Freezing to DeathFreezing to Death

Frostbite and Frostbite and HypothermiaHypothermia

Cold injuries result from our inability to Cold injuries result from our inability to properly protect ourselves from the properly protect ourselves from the environment. environment.

Factors such as temperature, length of Factors such as temperature, length of exposure, windchill, humidity and exposure, windchill, humidity and wetness play important roles in these wetness play important roles in these processes. processes.

The majority of cold injuries The majority of cold injuries encountered today affect the homeless encountered today affect the homeless and wilderness and sports enthusiasts.and wilderness and sports enthusiasts.

FrostbiteFrostbite

PathophysiologyPathophysiology

Frostbite represents a localized ischemic injury, Frostbite represents a localized ischemic injury, and skin circulation is the critical factorand skin circulation is the critical factor

To preserve the body's core temperature, the To preserve the body's core temperature, the skin's blood flow can vary from 20 ml/min when skin's blood flow can vary from 20 ml/min when the skin temperature is 15° C (59°F) up to 8,000 the skin temperature is 15° C (59°F) up to 8,000 ml/min when the skin temperature is 41°C ml/min when the skin temperature is 41°C (106°F). Blood flow through the apical structures (106°F). Blood flow through the apical structures (i.e. hands, feet, nose and ears) varies the most (i.e. hands, feet, nose and ears) varies the most markedly.markedly.

Our core temperature is defended by Our core temperature is defended by vasoconstriction and shunting of blood away vasoconstriction and shunting of blood away from these structures; thus your body will from these structures; thus your body will sacrifice fingers and toes to maintain its core sacrifice fingers and toes to maintain its core temperature. This has been called the "life-or-temperature. This has been called the "life-or-limb" responselimb" response

Vascular tone is controlled by direct local Vascular tone is controlled by direct local temperature and indirect reflex temperature temperature and indirect reflex temperature effects. An illustration of the latter would be effects. An illustration of the latter would be that a cold head will cause vasoconstriction of that a cold head will cause vasoconstriction of the hands!the hands!

Maximal peripheral vasoconstriction and minimal Maximal peripheral vasoconstriction and minimal blood flow occur when the extremities are cooled to blood flow occur when the extremities are cooled to 15°C (59°F). 15°C (59°F).

At 10°C (50°F), vasoconstriction is interrupted by At 10°C (50°F), vasoconstriction is interrupted by periods of vasodilatation, termed cold-induced periods of vasodilatation, termed cold-induced vasodilatation (CIVD) or the "hunting response." This vasodilatation (CIVD) or the "hunting response." This protects the area from cold injury at the expense of protects the area from cold injury at the expense of increasing heat loss. It occurs in 5-10-minute cycles, increasing heat loss. It occurs in 5-10-minute cycles, and individual variation may explain susceptibility to and individual variation may explain susceptibility to frostbite. frostbite.

Prolonged and repeated cold exposures increase the Prolonged and repeated cold exposures increase the degree of CIVDdegree of CIVD

Eskimos, Lapps and Nordic fishermen Eskimos, Lapps and Nordic fishermen have a strong CIVD with rapid cycling, have a strong CIVD with rapid cycling, which helps them maintain hand function which helps them maintain hand function in the cold. This response is impaired by in the cold. This response is impaired by altitude, hypoxia, dehydration and alcohol.altitude, hypoxia, dehydration and alcohol.

Humans are basically adapted to warm climates. Humans are basically adapted to warm climates. Since humans do not adapt well to the cold, Since humans do not adapt well to the cold, behavioral responses such as putting on behavioral responses such as putting on additional clothing and seeking shelter are key additional clothing and seeking shelter are key to preventing frostbite.to preventing frostbite.

Factors such as mental illness and drug and Factors such as mental illness and drug and alcohol use interfere with these behavioral alcohol use interfere with these behavioral responses.responses.

Hypovolemia, hypothermia and the presence Hypovolemia, hypothermia and the presence of other injuries all add to the severity of of other injuries all add to the severity of frostbite. Diabetes, atherosclerosis, vasculitis, frostbite. Diabetes, atherosclerosis, vasculitis, Raynaud's phenomenon, hypotension and Raynaud's phenomenon, hypotension and the use of vasoconstrictors or vasodilators the use of vasoconstrictors or vasodilators increase the risk and seriousness of frostbite.increase the risk and seriousness of frostbite.

Tight clothing increases the risk of cold injury Tight clothing increases the risk of cold injury by impairing circulation. Sweating accelerates by impairing circulation. Sweating accelerates heat loss. Individuals with previous cold injury heat loss. Individuals with previous cold injury are more susceptible to reinjury.are more susceptible to reinjury.

Local cold injury produces a succession of Local cold injury produces a succession of changes. Skin sensation is lost at about 10°C changes. Skin sensation is lost at about 10°C (50°F). With further cooling, blood becomes (50°F). With further cooling, blood becomes more viscous, and blood vessels constrict and more viscous, and blood vessels constrict and begin to leak plasma. begin to leak plasma.

As skin cools further, freezing occurs and ice As skin cools further, freezing occurs and ice crystals form in the cells. This leads to cellular crystals form in the cells. This leads to cellular dehydration, shrinkage and damage to cell walls. dehydration, shrinkage and damage to cell walls. Blood vessels and nerves are the most Blood vessels and nerves are the most susceptible tissues.susceptible tissues.

Thawing results in additional injury, referred Thawing results in additional injury, referred to as reperfusion injury. to as reperfusion injury.

Blood flow becomes stagnant and contributes Blood flow becomes stagnant and contributes to further tissue hypoxia.to further tissue hypoxia.

There is also release of harmful substances There is also release of harmful substances from injured cells, leading to further cellular from injured cells, leading to further cellular damage. The degree of microvascular damage. The degree of microvascular damage determines whether circulation will damage determines whether circulation will recover or if the tissue will be lost. Tissue recover or if the tissue will be lost. Tissue damage is dependent upon the rate and damage is dependent upon the rate and duration of freezing and the rate of thawing.duration of freezing and the rate of thawing.

Refreezing after thawing causes more Refreezing after thawing causes more severe damage to the tissue involvedsevere damage to the tissue involved

Clinical Presentation and PrognosisClinical Presentation and Prognosis Symptoms are related to the severity of the Symptoms are related to the severity of the

injury. Initial symptoms of frostbite include injury. Initial symptoms of frostbite include coldness, numbness and a "clumsy" extremity.coldness, numbness and a "clumsy" extremity.

Thawing and reperfusion are often accompanied Thawing and reperfusion are often accompanied by intense pain. by intense pain.

Throbbing, burning or tingling sensations begin Throbbing, burning or tingling sensations begin in 2-3 days after rewarming and may persist for in 2-3 days after rewarming and may persist for weeks or months weeks or months

These symptoms are intensified by heat. These symptoms are intensified by heat. All patients experience some degree of All patients experience some degree of sensory loss, which can last for years and sensory loss, which can last for years and may become permanent. may become permanent.

There are two classes of frostbite injury: There are two classes of frostbite injury: mild/superficial (no tissue loss) and mild/superficial (no tissue loss) and severe/deep (loss of tissue). severe/deep (loss of tissue).

The initial appearance of frostbite may be The initial appearance of frostbite may be deceptively benign deceptively benign

Frozen tissue is numb, pale, hard and Frozen tissue is numb, pale, hard and waxy waxy

One cannot differentiate superficial from One cannot differentiate superficial from deep involvement at this stagedeep involvement at this stage

Following rapid rewarming, there is an Following rapid rewarming, there is an initial hyperemia.initial hyperemia.

Partial sensation returns until blisters form. Partial sensation returns until blisters form. Favorable prognostic signs include normal Favorable prognostic signs include normal sensation, color and warmth. sensation, color and warmth.

Edema should appear within three hours after Edema should appear within three hours after thawing. Lack of edema is an unfavorable thawing. Lack of edema is an unfavorable sign. sign.

Vesicles and bullae appear in 6-24 hours. Vesicles and bullae appear in 6-24 hours. Early formation of large, clear blisters that Early formation of large, clear blisters that extend to the tip of an affected digit is a good extend to the tip of an affected digit is a good indicator of tissue survival. Small, dark blebs indicator of tissue survival. Small, dark blebs that appear later and do not extend to the that appear later and do not extend to the digit tip indicate damage to underlying digit tip indicate damage to underlying vasculature and are associated with vasculature and are associated with subsequent tissue loss. subsequent tissue loss.

In severe frostbite, a black, hard, dry eschar In severe frostbite, a black, hard, dry eschar forms in 9-15 days postthaw.forms in 9-15 days postthaw.

It takes 22-45 days after thawing to know the It takes 22-45 days after thawing to know the true extent of tissue loss.true extent of tissue loss.

Most individuals will have persistent Most individuals will have persistent abnormalities of circulation even with minimal abnormalities of circulation even with minimal tissue loss. Long-term sequelae of frostbite tissue loss. Long-term sequelae of frostbite may include excessive sweating, pain, may include excessive sweating, pain, coldness, numbness, abnormal skin color and coldness, numbness, abnormal skin color and joint stiffness. These symptoms tend to be joint stiffness. These symptoms tend to be worse in cold temperatures.worse in cold temperatures.

Prehospital TreatmentPrehospital Treatment Treat hypothermia first, and avoid further heat Treat hypothermia first, and avoid further heat

loss from the patientloss from the patient

Provide supportive care for any suspected Provide supportive care for any suspected trauma, remove constrictive clothing trauma, remove constrictive clothing

At all costs, thawed tissue must not be At all costs, thawed tissue must not be allowed to refreeze. If a part is still frozen and allowed to refreeze. If a part is still frozen and rescue is imminent, keep the part frozen, rescue is imminent, keep the part frozen, unless warm water thaw is available and unless warm water thaw is available and there is no danger of refreezing. there is no danger of refreezing.

For example, if a victim with frostbitten feet For example, if a victim with frostbitten feet must walk to safety, it is better for him to must walk to safety, it is better for him to walk out on frozen feet (delaying walk out on frozen feet (delaying rewarming) rather than risk refreezing the rewarming) rather than risk refreezing the feet. feet.

Avoid excessive warming by hot water, Avoid excessive warming by hot water, campfire, car heater or any method >48°C campfire, car heater or any method >48°C (118°F), which causes burning of the frozen (118°F), which causes burning of the frozen part. Do not use friction massage, especially part. Do not use friction massage, especially with ice or snow.with ice or snow.

leave blisters intactleave blisters intact

prevent tissue damage by applying a loose, prevent tissue damage by applying a loose, sterile bandage.sterile bandage.

Splint the area and elevate the extremity.Splint the area and elevate the extremity.

PreventionPrevention Adequate food and fluid intake, staying dry Adequate food and fluid intake, staying dry

and avoiding fatigue are crucial to preventing and avoiding fatigue are crucial to preventing frostbite. Clothing and shelter are necessary frostbite. Clothing and shelter are necessary to provide a suitable micro-climate for the to provide a suitable micro-climate for the skin. Other important considerations include: skin. Other important considerations include:

Trip planningTrip planningWeather awarenessWeather awarenessProper equipmentProper equipmentAvoiding alcoholAvoiding alcoholAvoiding reflex vasoconstriction---cover all skinAvoiding reflex vasoconstriction---cover all skinUse of chemical warmersUse of chemical warmersCheck toes and fingers intermittentlyCheck toes and fingers intermittently

Buddy system for recognizing facial frostnip.Buddy system for recognizing facial frostnip.

HypothermiaHypothermia Hypothermia is defined as a core temperature Hypothermia is defined as a core temperature

<35°C (95°F)<35°C (95°F)

It occurs in all settings and in all seasons. It occurs in all settings and in all seasons. Urban settings account for most cases in the Urban settings account for most cases in the United States United States

Hypothermia is commonly associated with Hypothermia is commonly associated with concurrent trauma. Elderly patients are often concurrent trauma. Elderly patients are often found indoors with underlying illnesses that found indoors with underlying illnesses that can predispose them to hypothermia. can predispose them to hypothermia.

PathophysiologyPathophysiology

Humans are primarily tropically adaptedHumans are primarily tropically adapted

The hypothalamus acts as the body's The hypothalamus acts as the body's thermostat. Peripheral cooling of the blood thermostat. Peripheral cooling of the blood activates the hypothalamus, which leads activates the hypothalamus, which leads to an increase in metabolic rate, shivering to an increase in metabolic rate, shivering and peripheral vasoconstriction and peripheral vasoconstriction

humans' main adaptations are behavioral, humans' main adaptations are behavioral, such as putting on clothes or seeking a such as putting on clothes or seeking a warmer environmentwarmer environment

There are several mechanisms of heat There are several mechanisms of heat lossloss

Radiation is heat loss to the surrounding Radiation is heat loss to the surrounding environment and can be significant, environment and can be significant, depending on the amount of blood flow to depending on the amount of blood flow to the skin. It accounts for 60% of body heat the skin. It accounts for 60% of body heat loss at rest. A large amount of heat loss loss at rest. A large amount of heat loss comes from the head. Radiant heat loss is comes from the head. Radiant heat loss is reduced by wearing adequate clothing--reduced by wearing adequate clothing--especially a hat!especially a hat!

Conductive heat loss is heat transfer by Conductive heat loss is heat transfer by direct contact with an object. It is reduced direct contact with an object. It is reduced by insulation.by insulation.

Heat loss from evaporation (i.e. respiration Heat loss from evaporation (i.e. respiration and perspiration) is affected by the relative and perspiration) is affected by the relative humidity and ambient temperature of the humidity and ambient temperature of the environment. environment.

The body loses heat 25 times faster if the skin The body loses heat 25 times faster if the skin is wet. Evaporative loss is reduced by staying is wet. Evaporative loss is reduced by staying dry, using a vapor barrier and using mouth dry, using a vapor barrier and using mouth and nose moisture traps. and nose moisture traps.

Convection heat loss is determined by air Convection heat loss is determined by air movement over the skin (i.e. windchill) and is movement over the skin (i.e. windchill) and is reduced by a windproof layer.reduced by a windproof layer.

Predisposing factors to hypothermia can Predisposing factors to hypothermia can be divided into three groups. While there is be divided into three groups. While there is some overlap, most can be categorized as some overlap, most can be categorized as those that decrease heat production, those those that decrease heat production, those that increase heat loss and those that that increase heat loss and those that impair thermoregulation.impair thermoregulation.

Both young and old extremes of age are Both young and old extremes of age are susceptible to hypothermia from decreased heat susceptible to hypothermia from decreased heat production. Individuals with depleted glycogen production. Individuals with depleted glycogen stores or malnutrition have inadequate fuel to stores or malnutrition have inadequate fuel to keep warm. keep warm.

Endocrine insufficiencies (pituitary, adrenal and Endocrine insufficiencies (pituitary, adrenal and thyroid) and certain drugs that impair shivering thyroid) and certain drugs that impair shivering (alcohol) also play a role.(alcohol) also play a role.

Ways of increasing heat loss were Ways of increasing heat loss were described earlier. The most common described earlier. The most common iatrogenic causes include the use of cold iatrogenic causes include the use of cold IV fluids and prolonged exposure of the IV fluids and prolonged exposure of the patient for examination. patient for examination.

Burns and other skin disruption (i.e. Burns and other skin disruption (i.e. rashes) increase heat loss as well.rashes) increase heat loss as well.

Thermoregulation can be impaired by Thermoregulation can be impaired by diseases of the central or peripheral diseases of the central or peripheral nervous systems, such as CVAs, nervous systems, such as CVAs, neoplasms, Parkinson's, cord neoplasms, Parkinson's, cord transection or neuropathies. transection or neuropathies.

Certain metabolic derangements (i.e. Certain metabolic derangements (i.e. diabetes) or the pharmacologic effects diabetes) or the pharmacologic effects of certain drugs (i.e. benzodiazepines, of certain drugs (i.e. benzodiazepines, barbiturates, phenothiazines and cyclic barbiturates, phenothiazines and cyclic antidepressants) also lead to antidepressants) also lead to impairment.impairment.

Clinical PresentationClinical Presentation The body's physiologic responses to cooling and The body's physiologic responses to cooling and

clinical presentation vary widely between clinical presentation vary widely between individuals. Initially, there is an increase in the individuals. Initially, there is an increase in the metabolic rate and peripheral vasoconstrictionmetabolic rate and peripheral vasoconstriction

Maximal shivering occurs at 35°C (95°F) and is Maximal shivering occurs at 35°C (95°F) and is extinguished as the core temperature drops to extinguished as the core temperature drops to 31°-33°C (88°-92°F). 31°-33°C (88°-92°F).

Respiratory volume initially increases; Respiratory volume initially increases; however, with further cooling, it decreases. however, with further cooling, it decreases. Cardiovascular changes include initial Cardiovascular changes include initial tachycardia with progressive bradycardia tachycardia with progressive bradycardia and cardiac irritability.and cardiac irritability.

There is a linear decline in mean arterial There is a linear decline in mean arterial pressure, and cardiac output is <50% at pressure, and cardiac output is <50% at 25°C (77°F). The conduction system is 25°C (77°F). The conduction system is preferentially affected, which leads to a preferentially affected, which leads to a prolongation of all ECG intervals. The prolongation of all ECG intervals. The ECG may also show a J-wave or Osborn ECG may also show a J-wave or Osborn wave. wave.

The "hump" is present at the junction of The "hump" is present at the junction of the QRS complex and the ST-segment the QRS complex and the ST-segment and can mimic acute myocardial injury. and can mimic acute myocardial injury. Arrhythmias are common below 32° C Arrhythmias are common below 32° C (90°F). Atrial arrhythmias are usually (90°F). Atrial arrhythmias are usually innocuous. Ventricular fibrillation is innocuous. Ventricular fibrillation is typically induced, and asystole is part of typically induced, and asystole is part of the natural progression.the natural progression.

Higher cerebral functions start to decline Higher cerebral functions start to decline at core temperatures of 33°-35°C, and at core temperatures of 33°-35°C, and patients become unresponsive if cooling patients become unresponsive if cooling continues. The EEG is flat at 19°C (66°F). continues. The EEG is flat at 19°C (66°F).

Prehospital TreatmentPrehospital Treatment

Handle patients very gently, as the Handle patients very gently, as the myocardium may be irritable and iatrogenic myocardium may be irritable and iatrogenic ventricular fibrillation could result.ventricular fibrillation could result.

Prevent further heat loss with dry insulating Prevent further heat loss with dry insulating materials materials

If the patient is responsive, assume perfusion If the patient is responsive, assume perfusion is present. Palpation of peripheral pulses is is present. Palpation of peripheral pulses is difficult in a vasocontricted bradycardic patient difficult in a vasocontricted bradycardic patient

Monitor the patient closely, oxygenateMonitor the patient closely, oxygenate

Shivering artifact is a common problem. Shivering artifact is a common problem. Rewarming reverses vasoconstriction; if Rewarming reverses vasoconstriction; if the patient is not adequately fluid the patient is not adequately fluid resuscitated, this can lead to irreversible resuscitated, this can lead to irreversible and fatal shock, known as rewarming and fatal shock, known as rewarming shock. shock.

Field rewarming options include heated, Field rewarming options include heated, humidified oxygen, warmed IV fluids and humidified oxygen, warmed IV fluids and truncal heat application of hot water truncal heat application of hot water bottles or direct body-to-body heat. bottles or direct body-to-body heat.

Myth: A hypothermic patient is a Myth: A hypothermic patient is a metabolic icebox and is therefore stable metabolic icebox and is therefore stable and should not be rewarmed in the field.and should not be rewarmed in the field.

Fact: The patient is unstable and will Fact: The patient is unstable and will continue to rapidly lose heat to the continue to rapidly lose heat to the environment. Death is inevitable if environment. Death is inevitable if temperature declines to a certain value. temperature declines to a certain value. Rescuers should always attempt to at Rescuers should always attempt to at least stabilize the core body least stabilize the core body temperature.temperature.

Remember: "No body is dead until it is warm Remember: "No body is dead until it is warm and dead." and dead."

Initiate CPR in severe hypothermia unless Initiate CPR in severe hypothermia unless DNR status is documented and verified, DNR status is documented and verified, obvious lethal injuries are present, chest wall obvious lethal injuries are present, chest wall decompression is impossible, any signs of life decompression is impossible, any signs of life are present, or rescuers are endangered by are present, or rescuers are endangered by conditions. Apparent rigor mortis, dependent conditions. Apparent rigor mortis, dependent lividity and fixed dilated pupils are not reliable lividity and fixed dilated pupils are not reliable criteria to withhold CPR.criteria to withhold CPR.

Anticipate substandard activity of Anticipate substandard activity of resuscitation drugs in hypothermic patientsresuscitation drugs in hypothermic patients

In v-fib or v-tach, defibrillation rarely In v-fib or v-tach, defibrillation rarely succeeds below 30°C (86°F)succeeds below 30°C (86°F)

Atrial arrhythmias are typically innocent and Atrial arrhythmias are typically innocent and do not require treatment, as spontaneous do not require treatment, as spontaneous conversion is usual with rewarming. Expect a conversion is usual with rewarming. Expect a slow ventricular response in hypothermic slow ventricular response in hypothermic patients. Vasopressors can potentially cause patients. Vasopressors can potentially cause arrythmias and are ineffective if the patient is arrythmias and are ineffective if the patient is already maximally vasoconstricted.already maximally vasoconstricted.