Recent Advances in Hypothermia Research a

Over the past fifty years interest in human accidental hypothermia has increased. As the basic physiology of cooling and etiology of hypothermia have been covered in depth in several review these topics will be briefly summarized with emphasis given to cardiorespiratory responses which affect metabolic, acid-base and hemodynamic status during recovery. The primary effect of body cooling is a decrease in tissue metabolism and inhibition of neural control and transmission. However, in the intact conscious condition, the secondary responses to skin cooling predominate. Therefore, sudden cooling initiates shivering thermogenesis, and increases metabolism (VO2), ventilation WE), heart rate (HR), cardiac output (CO), and mean arterial pressure (MAP). The primary effects of cooling can be seen during anesthesia or at lower core temperatures ( i .e . , <30"C) when shivering ceases and, V,,, HR, MAP, and CO decrease with core temperature while hematocrit and total peripheral resistance increase. There are several classification systems for hypothermia based on core temperature. We use a simple classification system which is based on general functional characteristics: mild hypothermia [core temperature (Tco): 35-30"C, conscious, shivering and locomotion]; moderate hypothermia (Tco: 3O-2S0C, altered consciousness, not shivering, cardiac dysrhythmias); and severe hypothermia (Tco <25"C, unconscious, ventricular fibrillation, asystole, ultimately death). Core temperature measurements are usually not available in the field, and choice of treatment is based on the functional characteristics listed above. The following discussion centers on three topics that are related to survival from accidental