Cold Injury



Cold Injury



Norman M. Rich and David R. Welling


Cold weather has been known to be a threat to humans since the beginning of recorded history. Cold injury as a threat has intensified during periods of armed conflict. Its devastating results were detailed during the American Revolution and in Napoleon’s campaign in Russia, and similar devastating experiences occurred in World War I, World War II, and the Korean conflict. Frostbite, immersion foot, and trench foot continue to challenge those subjected to cold weather, with or without wet conditions, emphasizing that prevention and successful treatment are not universal.


Preventing cold injury is of paramount importance. Yet, during times of armed conflict, prevention may be increasingly difficult. Cold injury during certain sporting activities such as mountain climbing and skiing also continues to be a significant challenge, particularly for the least-experienced participants. Cold injury usually occurs during combat situations when combatants are exposed to cold weather for prolonged periods without adequate clothing; similar injuries can occur among elderly civilians and those who are intoxicated.



Hypothermia


Hypothermia is a diagnosis made by identifying a temperature by thermometer or thermistor probe below 35°C or 95°F. Elderly persons, who have more difficulty in perceiving temperature changes, are particularly susceptible to hypothermia. Elderly persons with less total body water than those who are younger also have a reduced shivering response and a reduced ability to store heat. The most common symptom of hypothermia is an altered state of consciousness, and this may be evidenced by agitation, confusion, mood changes, poor judgment, and even coma. The patient can appear cyanotic or gray, and the skin is cool to touch. With severe hypothermia, shivering may be absent. Often, blood pressure and pulse rate are decreased.


Increased urinary output with hypothermia can result in volume depletion and dehydration. Normal reabsorption of water and glucose are prevented, and there is a decreased secretion of antidiuretic hormone. Diminished insulin production associated with decreased peripheral glucose utilization can result in hyperglycemia. Acidosis is usually present, and it can be a combination of metabolic and respiratory acidosis. Hemoconcentration and increased blood viscosity occur. There is a partial impairment of the delivery of oxygen to tissues.


If the core body temperature falls below 33°C, severe hypothermia exists. With falling temperature, sinus bradycardia can develop that does not respond to therapy, including atropine therapy. On the electrocardiogram, a slowing of conduction may be seen, as well as T-wave inversion and a characteristic J wave, which is a positive deflection in the left ventricular leads at the junction on the QRS and ST segments.



Frostbite


Following hypothermia, a second major type of cold injury is frostbite, which may be classified into four types depending on the clinical appearance after thawing:



It may be difficult to determine the exact depth of tissue destruction for several days; therefore, a more practical classification may be limited to superficial injury and deep injury.


Frostbite involves freezing of the tissue. Exposed areas most often involved are the ears, feet, hands, and nose, where skin and subcutaneous tissues are frozen in prolonged exposure to cold weather.


In superficial frostbite the skin is blanched initially, and it can have a waxy appearance. Sensation may be diminished or absent. With thawing, the involved part becomes red and warm, and capillary filling is rapid. Within hours, edema appears and large vesicles filled with clear fluid can extend to the tips of digits. Sensation and motor function return. Throbbing pains and paresthesias are common. A black eschar can ultimately result from the vesicles, and the eschar can separate spontaneously, revealing skin that is fragile and hypersensitive underneath. With the healing process, the skin gradually returns to normal.


If the frostbite is deep, the tissues are hard and the deep tissue is not resilient. Prediction of the extent of tissue damage might not be possible for several weeks after the injury. With deeper injuries, capillary circulation is not restored adequately following thawing. The majority of blood flow to the injured part is diverted through arteriovenous shunts. The area affected remains cool to touch and deep red. Distal motor function and sensation might remain intact. If vesicles form, they can take days to weeks to appear, being small and dark or hemorrhagic in appearance.


The pathophysiology of frostbite is a combination of cellular dehydration, extracellular ice crystal formation, and microvascular occlusion. The enlarging extracellular ice crystals draw intracellular water across the cell membrane, resulting in cellular dehydration. There is a resultant increase in intracellular electrolytes and proteins. Cellular microstructures can be disrupted if the concentration of electrolytes is excessive, leading to denaturation of intracellular proteins. There is a protective decrease in metabolic activity when body temperature falls. However, as the cooling process continues, blood flow in small vessels becomes sluggish and finally ceases, with freezing and microvascular occlusion. Even with thawing when blood flow resumes, small vessels become occluded almost immediately by platelet aggregates. Progressive occlusion of capillary and precapillary arterioles can follow, depending on the magnitude of the injury and the type of treatment.

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Aug 25, 2016 | Posted by in CARDIOLOGY | Comments Off on Cold Injury

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