Resuscitative hypothermia.

Abstract

Resuscitative (postinsult) hypothermia is less well studied than protective-preservative (pre- and intra-arrest) hypothermia. The latter is in wide clinical use, particularly for protecting the brain during cardiac surgery. Resuscitative hypothermia was explored in the 1950s and then lay dormant until the 1980s when it was revived. This change occurred through the discoveries of brain damage mitigating effects after cardiac arrest in dogs, and after forebrain ischemia in rats, of mild (34 degrees C) hypothermia (which is safe), and of benefits derived from moderate hypothermia (30 degrees C) after traumatic brain injury or focal brain ischemia in various species. The idea that protection-preservation or resuscitation by hypothermia is mainly explained by its ability to reduce cerebral oxygen demand has been replaced by an increasingly documented synergism of many beneficial mechanisms. Deleterious chemical cascades during and after these insults are suppressed even by mild hypothermia. Prolonged moderate hypothermia carries some risks, e.g., arrhythmias, infection and coagulopathies. These side effects need further study. In global brain ischemia, protective-preservative mild hypothermia provides lasting mitigation of brain damage. Resuscitative mild hypothermia, however, may be beneficial in terms of long-term outcome or may merely delay the inevitable loss of selectively vulnerable neurons. Even if the latter is true, mild hypothermia may extend the therapeutic window for other interventions. This extension of the therapeutic window requires further documentation. After normothermic cardiac arrest of 11 mins in dogs, mild resuscitative hypothermia from 15 mins to 12 hours after reperfusion plus cerebral blood flow promotion normalized functional recovery with the least histologic damage seen thus far. Optimal duration of, and rewarming methods from, resuscitative hypothermia need clarification. The earliest possible induction of mild hypothermia after cardiac arrest seems desirable. Head-neck surface cooling alone is too slow. Among many clinically feasible rapid cooling methods, carotid cold flush and peritoneal cooling look promising. After traumatic brain injury or focal brain ischemia, which seem to still benefit from even later cooling, surface cooling methods may be adequate. Resuscitative hypothermia after cardiac arrest, traumatic brain injury, or focal brain ischemia should be considered for clinical trials.