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  • William W. Forgey, MD

Environmental Injuries part 1 of 3 - Hypothermia

Updated: Nov 12, 2020

Excerpt from The Prepper's Medical Handbook. Page reference numbers point to more in-depth treatment and self-reliant care available within the book.


No matter where you go off the grid, while ankle sprains, blisters, and diarrhea are the most common problems that may bother you, environmental conditions pose the most likely threat to life. In fact, most of prepping goes into preparing for environmental injuries. The basic skills involving shelters and fire and energy production are all meant to control environmental challenges. Foremost among these dangers is hypothermia. Death from heat exposure is still the second leading cause of death among high school athletes (discounting the highway). Unless you live right on the Pacific Coast, lightning can do more than scare you. And for those of us forced to suddenly travel vertically, high-altitude illnesses are potentially miserable, even lethal, experiences. This chapter covers injuries that can occur depending on environmental conditions. HYPOTHERMIA The term hypothermia refers to the lowering of the body's core temperature to 95°F (35°C); profound hypothermia is a core temperature lower than 90°F (32°C). Another important point is that the term hypothermia applies to two distinctly different diseases. Chronic hypothermia is the slow onset of hypothermia in the outdoor traveler who is exposed to conditions too cold to be protected by his equipment. Acute hypothermia, or immersion hypothermia, is the rapid onset of hypothermia in a person immersed in cold water. In acute hypothermia—when the onset of cold core temperature takes less than 2 hours—the body cannot produce the complex physiological responses that it is capable of when it has more time. In chronic hypothermia—when body temperature takes 6 hours or longer to arrive at the cold core—the responses are quite dramatic and include profound dehydration, exhaustion, and complex chemical changes in the blood. The ideal treatment is quite different in the hospital setting; in the field our treatment options are reduced to basic techniques of preventing further heat loss and some passive reheating maneuvers. Chronic Hypothermia You do not have to be in a bitterly cold setting to die of hypothermia. In fact, most chronic hypothermia deaths occur in the 30°F to 50°F (0 to 10°C) range. This temperature range places almost all of North America in a high-risk status year-round. To survive hypothermia, be prepared to prevent it, recognize it if it occurs, and know how to treat it. Dampness and wind are the most devastating factors to be considered: Dampness can reduce the insulation of clothing and cause evaporative heat loss, and the increased convection heat loss caused by wind can readily strip away body energy—the so-called windchill effect. Currently, many television weather forecasters discuss a “feels-like temperature” to indicate either a coolness noticeable | at cold temperatures from wind or a warmness felt at hot temperatures with associated humidity. But windchill is an incredibly important concept in understanding the importance even a slight breeze has with regard to stripping body heat away from you and in knowing to immediately consider whatever shelter you can find-even a solitary tree—to minimize this loss if clothing is inadequate. Once, while a small group of us were waiting for a bus in freezing temperatures in a remote area of Leningrad, we simply took turns hiding behind each other as a windbreak. And many times, in a wilderness, I ducked behind that solitary tree! Factors important in preventing hypothermia are a high level of physical conditioning, adequate nutritional and hydration status, avoiding exhaustion, and availability of adequate insulation. There is increased risk of “trauma hypothermia” in the case of injury, especially shock. Even in mild temperatures, a person in shock can become hypothermic. It is very important to insulate persons who are injured from the environment, particularly by providing ground insulation. An initial response to cold is vasoconstriction, or the clamping down of surface blood vessels. This prevents heat from being conducted to the surface by the blood, and effectively increases the thickness of the mantle, or outer layer depth, for increased insulation. Those who become profoundly hypothermic, with a core temperature below 90°F (32.2°C), have concentrated their blood volume into a smaller inner core. The amount of dehydration in these persons can be profound, approaching 5.8 quarts (5.5 liters) in someone below 90°F, equivalent to the entire circulatory volume. This fluid loss comes not only from the vascular space but also from fluid between the cells and within the cells as the body slowly adjusts to the continuing heat loss by shrinking blood circulation into the core and increasing the thickness of the mantle layer. Cold diuresis, an increased urination, is part of this response. At this point, rapid, sudden rewarming can lead to rewarming shock. Hospital methods of rewarming must be coupled with tight metabolic control by adjusting blood factors such as clotting, electrolytes, and blood sugar levels. In chronic hypothermia, rewarming shock and loss of metabolic control are the causes of death, not the so-called afterdrop phenomenon. Afterdrop, or the further lowering of core temperature after rewarming has started, is due to the combination of conduction equilibration of heat and a circulation component. By far the most important aspect is conduction equilibration. This physical property of conduction results in an equilibration of thermal mass as the higher warmth of the core leaches into the colder mantle layer. The amount of afterdrop that occurs is primarily dependent upon the rate of cooling prior to the rewarming process, not the method of rewarming! The goal of treatment for the chronic hypothermic victim is to prevent further loss of heat; this generally means providing shelter and/or more adequate clothing. Persons who are cold may well become hypothermic, and, if they are not exhausted, the best method of warming is to continue exercise. If the victim is exhausted, she will require rest and food. She is dehydrated and requires fluids. If she can stand, a roaring fire can provide adequate, controlled heat. Since chronic hypothermia victims are usually exhausted, however, they will then not be able to exercise themselves to warmth. Exercise is a method of generating heat, as is shivering, but when energy stores are consumed, exhaustion commences and significant hypothermia will begin unless further heat loss is stopped. Deepening hypothermia will lead to a semicomatose state—and worse. This victim needs to be evacuated and hospitalized. Obviously, the real salvation of this situation is a warm shelter, but if you are stuck in the elements, wrap to prevent further heat loss and transport to warmth as soon as possible. Chemical heat packs and the like can be added to the wrap to help offset further heat loss, but this will not add enough heat to rewarm the patient, and thus having these items in your survival kit is practically worthless. If you're heating bottles of water to provide external heat, care must be taken not to burn the victim. If evacuation is not feasible, add heat slowly to avoid rewarming shock. Huddling the victim between two rescuers in an | adequate sleeping bag may be the only alternative. Acute Hypothermia Afterdrop is, however, a real problem for the acute or immersion hypothermic who has had a significant exposure to cold water. As a rule of thumb, a person who has been in water of 50°F (10°C) or less for a period of 20 minutes or longer is suffering from a severe amount of heat loss. That individuals thermal mass has been so reduced that he is in potentially serious condition. He should not be allowed to move around, as this will increase the blood flow to his very cold skin and facilitate a profound circulatory-induced afterdrop-one so great as to be potentially lethal. If this same person is simply wrapped in a litter and not provided with outside heat, there is a real danger his core temperature will cool down to a lethal level because of this profound amount of heat loss. The ideal treatment is rapid rewarming of the acute hypothermic by placing him in hot water (110°F, or 43°C) to allow rapid replacement of heat. The acute hypothermic may have an almost normal core temperature initially, but it is destined to drop dramatically as his body equilibrates his heat store from his core to his very cold mantle. A roaring fire can be a lifesaver. If not available, huddling two rescuers with the victim in a large sleeping bag may be the only answer—the same therapy that might have to be employed in the field treatment of chronic hypothermia under some conditions. The person who has been immersed for less than 20 minutes in cold water can do anything he wants to rewarm. He can run around like crazy, stand by a fire, or just wrap up in warm, dry insulation. The total body thermal mass is still high enough that the temperature equilibration by both the conductive and circulatory components will not reduce the core temperature to a dangerous level. To review, the person who has been in cold water longer than 20 minutes has experienced such a profound heat loss that allowing him to run around or even wrapping him without additional significant heat will cause a tremendous drop in his core temperature-into a lethal range. The person who is fished out of cold water after 2 hours or longer must be considered as approaching chronic hypothermia. He has survived long enough that his physiological protective mechanisms have resulted in dehydration and other changes that are so complex that rapid rewarming can result in shock and death unless he is carefully monitored in a hospital setting. Cold Water Submersion Cold water submersion is always associated with asphyxiation and simultaneous hypothermia. Note that there is a distinct difference between immersion and submersion: Submersion indicates that the victim is entirely underwater; immersion means that the head is above water. Asphyxiation results in brain death, so prompt rescue and immediate implementation of CPR (cardiopulmonary resuscitation) play an important role in the survival of the victim. Total submersion in cold water causes a rapid core cooling, which results in a lower oxygen demand by the brain and other body tissues and increases the chance of survival over that of a victim of warm water submersion. Full recovery after 10 to 40 minutes of submersion can occur. CPR must be continued until the body has been warmed to at least 86°F (30°C). If still unresponsive at that temperature, the victim may be considered dead. It may take several hours of CPR while the patient is being properly rewarmed to make this determination. The rewarming process for immersion victims should not be attempted in the field. Hospital management of victims of cold water submersion is very complex. They are best transferred to centers experienced with this problem, but they will never have a chance if rescuers do not implement CPR immediately. In an off-the-grid situation, the safest approach in rewarming any hypothermia victim is to place them in a warm room, be patient, hydrate if and when they become conscious, and know that there are stories of dead, hypothermic people, waking up after being left for dead in a warm room.


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