The report of the Prophylactic Hypothermia Trial to Lessen Traumatic Brain Injury—Randomized Clinical Trial (POLAR-RCT) by Cooper and colleagues1 in this issue of JAMA describes an international, multicenter, randomized clinical trial of early therapeutic hypothermia after traumatic brain injury (TBI) to increase favorable functional outcomes.
The hypothesis tested in this trial was that hypothermia could reduce intracranial pressure, inflammatory mediator release, free radical generation, and numerous other secondary injurious processes such that functional recovery would be improved.2 The 2 clinical conditions for which hypothermia has been most extensively studied are cardiac arrest and TBI. Cardiac arrest results in temporary global cerebral ischemic injury and TBI involves a heterogeneous condition that includes focal and diffuse components. The potential mechanisms of action may be different for these 2 conditions.