ABSTRACT & COMMENTARY
Source: Tadler SC, et al. Noninvasive cerebral cooling in a swine model of cardiac arrest. Acad Emerg Med 1998;5:25-30.
This study looked at the efficacy of a simple method to achieve cerebral cooling in the setting of an animal model cardiac arrest. The study design was prospective and randomized. Half of the swine who had an induced cardiac arrest had their heads surrounded by ice during standard resuscitative efforts. The ice and water slurry was in three separate 500cc bags. Bags were placed on either side of the head, and one was placed over the neck. The other half of the animals did not have external cerebral cooling during resuscitation. All animals had three separate temperatures measured: intracerebral, nasopharyngeal, and esophageal. After 20 minutes of resuscitation, the mean temperatures of the experimental group were 2.6°C lower at the nasopharyngeal site, 2°C lower at the intracerebral site, and 2.2°C lower at the esophageal site, compared to the normothermic animals.

Tadler and associates conclude that the magnitude of the temperature decrease with this simple external cerebral cooling method is consistent with the degree of hypothermia that has previously been shown in animal models to be beneficial for neurologic recovery following cerebral ischemia induced by cardiac arrest. Previous studies show that cerebral hypothermia must be induced during ischemia (during resuscitation, not after restoration of blood flow) to have significant beneficial effects on long-term neurologic recovery. Tadler et al point out the simplicity of their technique and how it allows for widespread use during resuscitation if induced cerebral cooling is shown to be beneficial for human victims of cardiac arrest.

COMMENT BY GLENN C. FREAS, MD, JD

When I was a resident in the early 1980s, I recall hearing a well-known resuscitation researcher at a conference say, "If I have an arrest on the street, I want my head placed in a box of ice-do not do CPR, and transport me to a trauma center where they can open my chest and do internal cardiac massage." At the time, his ideas seemed pretty radical, and I thought he was being somewhat facetious. However, the idea of cooling the brain during cardiac arrest has been intuitively appealing for a long time. Case reports of intact neurologic survival of cold water drowning victims, after prolonged submersion, frequently invoke cerebral cooling as one factor responsible for the good outcome. Hypothermia is standard practice in some types of neurosurgery and cardiac surgery.

Animal resuscitation research convincingly shows the beneficial effects of cerebral cooling during cardiac arrest. This study looks at one aspect of this research-techniques for cooling. Keep in mind that Tadler et al did not look at the functional neurologic recovery of their animals. They simply wanted to know if the technique they used for cerebral cooling would achieve temperatures that have previously been shown to be beneficial for neurologic recovery in the setting of cerebral ischemia induced by cardiac arrest. Previous studies of induced cerebral hypothermia used techniques like cardiopulmonary bypass and peritoneal lavage. The technique described here is easy, can be applied in the prehospital setting, and appears to provide the cerebral temperature decrease that has been shown to be beneficial in several animal studies.

The article provides a concise review of some of the proposed biochemical processes that mediate brain injury during ischemia and reperfusion. Tadler et al point out that hypothermia can positively influence several of those mechanisms-unlike proposed pharmacologic interventions, which target a single aspect of ischemia and reperfusion injury. It is clear that much work needs to be done before any of these techniques can be widely studied in humans. If cerebral hypothermia is shown to be beneficial in humans, Tadler et al have potentially made an important contribution toward simplifying the way we can cool cardiac arrest victims' brains.