Noninvasive Cerebral Cooling in a Swine Model of Cardiac Arrest

Objective: Mild cerebral hypothermia improves neurologic outcome in animals resuscitated from cardiac arrest. This study examined whether one practical external cooling method, i.e., local application of ice to the heads and necks of swine, during resuscitation induces cerebral cooling.
Methods: Local external cerebral cooling was examined in a prospective laboratory investigation using 24 female swine in a model of cardiac arrest. The swine were randomized into hypothermia and normothermia groups. Intracerebral temperature was measured in the parietal cortex. Eight minutes after induction of ventricular fibrillation, chest compressions and mechanical ventilation were initiated. The hypothermia group was treated with 1,500 mL of ice in plastic bags applied to the head and neck, while the normothermia group received no extra interventions. Data were analyzed using repeated-measures ANOVA.
Results: In the normothermia group, there was no significant change in nasopharyngeal (-0.8 ± 0.6°C), intracerebral (-0.6 ± 0.8°C), or esophageal (-0.2 ± 0.6°C) temperatures during 20 minutes of resuscitation. However, in the hypothermia group, application of ice during resuscitation significantly reduced nasopharyngeal (-2.9 ± 1.4°C), intracerebral (-2.1 ± 0.6°C), and esophageal (-1.4 ± 0.8°C) temperatures.
Conclusions: External application of ice packs during resuscitation effectively reduced intracerebral temperatures in swine by an amount that improved neurologic outcomes in previous large animal studies. These data suggest that clinically significant cerebral cooling could be accomplished with a noninvasive, inexpensive, and universally available intervention. Further studies are required to assess the clinical feasibility and therapeutic efficacy of this intervention.