COMMENTARY

The Winding Road That Leads to Optimal Temperature Management After Cardiac Arrest

Aaron B. Holley, MD

Disclosures

September 29, 2022

In 2002, two landmark trials found that targeted temperature management (TTM) after out-of-hospital cardiac arrest led to improvements in neurologic outcomes. The larger of the two trials found a reduction in mortality. Such treatment benefits are hard to come by in critical care in general and in out-of-hospital cardiac arrest in particular. With the therapeutic overconfidence typical of our profession, my institution embraced TTM quickly and completely soon after these trials were published. Remember, this was "back in the day" when sepsis management included drotrecogin alfa, Cortrosyn stim tests, tight glucose control (90-120 mg/dL), and horrible over-resuscitation via the early goal-directed therapy paradigm.

If you've been practicing critical care medicine for more than a few years, you already know where I'm going. Most of the interventions in the preceding paragraph were adopted but discarded before 2010. Though TTM has managed to stand the test of time, our confidence in its benefit has waned since 2002. Hypothermia — temperature management with a goal of 32-36 °C — has been struggling to stay relevant ever since the publication of the TTM randomized controlled trial (RCT) in 2013. Then came the HYPERION trial, which brought the 32-36 °C target back from the dead (pun definitely intended) in 2019. This is critical care medicine: Today's life-saving intervention proves harmful tomorrow, but withholding it may constitute malpractice a few months down the road.

So where are we now? Good question. I've had seasoned neurointensivists insist that 33 °C remains the standard of care and others who've endorsed normothermia. So much for finding an answer via my more specialized colleagues.

Let's go to the guidelines then. Prompted largely by HYPERION, a temperature target of 32-36 °C was endorsed in 2020 and 2021. Then came publication of the TTM2 trial, the largest temperature management RCT to date, which found no benefit to targeting 33 °C. A network meta-analysis published in 2021 reached a similar conclusion. A recently released update by the same international guideline group now recommends targeting normothermia (< 37.7 °C) and avoiding fever, and it specifically says that there is insufficient evidence to support a 32-36 °C target. Okay, everyone tracking all that?

Lest I sound overly catty and nihilistic, I see all this in a positive light. Huge credit goes to the critical care medicine academic community for putting together so many RCTs. The scientific reality is that it takes "a lotta" sample size to clarify the effects of an intervention. Throw in the inevitable bevy of confounders (in- vs out-of-hospital cardiac arrest, resuscitation time, initial rhythm, and so on), and you get a feel for the work required to understand a treatment's true effects.

Advances in guideline science and the hard, often unpaid work of panels are also important. The guideline panel I've been citing came out for aggressive temperature control (32-36 °C) a few months before the TTM2 RCT was published. In the past, they updated their recommendations every 5 years, but this time, they were out with a new manuscript that incorporated TTM2 in less than a year. If you've been involved at any level with producing guidelines, you can appreciate this achievement. Assuming that aggressive hypothermia is truly harmful, waiting 5 years to incorporate TTM2 could have led to significant morbidity.

I do take issue with you early adopters, though. Given the litany of failed therapies that have shown initial promise, and the well-documented human tendency to underestimate the impact of sample size, your rapid implementation of major interventions is puzzling. One might think you'd learned your lessons after seeing drotrecogin alfa, Cortrosyn stim tests, tight glucose control, early goal-directed therapy, and aggressive TTM come and go. Your recent enthusiasm for vitamin C after publication of a single before-after study suggests that you haven't.

Aaron B. Holley, MD, is an associate professor of medicine at Uniformed Services University and program director of pulmonary and critical care medicine at Walter Reed National Military Medical Center. He covers a wide range of topics in pulmonary, critical care, and sleep medicine.

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