Longer-duration cooling of people in coma after cardiac arrest may have limited or no benefits

Therapy Breakthroughs 4. dec 2022 3 min Consultant Christian Hassager Written by Kristian Sjøgren

Preventing fever by cooling people who experience cardiac arrest and end up in a coma has been standard practice worldwide for nearly two decades. Now new research is challenging this approach by showing that targeted temperature management for 72 hours does not actually benefit them. Cooling for 36 hours is sufficient, and temperature management may have no benefits at all.

For nearly two decades, the standard procedure in intensive care units globally for people collapsing with severe cardiac arrest has been to maintain coma and cool their body for 72 hours.

The purpose is to protect the brain from damage, similar to the fact that people who have a cardiac arrest in cold water can survive longer and can recover without brain damage because the body and brain have been cooled down.

Nevertheless, new research shows that cooling people in a coma after cardiac arrest may not be that beneficial – at least not maintaining the cooling for 72 hours.

The researchers and doctors randomised participants to either 36 hours or 72 hours, and this gave the same results in survival and risk of serious brain damage.

The research results have the potential to change the international guidelines.

“In 2002, some studies showed that cooling may be beneficial, and this has since been implemented in international guidelines. But we have neglected to investigate how long we need to maintain the cooling and whether the effect is really as good as the research revealed then. Our study elucidates this,” explains a researcher involved in the study, Christian Hassager, Consultant, Department of Cardiology, Rigshospitalet and Professor of Critical Care, University of Copenhagen.

The research, which has been published in the New England Journal of Medicine, is the research group’s third consecutive article in this prestigious journal on approaches to critical care after out-of-hospital cardiac arrest.

Effective if fever is controlled

Christian Hassager has previously investigated the effect of cooling people who are in a coma after cardiac arrest.

This research showed that their body temperature does not need to be reduced as much as previously.

When cooling was implemented in the intensive care units globally, the target temperature was 33°C, but Christian Hassager’s research showed that cooling to 36°C is just as effective.

This cumulative research has resulted in the international guidelines now recommending that body temperatures be reduced to 36–37°C for 24 hours and then fever prevention be maintained for a further 48 hours.

The new research results challenge this approach.

Cooling for half as long

Researchers and doctors from Rigshospitalet in Copenhagen and Odense University Hospital randomised 789 patients following cardiac arrest to either be cooled to 36°C for 24 hours and then kept fever-free for a further 48 hours (total 72 hours) or to be cooled to 36°C degrees for 24 hours and then kept fever-free for a further 12 hours (total 36 hours).

During the follow-up period, the researchers investigated whether the two approaches differed in the risk of death and severe brain damage.

All participants were adults, non-pregnant, had collapsed with out-of-hospital cardiac arrest and were in a coma when they arrived at the hospital. Christian Hassager describes these people as severely ill.

“Previously, we could not do much for these people and often just let them die. But with cooling, we started to think that we could do something, and this led to a wave of new measures that today have increased the chances of survival and of survival without serious brain damage. Now we just have to figure out what actually works and what does not,” says Christian Hassager.

Shorter cooling just as beneficial

The results show that keeping patients fever-free for 36 hours or 72 hours makes no difference. Survival and the proportion experiencing brain damage were similar in the two groups.

In the 36-hour group, 32% of the patients cooled for 36 hours versus 33% of those cooled for 72 hours experienced a primary end-point event of death or brain damage.

A few more patients cooled for 36 hours developed fever, but this did not appear to harm them.

“Cooling for 36 hours seems to be just as effective as cooling for 72 hours. We should therefore not waste time and resources reducing their temperature for 72 hours after cardiac arrest,” explains Christian Hassager.

Temperature reduction may have no benefit

Christian Hassager says that the study will not lead to measures that improve survival or reduce the risk of developing brain damage.

However, hospital intensive care units can save time and money.

Some hospitals today have special cooling suits , and others insert a cooling element into a vein in the neck. Both can be implemented for 36 hours instead of 72 hours without changing the outcome.

“In a wider context, taking patients out of the refrigerator or taking the refrigerator out of them makes sense, and we will also do this in the future when, presumably, the guidelines in Denmark change based on our results,” says Christian Hassager.

He elaborates that the study should also be just one of several to elucidate how well cooling after cardiac arrest works or whether it has any benefit at all.

“We would like to investigate this. I think that the benefit is not at all what was found in 2002. This should be investigated in a large randomised study, which we would like to lead ourselves. I think that in a decade we may have completely abandoned reducing the body temperature of most of our patients in a coma,” concludes Christian Hassager.

Duration of device-based fever prevention after cardiac arrest” has been published in the New England Journal of Medicine. In 2020, the Novo Nordisk Foundation awarded a grant to Christian Hassager for the project Steroid Treatment as Anti-inflammatory and Neuroprotective Agent Following Out-of-hospital Cardiac Arrest: A Randomized Trial.

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