Cooling And Cardiac Arrest

Posted by Jeremy Windsor on Oct 23, 2020

Last year we highlighted the results of PARAMEDIC2 study. There's no denying that they made for a very sobering read. Amongst those studied, less than 5% survived an out of hospital cardiac arrest (OOHCA) and importantly, many of those who made it to discharge were crippled with life changing neurological injuries. Clearly, we have a long way to go to improve outcomes in OOHCA and every step in the process - from immediate care to rehabilitation - warrants further scrutiny...

For several years the role of cooling following cardiac arrest has been widely debated. Whilst there's now growing agreement on cooling those with a shockable rhythm, its role in patients presenting in asystole or pulseless electrical activity is less clear. In this post we'll take a look at a recently published study in the New England Journal of Medicine of 581 patients with a non-shockable rhythm who were randomised into 2 groups and cooled for 48 hours following cardiac arrest. The "Hypothermia" (H) group were cooled to 33 (+/-0.5) degrees C for 24 hours and then warmed slowly over the following 24 hours to a temperature of between 36.5 and 37.5 degrees C. Meanwhile, the "Normothermia" (N) group were cooled to between 36.5 and 37.5 degrees C for the full 48 hours. 

At this point it's important to note that this population were chosen with a great deal of care - rather than include everyone with a cardiac arrest, only those adults found to have a non-shockable rhythm, a time to CPR of 10 minutes or less and a spontaneous circulation within 1 hour were included. Therefore extrapolating the following results and conclusions to other patient groups should be done with the utmost caution!

The Blanketrol 3 System is a commonly used device that can rapidly control core temperature

Neurological outcome at Day 90 was the primary outcome in this study and was measured using the Cerebral Performance Category (CPC). The CPC is scored between 1 (conscious, alert and able to work) and 5 (brain death). At 90 days, significantly more patients had a CPC score of 1 or 2 in the H group (29 - 10.2%) than in the N group (17 - 5.7%).

In addition to neurological status, a number of secondary outcomes were also measured. Unfortunately, these did not differ between the 2 groups. Irrespective of treatment, patients spent a similar duration in ITU and more than 80% died within 90 days.

Despite having no impact upon mortality, this study shows that cooling to 33 degrees C for the first 24 hours after OOHCA improves neurological outcome. These improvements were not dramatic. After all, both groups had a similar numbers of survivors who scored a CPC of 5. Nevertheless, the effect was clinically significant. A close look at the data shows that this degree and duration of cooling "shifted" patients from scores of 3 and 4 towards 1 and 2. In reality this means, that there were patients who can attribute something as important as their independence to just a few hours of cooling following a cardiac arrest. Cooling may therefore have a part to play in all OOHCA's. Further research is clearly warranted to match the degree and duration of hypothermia to the patient's clinical background and presentation. We'll keep you posted with what comes next!

Further information about the role of prophylactic antibiotics in OOHCA can be found hereFor more on the impact of hypothermic cardiac arrest see this.

Is there a role for Vitamin D in critical care? Procalcitonin?

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