Commentary: It’s Time to Deep Freeze Hypothermia After Cardiac Arrest

Suffering a cardiac arrest out of the hospital portends poorly. The topic frustrated researchers for decades in their search for something to improve the abysmal outcomes. Early defibrillation for pulseless ventricular tachycardia or ventricular fibrillation made a dent in the mortality rate, but few other interventions showed promise.

 

In the early 2000s two small studies, one from Australia (Bernard et al; 2002) and one from Europe (The Hypothermia After Cardiac Arrest Study Group; 2002), seemed to offer a glimmer of hope that cooling patients who remained comatose after return of spontaneous circulation (ROSC) would result in not only improved survival, but improved survival with good neurologic outcomes.

 

Despite grumblings that these studies were tiny and deeply flawed, this concept got integrated into virtually every resuscitation guideline. Emergency departments and hospitals worldwide stocked cooling gadgets and anointed patients with bags of ice on necks, groins, and armpits in an attempt to salvage as many neurons as possible in these patients, dutifully following said guidelines.

 

The grumblings grew louder as subsequent studies were unable to duplicate the results of those first two. A study of 950 randomized patients published in 2013 (Nielsen et al; 2013) showed no significant difference in outcomes in patients cooled to 33°C versus those with “enforced normothermia” to 36°C. Despite the fact that the total number of patients in this study was significantly higher than in those first two combined, the practice remains cemented in resuscitation guidelines calling for cooling the patient to 32 to 36°C “as soon as possible” and maintaining that temperature for at least 24 hours.

 

Undaunted, the targeted temperature management (TTM) researchers who published the 2013 study did a larger study (Dankiewicz et al; 2021), published in the June 17, 2021, issue of the New England Journal of Medicine. Dankeiwicz et al enrolled 1900 comatose adults after out-of-hospital cardiac arrest (OOHCA) and randomized them to either targeted hypothermia to 33°C or normothermia (body temperature ≥ 37.8°C) with early treatment of fever. There was no significant difference in death or functional outcome at 6 months. In addition to no improved outcomes, the study showed some harm (more unstable dysrhythmias, longer time on a ventilator) than the normothermia group.

 

So, what now? The two studies by the TTM researchers done eight years apart show no benefit and imply possible harm from making post-arrest patients hypothermic. It seems that keeping a patient normothermic (ie, not letting them develop a fever) should be the focus at this point. Time to change those guidelines.

 

References

Bernard SA, Gray TW, Buist MD, et al: Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia. New Engl J Med 346:557-563, 2002. Doi: 10.1056/NEJMoa003289

The Hypothermia After Cardiac Arrest Study Group: Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. New Engl J Med 346:549-556, 2002. Doi: 10.1056/NEJMoa012689

Nielsen N, Wetterslev J, Cronberg T, et al: Targeted temperature management at 33°C vs 36°C after cardiac arrest. New Engl J Med 369:2197-2206, 2013. Doi: 10.1056/NEJMoa1310519

Dankiewicz J, Cronberg T, Lilja G, et al: Hypothermia vs. normothermia after out-of-hospital cardiac arrest. New Engl J Med 384:2283-2294, 2021. Doi: 10.1056/NEJMoa2100591