There are several militarily relevant aspects of managing the cold casualty in the field, including resuscitation, rewarming, and human tolerance to cold environments. Medical officers should keep in mind that the time available to resuscitate hypothermic casualties is prolonged because of their slowed metabolism. As the familiar saying implies "You are not dead until you are warm and dead." In addition, we should never underestimate the difficulty of carrying out seemingly simple interventions in a combat zone. It is clear that still-unresolved problems of field resuscitation are areas in which the military medical research establishment can play an important role
Resuscitation and Rewarming
Chapter 14, Clinical Aspects of Freezing Cold Injury, contains an extensive discussion concerning various rewarming modalities in the field and in the hospital. In many situations, military personnel may be faced with rewarming a person in the field. For mild hypothermia, having the person drink warm fluids and removing him or her from a cold environment should be more than adequate. After approximately 30 minutes of mild hypothermia, mild exercise is a very effective way to rewarm a victim of hypothermia. However, in certain situations, rewarming involving external methods may be implemented. Exhibits 11-4 and 11-5 list major rewarming techniques and contraindications to cardiopulmonary resuscitation (CPR) that any rescue group needs to consider. In a field operation, the options for rewarming are limited, and many methods of rewarming that have been proposed over the years may not be effective
One point should be emphasized: body-to-body rewarming is not an effective technique. Giesbrecht and colleagues reported that in humans who were made mildly hypothermic by immersion, shivering in a sleeping bag was just as effective as body-to body rewarming. In fact, the hypothermic subject's shivering was blunted by body-to-body rewarming In their conclusions, the authors recommend that subjects who are mildly hypothermic should be removed from their environment and rewarmed. In the field, when logistical considerations prevent evacuation, they recommend any form of external heat, including direct body-to-body contact. Such a recommendation is fraught with a number of problems. Over the years, victims of hypothermia have been found together in a sleeping bag, dead More than likely, these deaths were a consequence of the mistaken assumption that one person can adequately rewarm another who is hypothermic. If the hypothermic individual is shivering, the addition of a warm body will suppress shivering. If the victim is severely hypothermic and is not shivering, the addition of one warm body will not be adequate to rewarm the subject. Also, rewarming may induce rewarming-induced core temperature afterdrop, leading to rewarming collapse (discussed below) Unsubstantiated studies of body-to-body rewarming practices suggest that three normothermic, seminude subjects be placed around the seminude victim of hypothermia, all four in interconnected sleeping bags. Such a solution is neither practical nor recommended, but it does emphasize the fact that one person, no matter how warm, cannot warm a victim of severe hypothermia.
Core Temperature After drop and Rewarming Collapse
The major problem facing the transport of victims of hypothermia is the fact that any form of rewarming may induce major pathological responses of the cardiovascular system, leading to what is called rewarming collapse. This problem the is so controversial and difficult to control in field that some have advocated that (1) any hypothermic victim should simply be removed as quickly as possible to a hospital site and (2) minimal efforts should be taken to rewarm the subject in the field. Core after drop refers to the additional decrease in core temperature that can occur when a hypothermic individual is removed from the cold exposure. The importance of core afterdrop is that if severe enough, it will trigger syncope and even ventricular fibrillation. Core afterdrop and its effects may be the major explanation for the deaths of victims of hypothermia after they have been rescued and rewarmed
Core afterdrop has two major mechanisms of action: conductive and convective. As a person becomes hypothermic, a temperature gradient is established between the cooler periphery and the warmer core. Each layer from the core to the periphery is cooler than its immediately superficial layer. When a person is rewarmed, the temperature gradient is reversed, but the temperature of each layer from the core out to the periphery will continue to fall until the layer just superficial to it is warm. This phenomenon has been seen in both inanimate and animate objects. However, afterdrop has another component. As victims of hypothermia are warmed the process causes their peripheral blood vessels to