Journal Jam 19 Therapeutic Hypothermia After Cardiac Arrest – Mixed Evidence

Therapeutic hypothermia after cardiac arrest is not new. It was a thing 5000 years ago in Egypt. Fast forward to the 20th century and the first clinical trial of therapeutic hypothermia after cardiac arrest in 1958 reported a 50% survival - pretty much the exact same survival rate reported in the recent TTM2 trial. And back in the early 2000’s therapeutic hypothermia was widespread: as soon as we’d achieved ROSC we’d go running for ice packs and cooled crystalloid, and get the ICU on board to set up for their cooling protocol. It was considered "standard of care". We were all convinced that cooling them would not only save their lives but save their brains, so that they could think and talk and walk like they did before the cardiac arrest. The pathophysiology made sense, the main idea being that cerebral blood flow and oxygen consumption decreases, which preserves autoregulation and saves the brain from ischemic insult and edema. 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. In this Journal Jam podcast, special guest Dr. Mizuho Morrison joins Anton and Justin to clear up the muddy waters of therapeutic hypothermia with a deep dive into the world’s literature... Podcast production by Justin Morgenstern and Anton Helman Podcast editing and sound design by Anton Helman. Blog summary by Anton Helman, October 2021. Cite this podcast as: Helman, A. Morgenstern, J. Morrison, M. Journal Jam 19 - Therapeutic Hypothermia after Cardiac Arrest - Mixed Evidence. Emergency Medicine Cases. October, 2021. https://emergencymedicinecases.com/journal-jam-therapeutic-hypothermia-cardiac-arrest. Accessed [date] The original 2 RCTs in 2002 that made therapeutic hyperthermia "standard" The Bernard trial, while showing an impressive improvement in the primary outcome of neurologic function well enough to be sent home or to a rehab facility (49% hypothermia group vs 26% in normothermia group), did not show a mortality benefit and had many weaknesses including: not randomized, selection bias, unblinded and included patients with fever. The HACA RCT showed a 16% difference in 6 month functional neurologic status in the primary outcome (55% vs 39%), and 14% mortality benefit (41% vs 55%). This trial too suffered from selection bias, it was unblinded and included patients with fever. The original TTM trial 2013: no difference between 33 and 36 degrees This was a large RCT in 36 ICUs internationally that showed no difference in the primary outcome of mortality (50% vs 48%) and no difference in neurologic outcomes between cooling patients to 33 vs 36 degrees Celsius. This was a well-done RCT but suffered from very large confidence intervals and did not answer the question of whether cooling is any better than no cooling. Timing of therapeutic hypothermia: prehospital RCTs - is earlier better? 3 pre-hospital RCTs totalling more than 2,000 adult patients showed no significant clinically improved outcomes with therapeutic hypothermia. HYPERION RCT: therapeutic hypothermia in non-shockable rhythms The HYPERION RCT randomized adult patients to 33 degrees Celsius vs 36.5 to 37.5 Celsius for 24 hours and found that survival with a favourable neurologic outcome at 90 days was 1...