Reducing body temperature after cardiac arrest or after a stroke can reduce the cellular metabolism of tissues in the heart or brain, preserving them from damage caused by hypoxia.
This procedure has very distant origins, since ancient Egypt, but its use has spread more since the early 2000s, following the publication of different clinical trials that demonstrated its benefits.
However, a recent study, published in the New England Journal of Medicine, seems to deal a severe blow to this method, highlighting its poor efficacy in terms of survival, in patients who survived cardiac arrest.
The aim of this new study was to evaluate the beneficial and harmful effects of hypothermia, compared to normothermia, with early treatment of fever, in patients after cardiac arrest. Body temperature management was adopted considering that fever was proposed as a risk factor for an adverse neurological outcome after cardiac arrest.
The study was conducted in an open-label design, with blinded evaluation of the results, and included 1,900 adults with coma who had had out-of-hospital cardiac arrest of presumed cardiac or unknown cause. Patients were randomized to two treatment arms: targeted hypothermia at 33 °C, followed by controlled rewarming, or targeted normothermia with early fever treatment.
The primary endpoint of the study was death from any cause at six months. A fever was considered for a body temperature greater than or equal to 37.8 °C. The main secondary endpoint was a poor functional outcome at 6 months, defined as a score comprised from 4 to 6 on the modified Rankin scale.
Some prespecified adverse events were also evaluated: pneumonia, sepsis, bleeding, arrhythmia resulting in hemodynamic compromise and skin complications related to the temperature management device.
The subjects analyzed had an average age of about 64 years and were mostly males. About half of them had had cardiac arrest at home and in about 80% of cases cardiopulmonary resuscitation maneuvers were applied by bystanders. Most patients presented an arrhythmia potentially treatable with shock, mainly ventricular fibrillation. Just over 10% had asystole. Approximately 40% of subjects had ST segment elevation myocardial infarction.
Among the adverse events considered, arrhythmia resulting in hemodynamic compromise was more common in the hypothermic group than in the normothermic group, but the incidence of other adverse events was not different between the two groups.
The use of therapeutic hypothermia is based on very solid pathophysiological principles and many positive effects have been documented with this method on both the brain and the heart. Based on these data, several international guidelines recommend targeted temperature management to prevent hypoxic-ischemic brain damage in patients with coma after cardiac arrest, even if admitting a low level of evidence.
This new research, conducted on a large number of patients, seems to leave no hope for the effectiveness of this method, both in terms of survival and residual disability.
The authors explain the discrepancy of results with other trials, which had shown positive effects of hypothermia, attributing it to methodological errors of previous studies. On the other hand, they admit that a critical role in obtaining benefits from this method could be the interval between the cardiac event and the moment of onset of hypothermia.
Although this study did not include a true control group, in which no temperature management was performed, there is still clear evidence that, in patients with coma after cardiac arrest, hypothermia did not lead to a lower incidence of death at six months compared to normothermia.
This post is also available in: Chinese (Simplified)