Induced hypothermia has been shown to reduce mortality when applied after resuscitation from cardiac arrest.
Current guidelines recommend induced hypothermia for out-of-hospital cardiac arrest (OHCA) shockable rhythms and suggest consideration of induced hypothermia for OHCA nonshockable rhythms and in-hospital patients.
In unconscious adults after out-of-hospital cardiac arrest, mild hypothermia (36°C) appears to be as effective as more extreme hypothermia (33°C) with regard to survival and neurological function.
Induced hypothermia may have benefit for other disease processes such as myocardial infarction and stroke.
The mechanisms by which hypothermia acts are multifaceted and a focus of much current investigation.
The notion of cooling patients for medical benefit is quite old. In 1814, Baron Larrey, a French surgeon in the service of Napoleon’s army, reflected on soldiers who suffered major injuries on the frozen battlefields in Russia by commenting that “cold acts on the living parts … the parts may remain … in a state of asphyxia without losing their life.”1 A belated resurgence of interest in hypothermia has taken place in the past decade, expanding the possible medical indications for its use. Induced hypothermia, the intentional lowering of body temperature, has been explored in a number of acute critical care settings, including myocardial infarction, stroke, head trauma, and after cardiac arrest. While the optimal depth and timing of hypothermia are not yet established for these uses, most experts advocate a temperature goal of 32°C to 34°C because it seems to provide significant benefit while avoiding most of the adverse effects associated with the intervention. Timing of hypothermia, with respect to both time of induction and duration of therapy, is even more uncertain, although general consensus holds that cooling should be initiated as soon as possible after the morbid event and should be maintained for at least 12 to 24 hours. Regarding specific uses, there is particularly good evidence that hypothermia is protective for the resuscitated cardiac arrest patient after return of spontaneous circulation (ROSC).2,3 The use of hypothermia in other clinical scenarios remains promising but less clear at present.
This chapter addresses elements of the history of hypothermia, the laboratory and clinical data that have developed our understanding of its use, some of the various techniques used to cool patients, and the clinical syndromes for which hypothermia appears to offer the greatest advantage.
HISTORY OF INDUCED HYPOTHERMIA
The protective effects of hypothermia induction have been suggested since the time of Hippocrates, who advocated packing bleeding patients in snow.4 Hypothermic protection was also noted by Napoleon’s battlefield surgeon, Baron Larrey, during the French invasion of Russia. He observed improved survival of injured soldiers left in the snow compared with those treated with warm blankets and heated drinks.1 Induced hypothermia has been studied in a wide variety of illnesses, both ischemic and nonischemic in nature (reviewed in refs. 5 through 7). These include ...