Induction of Mild Hypothermia in Resuscitated Cardiac Arrest Patients

Extensive research has been conducted in the use of mild hypothermia as a neuroprotectant in acute brain injury in animal models with studies having been initiated as far back as the 1950's. However, little work had been done in the area of therapeutic hypothermia and cardiac arrest.

In the early 80's, the Pittsburgh group resurrected the work with the induction of hypothermia in animals. The discovery of mild resuscitative hypothermia provided evidence that the main mechanism by which hypothermia can help resuscitate the brain after normothermic cardiac arrest is a synergistic effect of the suppression of deleterious chemical cascades, energy loss depolarization, calcium influx, excitotoxicity, free radical reactions, membrane failure, DNA fragmentation, and damage to the mitochondria).

Recently, the study "Mild hypothermia to improve the neurologic outcome after cardiac arrest" from the Hypothermia After Cardiac Arrest Study Group (New Engl J Med 2002;346:549-556) reported the results of a multicenter randomized controlled clinical trial that evaluated the effect of mild systemic hypothermia on mortality and functional outcome after resuscitation from out-of-hospital cardiac arrest due to ventricular fibrillation or tachycardia. Two hundred and seventy three patients were randomly assigned to standard normothermic or hypothermic management. Cooling to a target core body temperature of 32ºC to 34ºC was accomplished with the use of a specialized bed which delivers cold air over the entire body. Temperature was maintained in the target range for 24 hours after the start of cooling, followed by passive rewarming over 8 hours. Outcome was assessed at 6 months with a five point scale similar to the Glasgow Outcome Scale, dichotomized to classify independent patients with minimal or moderate disability to those who were dependent and severely disabled, vegetative, or dead. The results demonstrated a favorable neurological outcome in 55% of the 136 patients treated with hypothermia, compared to 39% of the 137 patients treated with normothermic management (risk ratio 1.40, 95% confidence interval 1.08 to 1.81, P=.009). . Mortality was also reduced with hypothermic management, from 41% in the hypothermia group to 55% in the normothermia group (risk ratio 0.74, 95% confidence interval 0.58 to 0.85, P=.02). In 19 patients (14%), the target temperature could not be reached. Complications did not differ significantly between the two groups, although there were trends toward increased rates of sepsis and bleeding with hypothermia.

Based upon the body of published evidence to date, the Advanced Life Support (ALS) Task Force of the International Liaison Committee on Resuscitation (ILCOR) made the following recommendations in October 2002 (Resuscitation 57 (2003) 231-235):

• Unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32-34°C for 12 -24 hours when the initial rhythm is ventricular fibrillation (VF).
• Such cooling may also be beneficial for other rhythms or in-hospital cardiac arrest

The study is a prospective, randomized, multi-center, pilot study of the Arctic Sun System used as adjunctive therapy in patients resuscitated post cardiac arrest.

Patients who meet the inclusion criteria and for whom informed consent has been provided by an authorized representative/family member will be randomly assigned to either the control group (traditional cooling blankets and ice) or the experimental group (Arctic Sun Temperature Management System).

Patients will be cooled to a target range of 33.5°C to 33.9°C. The patient cooling will continue for 24 hours (from the initiation of cooling) and then gradually rewarmed to 36.0°C over approximately 6 to 12 hours.