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Exact Cooling Temperature Has No Bearing on Overall Prognosis After Cardiac Arrest

Author profile picture By L.A. McKeown

Therapeutic hypothermia for neuroprotection in comatose out-of-hospital cardiac arrest patients offers similarly good cognitive outcomes and quality-of-life (QoL) outcomes regardless of the degree to which body temperature is lowered. Findings from a substudy of the TTM trial were published online April 6, 2015, ahead of print in JAMA Neurology.

The multicenter TTM (Targeted Temperature Management) study randomized 950 unconscious patients after out-of-hospital cardiac arrest to cooling at either 33°C (n = 473) or 36°C (n = 466). In the main results, no differences were seen in mortality or neurological function between the 2 temperature groups after 180 days. 

For the exploratory analysis, researchers led by Niklas Nielsen, MD, PhD, of Helsingborg Hospital (Helsingborg, Sweden), evaluated cognitive function and health-related QoL using:

  • The Mini-Mental State Examination (MMSE)
  • The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE)
  • Two Simple Questions questionnaire
  • Medical Outcomes Study 36-Item Short Form Health Survey, version 2

In a modified intention-to-treat population of 939 patients (including nonsurvivors), the median MMSE and IQCODE scores were similar between the treatment groups (P = .77 and P = .57, respectively).

Over a median follow-up of 6.1 months after cardiac arrest, slightly more than half of patients in both treatment groups remained alive, with 229 in the 33ºC arm and 226 in the 36ºC arm undergoing QoL testing. Prognostic baseline variables, occupational status, and place of stay were similar between patients cooled to 33ºC vs 36ºC. Although the percentage of all patients holding full- or part-time jobs dropped from 50.8% to 31.6%, there was no difference between the groups.

Among survivors, all test scores were similar between temperature groups and within reference or minor deficit range (table 1).

According to the study authors, the findings regarding daily activities and mental recovery were “supported by the report of a relative or close acquaintance, observing a minor decline by IQCODE in half of the survivors and a moderate or severe decline in a quarter.”

The only noteworthy difference between the 2 temperature groups was that more patients in the 33°C group had less than 12 years of education, Dr. Nielsen and colleagues write.

“This random bias may have affected the IQCODE results because informants of disproportionately highly educated patients might have recognized decline more easily,” they add.

Furthermore, the sharp decline in the number of patients working full- or part-time jobs at 6 months suggests that “subtle cognitive dysfunction may be missed” by standard follow-up measures such as the Cerebral Performance Category and modified Rankin scale,” Dr. Nielsen and colleagues observe.

Data Underline High Likelihood of Good Outcome

In an editorial accompanying the study, Venkatesh Aiyagari, MBBS, DM, of the University of Texas Southwestern Medical Center (Dallas, TX), and Michael N. Diringer, MD, of Barnes-Jewish Hospital (St. Louis, MO), say the take-home message of the study “is that although cognitive changes are common, the overall long-term outcome of patients with a [cardiac arrest] who survive to hospital discharge is quite good. Most of these patients are discharged home and report no problems with self-care, and a significant number are gainfully employed.”

Taken together with other studies, the data “reinforce the view that patients who survive a [cardiac arrest] and are unconscious should be managed with intensive support measures, including [targeted temperature management], and premature prognostication should be avoided,” they say. It remains to be seen, they add, whether certain subgroups may benefit from lower temperature targets.

 

Sources:
1. Cronberg T, Lilja G, Horn J, et al. Neurologic function and health-related quality of life in patients following targeted temperature management at 33°C vs 36°C after out-of-hospital cardiac arrest: a randomized clinical trial. JAMA Neurol. 2015;Epub ahead of print.
2. Aiyagari V, Diringer MN. Cognition and quality-of-life outcomes in the Targeted Temperature Management trial for cardiac arrest [editorial]. JAMA Neurol. 2015;Epub ahead of print.

Disclosures:

  • Dr. Nielsen reports receiving lecture fees from Bard Medical.
  • Drs. Aiyagari and Diringer report no relevant conflicts of interest.

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