Chapter 8 - HYPOTHERMIA AND COLD INJURIES

Hypothermia, cold exposure, general cooling, and local cooling

Hypothermia is an abnormal and dangerous condition in which core temperature drops below the required temperature for normal metabolism and body functions; which is defined as below 95.0ºF (35.0ºC), ascertained by a low-reading thermometer. A special low temperature thermometer, that measure accurately below 94ºF (34.4ºC) can be placed rectally, esophageally, or in the bladder. Body temperature is usually maintained near 98-100ºF (36.5-37.5ºC) through thermoregulation. If exposed to cold and the internal mechanisms are unable to replenish the heat that is being lost, in spite of further efforts, a drop in core temperature occurs. Hypothermia is the opposite of hyperthermia, which is present in heat exhaustion and heat stroke. An artificially induced hypothermia (86ºF or 30ºC) can be used in the treatment of head injuries and in cardiac surgery. It reduces the oxygen consumption of the tissues and thereby allows greater and more prolonged interference of normal blood circulation.

Hypothermia is divided into four different degrees:

Cold exposure. Hypothermia is usually caused by prolonged exposure to cold and/or damp conditions. Even a slight drop in temperature triggers the regulatory system to turn up the heat through shivering, which generates heat through muscular activity, and cutaneous vasoconstriction, which shunts blood away from the skin and the cold environment to which the skin is exposed. Ventilation diminishes as the respiratory control center becomes depressed. As metabolic heat production decreases, the core temperature falls lower, anoxia increases, and metabolism is further decreased. Characteristic symptoms occur such as shivering and mental confusion. By the time core temperature falls to around 83ºF (28.3ºC), the regulatory mechanisms are entirely overwhelmed. Atrial fibrillation is common, and anoxia death is close by. Ventilation shortly ceases entirely, and lacking oxygen to fuel the metabolic heat generators, the body temperature begins dropping even faster (especially if the victim is wet). Respiration is shallow and slow, the heart rate is faint and slow, and the victim may appear to be dead. People who are very old or very young, people who have cardiovascular problems, and people who are injured, hungry, tired, or under the influence of alcohol are most susceptible to hypothermia.

The lower limit of survival is said to be a core temperature of about 74ºF (23.3ºC). December 2010, a seven-year-old girl in Sweden involved in a drowning incident, recovered from a body temperature plummeted to 55.4ºF (13.0ºC). This case illustrates that victims with accidental hypothermia merit extraordinary resuscitative efforts. When the core temperature falls below 86ºF (30ºC), heart sounds may not be audible even if the heart is still beating; blood pressure may be unobtainable; and pupillary reflexes may be blocked. At 86ºF, the brain can survive without perfusion for about 10 minutes. At 68ºF (20ºC), the brain may be able to manage for 25 to 30 minutes without perfusion (Caroline, 1983).

Hypothermia depresses cardiac function, decreases cerebral blood flow and oxygen requirement, reduces cardiac output, and decreases arterial blood pressure, prolongs acidosis, diminishes the effectiveness of CPR, increases oxygen consumption while decreasing oxygen delivery to the tissues, reduces tissue perfusion, causes defects in coagulation and impairs platelet functions, which leads to increased bleeding times. Hypothermia can cause vital organ dysfunction and fluid shifts and make resuscitation more difficult. Heat is lost through the skin and lungs, and generated through muscle contractions (exercise and shivering).

When the body temperature decreases, changes in the cardiovascular system, leading to the Osborn J wave, the classical ECG finding of hypothermia, and other arrhythmias (ventricular fibrillation and asystole), decreased CNS electrical activity, non-cardiogenic pulmonary edema, and cold diuresis. One complication of hypothermia is that the heart becomes very sensitive and can be easily jolted into an irregular rhythm. Ventricular fibrillation frequently occurs at 82.4ºF (<28ºC) and asystole at 68ºF (<20ºC). Physicians are recommended to not declare a patient dead until his or her body is warmed to a normal body temperature, since extreme hypothermia can suppress heart and brain function.

In temperatures below 59ºF (15ºC), the human body generally begins to experience some functional impairment when unprotected. The hands and fingers lose sensitivity. The body reacts with vasoconstriction; reducing heat loss to the environment but cooling the skin with a resultant chilling of the extremities. Thereafter muscular hypertonus and shivering become mechanisms of maintaining body temperature. Heat is lost more quickly in water than on land. MS Estonia, was a cruise ferry, the ship’s sinking in the Baltic Sea in rough weather on September 28, 1994, claimed 852 lives and was one of the worst maritime disasters of the 20th century. By the time the rescue helicopters arrived, around a third of the people who escaped from the Estonia had died of hypothermia (Soomer, Ranta, & Penttilä, 2001). The United States Coast Guard and the Canadian Coast Guard recommend you to wear your life jacket at all times as it enhances the chance of survival in cold water.

General cooling, is caused by prolonged exposure to low temperatures, especially when there is wind and wet conditions. Any condition that decreases heat production, increases heat loss, or impairs thermoregulation may contribute. It is frequently seen in winter among, the alcoholic, who fall asleep in a doorway or alley and is too sedated by the alcohol (a vasodilator) to notice that the cold before the exposure itself produces further sedation. Other groups, such as divers, mountaineers, and skiers or elderly people living in poorly heated homes, substance abusers or homeless people are also at risk. Hypothermia also is observed in severe cases of anorexia nervosa, and in persons with hypoglycemia, hypothyroidism, sepsis, decreased metabolic rate, and inactivity. The thermoregulatory mechanisms in infants and children are not as well developed as those in adults, and infants and children are prone to hypothermia. The elderly are also prone to heat loss and chilling and become dehydrated sooner than the young. Even in mass casualty situations or disasters, when the injured remains lying down for a long time until rescue (fractures, open wound), hypothermia may occur.

Local cooling, it is possible to get frostbite within minutes during extremely cold conditions. Other cold injuries, caused by exposure to extreme cold, that can either be present alone or in combination with hypothermia include:

• Frostnip is a superficial cooling of tissues without cellular destruction; the initial stages of frostbite are sometimes called frostnip.
• Chilblain (pernio), redness and swelling of the skin caused by excessive exposure to cold, or when a predisposed person is repeatedly exposed to cold. Burning, itching, blistering, and superficial ulcers of the skin similar to those characteristic of a thermal burn may occur.
• Frostbite involves freezing and destruction of tissue. It is a traumatic effect of extreme cold on skin and subcutaneous tissues. A loss of feeling and a white and pale appearance in fingers, toes, nose or ear lobes are symptoms of frostbite.
• Immersion foot (trench foot) is an abnormal condition of moist gangrene of the feet caused by prolonged exposure to dampness or by prolonged immersion in cold water. It is characterized by damage to the muscles, nerves, skin, and blood vessels.

Assessment of patients with hypothermia and cold injuries

Hypothermia, when the outside environment gets too cold or the body's heat production decreases, hypothermia occurs. Hypothermia is defined as having a core body temperature less than 95.0ºF or 35.0ºC. Signs and symptoms of hypothermia:

• Mild hypothermia. Physiological responses to preserve heat may occur, such as shivering, hypertension, tachycardia, tachypnea, and vasoconstriction. Cold diuresis, mental confusion, hypoglycemia, and hepatic dysfunction may also be present.
• Moderate hypothermia, the victim is conscious, but usually apathetic, lethargic. Movements are slow and labored, accompanied by a stumbling pace and mild confusion. Shivering becoming more violent; skin pale and cold to touch. Lips, ears, fingers and toes may become blue. Suspect hypothermia in any elderly or chronically ill victim found in an environment less than 50ºF (10ºC).
• Severe hypothermia, the victim is unconscious or stuporous. The skin is ice cold; heart sounds inaudible; blood pressure unobtainable; and pupils unreactive. Very shallow and slow respirations. The pulse rate and respirations may be difficult to detect but may actually be present.

Paradoxical undressing typical occurs during moderate to severe hypothermia, as the victim becomes confused, disoriented, and combative. They may take of their clothes, because they feel overheated, which in turn, increases the rate of heat loss and make them freeze to death. Some rescuers or bystanders may assume incorrectly that urban victims of hypothermia have been subjected to a sexual assault.

Terminal burrowing, a burrowing-like behavior produced by the brain stem can be present in the final stages of hypothermia. Victims with severe hypothermia are often find in small, enclosed spaces, such as in closets or under beds.

Frostbite occurs when isolated parts of the body; most frequently the ears, nose, hands, feet and digits, are exposed to prolonged or intense cold. The exposed area first becomes red and inflamed, and then progressively turns grey or mottled white. If freezing occurs, the affected area takes on a waxy, white appearance and becomes stiff and hard. In the early stages of frostbite, both superficial and deep injuries show the following signs and symptoms:

• Stinging and burning pain.
• Numbness.
• Waxy-white or mottled-blue discoloration.
• Stiffness with complete loss of sensation.
• Impaired movement.

Frostbite is a serious cold weather-related injury that requires immediate medical attention and rapid rewarming. Re-freezing of thawed frostbitten tissue can increase the severity of the original injury.

Classification of local cold injuries:

• First-degree: hyperemia and edema without skin necrosis.
• Second-degree: large clear vesicle formation (blisters) in addition to hyperemia and edema with partial-thickness skin necrosis.
• Third-degree: full thickness with subcutaneous tissue necrosis, often with hemorrhagic vesicles.
• Fourth-degree: full thickness and subcutaneous tissue necrosis, also involving muscle and bone with gangrene.

Wind chill is a calculation of how cold it feels outside when the effects of temperature and wind speed is combined. Because wind chill factors are based on exposure of dry skin to cool air currents, air blowing at the same speed over a wet skin surface would cause additional loss of body heat and a greater wind chill. Frostbite is a severe reaction to cold exposure, and hypothermia can also occur during winter storms. How fast the signs of frostbite develop depends on the air temperature, wind chill factor, and how well the affected body part is protected. Change to dry clothes as soon as possible to avoid heat loss.

Risk factors for frostbite include using beta-blockers and having conditions such as diabetes and peripheral neuropathy. The elderly, those with disabilities, individuals with paralysis and those who have difficulty sensing and maintaining heat in their extremities need to be extra careful and protect themselves; such as being out in the warmest part of the day if possible, and by wearing several layers of clothes.

Prevention of cold weather-related injuries is best accomplished through proper planning and preparation for cold weather. Appropriate clothing helps to prevent hypothermia. Synthetic and wool fabrics are superior to cotton as they provide better insulation when wet and dry. Preparing vehicles for the winter season can save many lives.

Management of patients with hypothermia and cold injuries

Treatment include warming the patient; and ranges from passive external rewarming, to active external rewarming, to active internal (core) rewarming. The treatment of moderate hypothermia is aimed at preventing further heat loss and rewarming the patient as rapidly as possible. The severely hypothermic patient is extremely vulnerable to arrhythmia, and requires very gently handling to prevent any sudden movements. In severe cases resuscitation begins with simultaneous removal from the cold environment, and concurrent management of the airway, breathing, and circulation. If close to the hospital, transport patients with severe frostbite without delay.

• Adhere to the ABCDEs (Airway, Breathing, Circulation, Disability, Exposure/environment control) of resuscitation. Ensure airway, breathing, and circulation. Administer oxygen as ordered. Assist ventilations as indicated (if respiratory rate is less than 5/minute, but do not hyperventilate), and anticipate shock. The blood pressure may be unobtainable, respirations are likely to be very slow, and the pupils are often entirely unreactive to light. Extreme hypothermia can suppress heart and brain function, and the patient appears to be dead. Full resuscitation should include warming the body appropriately according to the degree of hypothermia.
• Move the patient to a protected area, out of the wind and, if possible, out of the cold. Replace wet clothing or cut away wet clothing and replace with dry clothing.
• Identify the type and extent of cold injury. Measure the patient's core temperature.
• Secure intravenous access. In these cases, cardiac arrhythmias are common, and intravenous access facilitates the administration of warmed intravenous fluids and the rapid administration of resuscitative medications if paradoxical rewarming collapse (or rewarming shock) occurs. It is a sudden drop in blood pressure in combination with a low cardiac output, which may occur during active treatment of a severely hypothermic patient.
• Start electrocardiographic monitoring. Monitor the patient’s cardiac rhythm, and start external compressions if you see asystole or ventricular fibrillation on the scope. A pulse may not be palpable (and heart sound may not be audible). Respirations may also be difficult to detect. The same low temperatures that put the heart in fibrillation confer considerable protection on the brain against the effects of hypoxia. The outcome of CPR cannot be properly accessed until after the patient has been fully rewarmed, but do not give up, because full recovery is possible. If defibrillation attempt fail to terminate ventricular fibrillation, they should stop until a body temperature higher than 86ºF (30ºC) is obtained. “Nobody is dead until warm and dead”.
• Insert an indwelling urinary catheter, as ordered. Cold diuresis is often present.
• Look for contributing conditions including: diabetes, sepsis, signs of substance abuse, alcohol, and head injury. Monitor blood test results.
• Guard against hypothermia by covering the child and protecting against heat loss when possible. Keep the elderly patient warm by covering him or her with blankets, because they lose heat easily, but do not obscure observation of injuries.
• Forced-air warming is a method to prevent unintended hypothermia and its complications. Warming fluids and humidifying oxygen are methods of reducing heat loss, head wraps, blankets, and plastic of foil coverings also may help maintain warmth.
• Mild hypothermia – Passive rewarming involves using body heat, properly insulated dry clothing, or ambient room temperature to aid the person's body in rewarming itself. This includes wrapping in blankets or moving to a warmer environment.
• Moderate hypothermia – Active external rewarming is aimed at preventing further heat loss and rewarming the patient by applying warming devices externally. Move the patient to a protected area, out of the wind and, if possible, out of the cold. Replace wet clothing with dry clothing. Cover with insulating materials and blankets (leaving only the face free). When performed, active rewarming seeks to warm the injured tissue as quickly as possible without burning them. Active rewarming is usually achieved by immersing the injured tissue in a water-bath that is held between 99-104°F (37-40°C). Warming of peripheral tissues can increase blood flow from these areas back to the bodies' core. This may produce a decrease in the bodies' core temperature and increase the risk of cardiac arrhythmias. Cardiac monitoring during rewarming and defibrillation preparedness (experienced staff, if possible).
• Severe hypothermia – Active internal rewarming is the use of intravenous warmed fluids, irrigation of body cavities with warm fluids. The severely hypothermic patient is extremely vulnerable to ventricular fibrillation, and even the slightest jolt may trigger this arrhythmia; these patients must be handled very gently (like fragile glass). Cut away wet clothing and replace with dry clothing. Apply warmed force air (Bair Hugger) if available, or core (inhalation, warmed infusion and peritoneal lavage, extracorporeal blood rewarming). Cardiac monitoring during rewarming and defibrillation preparedness (experienced staff, if possible).
• Early management of cold-injured patients includes: Treatment should be immediate but rewarming should not be started if there is the risk of refreezing. Replace constricting, damp clothing by warm blankets. Give hot fluids to drink if possible (not alcohol), but only to fully awake patients. Unless the skin is insensitive, place the injured part in circulating water at a 102-104°F (39-40°C) until the pink color and perfusion return (usually within 20 to 30 minutes). Avoid dry heat and do not rub or massage the area. Rewarming can be very painful; adequate analgesia. Cardiac monitoring during the rewarming process to watch for any irregularities.
• Local cold injuries should have tetanus prophylaxis. A tetanus booster shot is required if the patient has not been immunized within the last 5 years.
• The area affected by frostnip usually does not become permanently damaged as only the skin's top layers are affected. The affected part may be slowly warmed by breathing onto the injured site. A hand with frostnip can also be warmed under the armpit. Numbness gives way to a warm flush feeling that can be painful. With time, frostnip will heal by itself. Long-term sensitivity to both heat and cold can sometimes happen after suffering from frostnip.
• Chilblain treatment includes protection against cold and injury, gently warming, and avoidance of tobacco.
• Any person with frostbite injury should be immediately transported to a medical facility. Do not make affected areas (skin) touch any cold or hot objects. Trying to warm frostbitten skin at the scene can cause more harm than good. Re-freezing of thawed frostbitten tissue can increase the severity of the original injury. Remove the victim from the cold, and gently remove gloves, shoes, and socks from the affected area. Loosen tight clothing, avoid trauma to the skin. Cover a frostbitten ear and nose with a warm hand; and place a frostbitten hand in the opposite armpit. Gentle warming is appropriate first-aid treatment; rubbing the affected part is avoided. Later therapy is similar to treatment of thermal burn. Do not rupture blisters, apply ointments or tight bandages. Excessive movement of frostbitten tissue can cause ice crystals that have formed in the tissue to do further damage. Do not handle a frostbitten extremity roughly. Avoid dry heat and do not rub or massage the area. Topical or oral antibiotics are often necessary for bacterial infection of the frostbitten tissue. Deep frostbite injury will eventually lead to some shedding of dead tissue over the following weeks to months. Nerve damage in the area can result in a loss of feeling. Estimation of depth and extent of tissue damage are not usually accurate until demarcation is evident. Debridement and/or amputation of necrotic tissue are usually delayed, with exceptions only being made for signs of infections or gas gangrene. Although the surgical management of frostbite involves delayed debridement 1 to 3 months after demarcation, recent improvements in radiological assessment (bone scan) of tissue viability have led to the possibility of earlier surgical intervention.
• Offer explanations and reassurances to the patient as you work. Inform about preventive steps to avoid hypothermia, cold exposure, general cooling, and local cooling.