Despite international recommendations, a low body temperature may not benefit unconscious patients who survive a possibly cardiac-related cardiac arrest outside the hospital setting, according to a study published online Nov. 17 in The New England Journal of Medicine.

The results were presented simultaneously at the American Heart Association’s scientific session in Dallas.

In the Target Temperature Management (TTM) trial, researchers randomly assigned 939 patients in 36 intensive care units (ICUs) in Europe and Australia to targeted temperature management of either 33°C or 36°C. All patients experienced a heart attack outside the hospital and were unconscious as defined by a Glasgow Coma Scale score of less than 8.

The primary outcome was all-cause mortality and the secondary outcome was a composite of death at six months or poor neurologic function, which was evaluated with the Cerebral Performance Category (CPC) scale and a modified version of the Rankin scale.

“We did not find any harm with a targeted temperature of 33° C as compared with 36° C,” wrote the authors, led by Niklas Nielsen, MD, PhD, of Helsingborg Hospital in Helsingborg, Sweden. “However, it is worth recognizing that for all outcomes, none of the point estimates were in the direction of a benefit for the 33°C group.”

In the lower temperature group, 50 percent of the patients died compared with 48 percent of the patients in the higher temperature group (hazard ratio [HR] 1.06). At the six-month follow-up, there were no significant differences between the two groups in terms of the secondary outcome (54 percent in the 33°C group vs. 52 percent in the 36° C group (risk ratio 1.02). Serious adverse events occurred in 93 percent of the 33°C and 90 percent of the 36°C group.

The authors acknowledged that the trial was not fully blinded—staff in the ICUs knew about the targeted temperature. Additionally, some potentially eligible participants were excluded due to the requirement of written consent.

Regardless of the limitations, the authors argued that their study does not suggest any benefit for a body temperature of 33°C in these patients compared with a temperature of 36°C.

“[I]t is important to acknowledge that there may be a clinically relevant benefit of controlling the body temperature at 36°C, instead of allowing fever to develop in patients who have been resuscitated after cardiac arrest,” they wrote.