AHA: Wider Temperature Management Range Okay in Cardiac Arrest Care

In a shift from prior guidelines and two decades’ worth of practice, a new scientific statement from the American Heart Association (AHA) suggests that for comatose survivors of cardiac arrest in whom a cardiac cause is known or suspected, merely keeping body temperatures below 37.5°C—rather than cooling more aggressively—is a “reasonable” strategy for neuroprotection.

That advice is a stopgap, intended to offer expert insight ahead of a formal guideline update due out next year. The move was prompted by the results of the large, randomized TTM2 trial, released in 2021. That study showed no benefit of therapeutic hypothermia for comatose patients with out-of-hospital cardiac arrest (OHCA) caused by a cardiac or unknown event, as compared with patients who were simply kept from developing a fever.

As reported by TCTMD, the TTM2 investigators believe their results challenge the decades-long practice of therapeutic hypothermia, which became the gold standard based on smaller studies published back in the early 2000s. Notably, the current AHA guidelines for cardiopulmonary resuscitation and emergency cardiovascular care, published in 2020, endorse temperature management in unresponsive cardiac arrest between 32°C and 36°C for 24 hours.

TTM, CAPITAL-CHILL, and most recently TTM2 all found no differences in various measures of survival, neurological function, and quality of life if patient core temperature was lowered versus no hypothermic strategy used.

In the wake of TTM2, the International Liaison Committee on Resuscitation (ILCOR) has issued a new consensus opinion that “controlling temperature continues to be important, recommending active fever prevention targeting < 37.5°C for most patients,” with both the European Resuscitation Council and the European Society of Intensive Care Medicine making similar statements.

To TCTMD, lead author Sarah M. Perman, MD (Yale University, New Haven, CT), clarified that the AHA statement, published this week in Circulation, should not be interpreted to mean that centers should stop using therapeutic hypothermia but rather “to widen the opportunity for temperature control.” More detailed guidance will be set out in the 2024 American Heart Association Focused Update on Advanced Cardiovascular Life Support (ALS).

“The purpose of releasing this interim guidance after TTM2 and the ILCOR statement, but prior to the ALS update was to address the variability in the cardiac arrest population and to encourage ongoing aggressive post-cardiac arrest care,” Perman said in an email.  “Yes, there is data that patients with cardiac arrest similar to those included in the TTM2 trial experience similar results with fever control when compared to therapeutic hypothermia, but there are patients, termed ‘special populations’ by ILCOR that were not included in those trials so we are not certain which is the optimal temperature for these populations. Our guidance is intended to open more opportunities for patient-centered therapies.”

In the United States, Perman noted, a significant proportion of OHCA patients have noncardiac etiology, rates of bystander CPR are low, and rates of brain/end-organ injury after cardiac arrest are significant. These patients were not studied in TTM2, she stressed, and represent a group in whom the ideal approach to temperature management for neuroprotection is unclear.

As such, “this statement is not intended to encourage de-implementation of temperature control, but to provide a commentary on temperature selection in varying populations based on the recent data,” Perman said.