What is the use of hypothermia for neuroprotection after out-of-hospital cardiac arrest?

Abstract

Out-of-hospital cardiac arrest (OHCA) refers to the loss of cardiac mechanical activity with hemodynamic collapse in the out-of-hospital setting. If not treated rapidly, OHCA invariably results in death. Survival to hospital discharge after OHCA is low in many communities, ranging between 10.7% (95% confidence interval, 9.9%–11.5%) for adults treated for all rhythms and 31.7% (95% confidence interval, 28.2%–35.1%) for those resuscitated after bystander-witnessed ventricular fibrillation (VF).1 The most common cause of death among patients hospitalized after OHCA is neurological injury.2,3 In spite of these unmet challenges, the in-hospital mortality rate of treated patients has declined 11.8% in recent years, from 69.6% in 2001 to 57.8% in 2009.4 This improvement in outcomes is thought to be related in part to the advent of therapeutic hypothermia, as well as implementation of intensive care protocols for those successfully resuscitated but still comatose after OHCA.4 Reperfusion injury occurs in the brain5 and heart6 during and after restoration of blood flow. It includes release of proinflammatory then anti-inflammatory cytokines, which contribute to poor capillary perfusion, tissue ischemia, and microcirculatory dysfunction. Cardiac function decreases then improves during the initial 2 days. Vascular and intestinal permeability increase during the next 3 days. Patients may experience sepsis-like hemodynamic states,7 neurological injury, multiple organ dysfunction, and death. The extent of reperfusion injury is associated with the duration of ischemia, and the adequacy of resuscitation. In turn, long-term prognosis is correlated with the extent of reperfusion injury. Induction of hypothermia during ischemia prolongs the tolerance of organs to ischemia. Hypothermia after reperfusion reduces production of deleterious glutamate, oxygen-free radicals and inflammatory molecules, cerebral oxygen demand, intracranial pressure, and the final extent of neurological injury.8 Thus, induced hypothermia (IH), sometimes called targeted temperature management, which consists of cooling the body to …