. While the trends in medicine always tend to favor adoption rather than de-adoption of new practices, the time has likely come to fully reevaluate any role for therapeutic hypothermia.

 History: Therapeutic Hypothermia

As for the temperature. 36 degrees C has support for the new standard. With increasing NNT, there may be benefit to going lower but with diminishing returns in return for more adverse events.

 The big chill on ‘therapeutic’ hypothermia

Despite ‘therapeutic’ hypothermia’s widespread use, the evidence for the practice has always been weak.

 Therapeutic Hypothermia After Cardiac Arrest – Mixed Evidence

But as science does with everything, evidence comes along and changes things. The famous TTM trial was published in 2013. It was a large RCT that showed no difference between a target temperature of 33 degrees and 36 degrees. Even though both groups were technically hypothermic, a few logs were taken off the fire of therapeutic hypothermia, and it was no longer considered “the standard”. This year, an even bigger RCT was published, the TTM2 trial, and we now have new guidelines from ILCOR. You would expect that we would have a clear answer after 5000 years of experimenting with therapeutic hypothermia on whether or not to cool patients after cardiac arrest. Well, not so clear.

Articles of Interest

A-Contemporary-Update-on-Targeted-Temperature-Management

Although, targeted temperature management is strongly recommended for neuroprotection in patients who remain comatose after resuscitation from a cardiac arrest, this recommendation is based on weak evidence of benefit, mostly from earlier trials that had many limitations.

Does Targeted Temperature Management Actually Work?

The current optimal temperature remains elusive, but what is certain is that the prevention of fever is paramount.

Hypothermia for neuroprotection in adults after cardiac arrest

Cooling the body after successful resuscitation may reduce the risk of brain damage and improve neurological outcomes. When we compared people whose bodies were cooled to 32 °C to 34 °C after resuscitation versus those whose bodies were not cooled, we found that 532 per 1000 of those receiving cooling would have no, or only minor, brain damage, while only 377 per 1000 not receiving cooling would have no, or only minor, brain damage. Cooling had no effect on survival.

Hypothermia vs Normothermia for Out-of-Hospital Cardiac Arrest

Targeted temperature management may still have a role in post-cardiac arrest therapy as a super aggressive approach to avoiding fever. With no benefit in survival and more harm with adverse events (ie. additional paralytics and prolonged duration of mechanical ventilation), cooling may not have as meaningful of an effect on clinical improvement as originally thought.

No Benefit to Hypothermia Compared with Normothermia After Cardiac Arrest

Protocols that focus on achieving hypothermia (32°C–33°C) confer risk without any clear benefit. Active temperature management with a target of normothermia makes sense and will be my practice moving forward.

Targeted Temperature Management

Targeted Temperature Management (TTM), also referred to as Therapeutic Hypothermia, is the maintenance of specific body temperature goals after return of spontaneous circulation (ROSC) post-cardiac arrest to reduce brain injury.

Targeted temperature management (TTM) after cardiac arrest

Current evidence suggests that normothermia and actively avoiding fever (>37.7oC) has no significant difference in morbidity or mortality (including QoL and functional outcomes) compared with therapeutic hypothermia (of 33oC or 36oC) following CA. However, current professional organisations continue to recommend TTM of 33-36oC for at least 24 hours following cardiac arrest.

What Is the Use of Hypothermia for Neuroprotection After Out-of-Hospital Cardiac Arrest?

IH provides neuroprotection in animal models of cardiac arrest, but is of uncertain benefit in humans. Use of EMS-initiated rapid infusion of cold crystalloid as a means to achieve faster cooling rates after ROSC in patients with and without VF arrest did not improve survival. Whether intra arrest or volume-sparing cooling methods in the field are beneficial remain unclear.

What’s the target temperature for OOHCA cooling. St.Emlyn’s

It’s not for me to tell you what to do really. I like cooling patients, I think it works and there is evidence to support it. As for a target temperature then this trial really gets us thinking. It’s not definitive but there is enough to get us interested in questioning whether a prevention of fever is as important as cooling to hypothermic levels. There may well be no difference, there may be harm, there may even be benefit to a lower cooling temperature I just don’t know and I’m not sure this trial helps us that much.

Resources

The NNT

1 in 6 were helped (neurologically-intact life saved)