GOAL: Preserving Brain Function after Cardiac Arrest

The exact mechanism by which hypothermia protects the brain remains unknown: possibilities include inhibition of apoptosis.

AHA Guidelines state : "...In summary, providers should not actively rewarm hemodynamically stable patients who spontaneously develop a mild degree of hypothermia (>33 C or 91.5 F) after resuscitation from cardiac arrest. Mild hypothermia may be beneficial to neurologic outcome and is likely to be well tolerated without significant risk of complications. In a select subset of patients who were initially comatose but hemodynamically stable after a witnessed VF arrest of presumed cardiac etiology, active induction of hypothermia was beneficial. Thus, unconscious adult patients with ROSC after out-of-hospital cardiac arrest should be cooled to 32C to 34C (89.6F to 93.2F) for 12 to 24 hours when the initial rhythm was VF (Class IIa). Similar therapy may be beneficial for patients with non-VF arrest out of hospital or for in-hospital arrest (Class IIb).

AHA Guidelines state : "...In summary, providers should not actively rewarm hemodynamically stable patients who spontaneously develop a mild degree of hypothermia (>33 C [91.5 F]) after resuscitation from cardiac arrest. Mild hypothermia may be beneficial to neurologic outcome and is likely to be well tolerated without significant risk of complications. In a select subset of patients who were initially comatose but hemodynamically stable after a witnessed VF arrest of presumed cardiac etiology, active induction of hypothermia was beneficial. Thus, unconscious adult patients with ROSC after out-of-hospital cardiac arrest should be cooled to 32 C to 34 C (89.6 F to 93.2°F) for 12 to 24 hours when the initial rhythm was VF (Class IIa). Similar therapy may be beneficial for patients with non-VF arrest out of hospital or for in-hospital arrest (Class IIb)"

Therapeutic Hypothermia is relatively easy to perform in most ICU settings (see protocol links, above)

As stated in AHA Guidelines, 2005 : Both permissive hypothermia (allowing a mild degree of hypothermia >33 C [91.5 F] that often develops spontaneously after arrest) and active induction of hypothermia may play a role in postresuscitation care. In 2 randomized clinical trials, induced hypothermia (cooling within minutes to hours after ROSC) resulted in improved outcome in adults who remained comatose after initial resuscitation from out-of-hospital ventricular fibrillation (VF) cardiac arrest. Patients in the study were cooled to 33 C (91.5 F) or to the range of 32C to 34C (89.6 F to 93.2 F) for 12 to 24 hours. The Hypothermia After Cardiac Arrest (HACA) study included a small subset of patients with in-hospital cardiac arrest. A third study documented improvement in metabolic end points (lactate and O2 extraction) when comatose adult patients were cooled after ROSC from out-of-hospital cardiac arrest in which the initial rhythm was pulseless electrical activity (PEA)/asystole. In the HACA and Bernard studies, only about 8% of patients with cardiac arrest were selected for induced hypothermia (ie, patients were hemodynamically stable but comatose after a witnessed arrest of presumed cardiac etiology). This highlights the importance of identifying the subset of patients who may most benefit. Although the number of patients who may benefit from hypothermia induction is limited at present, it is possible that with more rapid and controlled cooling and better insights into optimal target temperature, timing, duration, and mechanism of action, such cooling may prove more widely beneficial in the future.11 A recent multicenter study in asphyxiated neonates showed that hypothermia can be beneficial in another select population. Complications associated with cooling can include coagulopathy and arrhythmias, particularly with an unintentional drop below target temperature. Although not significantly higher, cases of pneumonia and sepsis increased in the hypothermia-induction group. Cooling may also increase hyperglycemia. Most clinical studies of cooling have used external cooling techniques (eg, cooling blankets and frequent applications of ice bags) that may require a number of hours to attain target temperature. More recent studies suggest that internal cooling techniques (eg, cold saline, endovascular cooling catheter) can also be used to induce hypothermia. Providers should continuously monitor the patient's temperature during cooling.