Hypothermia
What is hypothermia?
The body maintains a relatively stable temperature whereby heat production is balanced by heat loss. Normally, the core body temperature (when measured rectally) is 98.6 degrees F or 37 degrees C. When the outside environment gets too cold or the body's heat production decreases, hypothermia occurs (hypo=less + thermia=temperature). Hypothermia is defined as having a core body temperature less than 95 degrees F or 35 degrees C.
Body temperature is controlled in the part of the brain called the hypothalamus, which is responsible for recognizing alterations in the body temperature and responding appropriately. The body produces heat through the metabolic processes in cells that support vital body functions. Most heat is lost at the skin surface by convection, conduction, radiation, and evaporation. If the environment gets colder, the body may need to generate more heat by shivering (increasing muscle activity that promotes heat formation). But if heat loss is greater than the body's ability to make more, then the body's core temperature will fall.
As the temperature falls, the body shunts blood away from the skin and exposure to the elements. Blood flow is increased to the vital organs of the body including the heart, lungs, kidney, and brain. The heart and brain are most sensitive to cold, and the electrical activity in these organs slows in response to cold. If the body temperature continues to decrease, organs begin to fail, and eventually death will occur.
Medical uses of hypothermia
Cooling patients as part of their medical care is called induced or therapeutic hypothermia. While there is potential benefit of this practice for many conditions, at present, medical hypothermia is most often used in patients who have been resuscitated from cardiac arrest.
Medical scientists have shown that in patients who survived episodes of cardiac arrest due to ventricular fibrillation or ventricular tachycardia, cooling the body to 93.2 F (34 C) for 12-24 hours was associated with better survival rates and better neurologic outcomes.
The body maintains a relatively stable temperature whereby heat production is balanced by heat loss. Normally, the core body temperature (when measured rectally) is 98.6 degrees F or 37 degrees C. When the outside environment gets too cold or the body's heat production decreases, hypothermia occurs (hypo=less + thermia=temperature). Hypothermia is defined as having a core body temperature less than 95 degrees F or 35 degrees C.
Body temperature is controlled in the part of the brain called the hypothalamus, which is responsible for recognizing alterations in the body temperature and responding appropriately. The body produces heat through the metabolic processes in cells that support vital body functions. Most heat is lost at the skin surface by convection, conduction, radiation, and evaporation. If the environment gets colder, the body may need to generate more heat by shivering (increasing muscle activity that promotes heat formation). But if heat loss is greater than the body's ability to make more, then the body's core temperature will fall.
As the temperature falls, the body shunts blood away from the skin and exposure to the elements. Blood flow is increased to the vital organs of the body including the heart, lungs, kidney, and brain. The heart and brain are most sensitive to cold, and the electrical activity in these organs slows in response to cold. If the body temperature continues to decrease, organs begin to fail, and eventually death will occur.
Medical uses of hypothermia
Cooling patients as part of their medical care is called induced or therapeutic hypothermia. While there is potential benefit of this practice for many conditions, at present, medical hypothermia is most often used in patients who have been resuscitated from cardiac arrest.
Medical scientists have shown that in patients who survived episodes of cardiac arrest due to ventricular fibrillation or ventricular tachycardia, cooling the body to 93.2 F (34 C) for 12-24 hours was associated with better survival rates and better neurologic outcomes.
How is hypothermia diagnosed?
Usually the diagnosis of hypothermia is evident because of circumstances. The patient is found outside in the cold, and either the patient or a companion can explain the situation. Sometimes, it is less apparent, especially if the patient is found indoors and is confused.
The body core temperature needs to be measured; this may be done with a special rectal thermometer that is designed for very low readings or with a bladder catheter equipped with a temperature probe. Oral or ear temperatures are not accurate in very cold patients.
Aside from diagnosing hypothermia, the underlying cause needs to be ascertained. While some causes may be readily apparent, there may be confounding factors. Intoxicated patients may have fallen and sustained a head injury. The elderly patient may have diabetes and have a low blood sugar. While it is important to treat the low temperature, the individual medical history of the patient needs to be considered and appropriate diagnostic tests performed to rule out any associated injuries or conditions.
How is hypothermia treated?
Care for the hypothermic patient begins when the person is found.
One axiom that continues to be followed in emergency medical care is that a patient is not dead until they are "warm and dead." Vital signs like breathing, heartbeat, and blood pressure may be difficult to detect in a severely hypothermic patient, and often efforts are made to try prolonged resuscitation until the patient is warmed. Occasional stories are reported in the press about patients, especially children, who have been resuscitated from severe hypothermia due to immersion in cold water
Usually the diagnosis of hypothermia is evident because of circumstances. The patient is found outside in the cold, and either the patient or a companion can explain the situation. Sometimes, it is less apparent, especially if the patient is found indoors and is confused.
The body core temperature needs to be measured; this may be done with a special rectal thermometer that is designed for very low readings or with a bladder catheter equipped with a temperature probe. Oral or ear temperatures are not accurate in very cold patients.
Aside from diagnosing hypothermia, the underlying cause needs to be ascertained. While some causes may be readily apparent, there may be confounding factors. Intoxicated patients may have fallen and sustained a head injury. The elderly patient may have diabetes and have a low blood sugar. While it is important to treat the low temperature, the individual medical history of the patient needs to be considered and appropriate diagnostic tests performed to rule out any associated injuries or conditions.
How is hypothermia treated?
Care for the hypothermic patient begins when the person is found.
- First aid should be initiated.
- The patient should be removed from the cold environment and placed in a warm shelter away from the wind. Wet clothing should be removed and replaced with a warm, dry covering including head covering.
- Emergency medical services should be activated (call 911 if available) as soon as possible.
- The patient's breathing should be monitored, and if it becomes dangerously slow or stops, CPR should be initiated.
- Rough handling or jerking of the patient should be minimized if the person is lethargic or unconscious. This may cause an irritable heart to develop electrical abnormalities such as ventricular fibrillation.
- Rewarming should be started by applying warm compresses to the chest, neck, and groin. Hot water should not be used. Because there may be associated frostbite, direct heat should not be applied to the body. Instead, warm blankets and body to body contact may be needed as a first aid measure.
- The severity of hypothermia and the patient's mental status and ability to function will determine what further treatment is necessary. Passive rewarming with warm clothing in a warm environment may be all that is required for a conscious person who is shivering.
- Active rewarming may be considered for those who are colder, showing signs of confusion, or have other medical conditions that need attention. Warmed intravenous fluids, warming blankets, and warmed humidified air may be provided in the hospital.
- More aggressive core rewarming may include infusing warm fluids into the stomach or bladder, irrigating warm solutions into the chest or abdominal cavity, and in some situations, placing the patient on dialysis or heart bypass to rewarm the body.
One axiom that continues to be followed in emergency medical care is that a patient is not dead until they are "warm and dead." Vital signs like breathing, heartbeat, and blood pressure may be difficult to detect in a severely hypothermic patient, and often efforts are made to try prolonged resuscitation until the patient is warmed. Occasional stories are reported in the press about patients, especially children, who have been resuscitated from severe hypothermia due to immersion in cold water
What causes hypothermia?
Hypothermia most often occurs because of prolonged exposure to cold weather. Inadequate clothing for conditions may not provide enough insulation for the body to prevent heat loss. Immersion in water hastens hypothermia, and just a few minutes in cold water may be fatal.
What are the risk factors for hypothermia?
There are numerous factors that increase the risk of hypothermia:
Hypothermia most often occurs because of prolonged exposure to cold weather. Inadequate clothing for conditions may not provide enough insulation for the body to prevent heat loss. Immersion in water hastens hypothermia, and just a few minutes in cold water may be fatal.
What are the risk factors for hypothermia?
There are numerous factors that increase the risk of hypothermia:
- Age: The very young and very old may be less able to generate heat. The elderly with underlying medical conditions such as hypothyroidism or Parkinson's disease that limit the ability of the body to regulate temperature are less able to generate heat. Infants don't generate heat as efficiently, and with their relatively large head size compared to the body, they are at risk for increased heat loss by radiation.
- Mental status: Impaired judgment and mental function can lead to cold exposure. Patients with Alzheimer's disease are prone to wander and become exposed to the elements.
- Substance abuse: Alcohol and drug abuse increase the risk of hypothermia in two ways. First, impaired judgment can lead to cold exposure. Additionally, alcohol and similar drugs can dilate blood vessels near the skin (vasodilation) and decrease the efficiency of the shivering mechanism, both of which decrease the body's ability to compensate for cold exposure.
- Medical conditions: Underlying medical conditions can also lead to accidental hypothermia.
- Patients with hormonal abnormalities (thyroid, adrenal, pituitary), and those with peripheral neuropathy (due to diabetes or other conditions) or may be less able to feel the cold and generate a shivering response.
- Patients with spinal cord injuries, similarly, may not be able to adequately shiver.
- Patients who have suffered strokes or brain tumors may have impaired thermal regulation centers in the brain.
- Overwhelming infection and sepsis may both present with a lowered temperature instead of fever. People with diabetes who have very low blood sugar can appear unconscious and very cold.
- Patients with hormonal abnormalities (thyroid, adrenal, pituitary), and those with peripheral neuropathy (due to diabetes or other conditions) or may be less able to feel the cold and generate a shivering response.
- Medications: Some medications can increase the risk of hypothermia by limiting the shivering mechanism including some psychiatric medications
What are the signs and symptoms of hypothermia?
The body starts to slow as the temperature drops. Aside from the cold that is felt and the shivering that may occur, mental function is most affected initially. A particular danger of hypothermia is that it develops gradually, and since it affects thinking and reasoning, it may go unnoticed.
The heart is subject to abnormal electrical rhythms as hypothermia progresses. Ventricular fibrillation, a disorganized rhythm in which the heart is unable to pump, may occur at core temperatures below 82.4 F (28 C). This is one type of cardiac arrest.
Hypothermia Symptoms by Body Temperature Celsius Fahrenheit Description Symptoms 37 98.6 No hypothermia No hypothermia Below 35 95 Definition of hypothermia N/A 32 to 35 89.6 to 95 Mild hypothermia Shivering
Lethargy, apathy, confusion
Rapid heart rate 28 to 32 82.4 to 89.6 Moderate hypothermia Shivering stops
Increased confusion or delirium
Slowing heart rate; may be come irregular Below 28 Below 82.4 Severe hypothermia Coma
Ventricular fibrillation
May appear deceased 20 68 Brain activity stops
The body starts to slow as the temperature drops. Aside from the cold that is felt and the shivering that may occur, mental function is most affected initially. A particular danger of hypothermia is that it develops gradually, and since it affects thinking and reasoning, it may go unnoticed.
- Initial hunger and nausea will give way to apathy as the core body temperature drops.
- This is followed by confusion, lethargy, slurred speech, loss of consciousness, and coma.
- Often the affected person will lie down, fall asleep, and die. In some cases, the patient will paradoxically remove their clothes just before this occurs.
The heart is subject to abnormal electrical rhythms as hypothermia progresses. Ventricular fibrillation, a disorganized rhythm in which the heart is unable to pump, may occur at core temperatures below 82.4 F (28 C). This is one type of cardiac arrest.
Hypothermia Symptoms by Body Temperature Celsius Fahrenheit Description Symptoms 37 98.6 No hypothermia No hypothermia Below 35 95 Definition of hypothermia N/A 32 to 35 89.6 to 95 Mild hypothermia Shivering
Lethargy, apathy, confusion
Rapid heart rate 28 to 32 82.4 to 89.6 Moderate hypothermia Shivering stops
Increased confusion or delirium
Slowing heart rate; may be come irregular Below 28 Below 82.4 Severe hypothermia Coma
Ventricular fibrillation
May appear deceased 20 68 Brain activity stops
How is hypothermia diagnosed?
Usually the diagnosis of hypothermia is evident because of circumstances. The patient is found outside in the cold, and either the patient or a companion can explain the situation. Sometimes, it is less apparent, especially if the patient is found indoors and is confused.
The body core temperature needs to be measured; this may be done with a special rectal thermometer that is designed for very low readings or with a bladder catheter equipped with a temperature probe. Oral or ear temperatures are not accurate in very cold patients.
Aside from diagnosing hypothermia, the underlying cause needs to be ascertained. While some causes may be readily apparent, there may be confounding factors. Intoxicated patients may have fallen and sustained a head injury. The elderly patient may have diabetes and have a low blood sugar. While it is important to treat the low temperature, the individual medical history of the patient needs to be considered and appropriate diagnostic tests performed to rule out any associated injuries or conditions.
How is hypothermia treated?
Care for the hypothermic patient begins when the person is found.
One axiom that continues to be followed in emergency medical care is that a patient is not dead until they are "warm and dead." Vital signs like breathing, heartbeat, and blood pressure may be difficult to detect in a severely hypothermic patient, and often efforts are made to try prolonged resuscitation until the patient is warmed. Occasional stories are reported in the press about patients, especially children, who have been resuscitated from severe hypothermia due to immersion in cold water.
Usually the diagnosis of hypothermia is evident because of circumstances. The patient is found outside in the cold, and either the patient or a companion can explain the situation. Sometimes, it is less apparent, especially if the patient is found indoors and is confused.
The body core temperature needs to be measured; this may be done with a special rectal thermometer that is designed for very low readings or with a bladder catheter equipped with a temperature probe. Oral or ear temperatures are not accurate in very cold patients.
Aside from diagnosing hypothermia, the underlying cause needs to be ascertained. While some causes may be readily apparent, there may be confounding factors. Intoxicated patients may have fallen and sustained a head injury. The elderly patient may have diabetes and have a low blood sugar. While it is important to treat the low temperature, the individual medical history of the patient needs to be considered and appropriate diagnostic tests performed to rule out any associated injuries or conditions.
How is hypothermia treated?
Care for the hypothermic patient begins when the person is found.
- First aid should be initiated.
- The patient should be removed from the cold environment and placed in a warm shelter away from the wind. Wet clothing should be removed and replaced with a warm, dry covering including head covering.
- Emergency medical services should be activated (call 911 if available) as soon as possible.
- The patient's breathing should be monitored, and if it becomes dangerously slow or stops, CPR should be initiated.
- Rough handling or jerking of the patient should be minimized if the person is lethargic or unconscious. This may cause an irritable heart to develop electrical abnormalities such as ventricular fibrillation.
- Rewarming should be started by applying warm compresses to the chest, neck, and groin. Hot water should not be used. Because there may be associated frostbite, direct heat should not be applied to the body. Instead, warm blankets and body to body contact may be needed as a first aid measure.
- The severity of hypothermia and the patient's mental status and ability to function will determine what further treatment is necessary. Passive rewarming with warm clothing in a warm environment may be all that is required for a conscious person who is shivering.
- Active rewarming may be considered for those who are colder, showing signs of confusion, or have other medical conditions that need attention. Warmed intravenous fluids, warming blankets, and warmed humidified air may be provided in the hospital.
- More aggressive core rewarming may include infusing warm fluids into the stomach or bladder, irrigating warm solutions into the chest or abdominal cavity, and in some situations, placing the patient on dialysis or heart bypass to rewarm the body.
One axiom that continues to be followed in emergency medical care is that a patient is not dead until they are "warm and dead." Vital signs like breathing, heartbeat, and blood pressure may be difficult to detect in a severely hypothermic patient, and often efforts are made to try prolonged resuscitation until the patient is warmed. Occasional stories are reported in the press about patients, especially children, who have been resuscitated from severe hypothermia due to immersion in cold water.
When should I call the doctor for hypothermia?
In parts of the country where a cold environment is a way of life, many people have minor exposures to the elements and do not need to seek medical care.
Because the brain is so sensitive to cold, medical care should be accessed if the mental status of the patient is affected. This is manifested by a wide range of behaviors, from the person who is mildly confused to the patient who is comatose. As well, it is important to remember that there may be an underlying medical condition that led to the hypothermia that may need to be addressed.
If there is any uncertainty, emergency medical services should be activated (call 911 if it is available).
Can hypothermia be prevented?
While medical emergencies can occur in association with hypothermia (for example, people with diabetes who develop very low blood sugar), most cases of hypothermia are preventable with good planning and good judgment.
In parts of the country where a cold environment is a way of life, many people have minor exposures to the elements and do not need to seek medical care.
Because the brain is so sensitive to cold, medical care should be accessed if the mental status of the patient is affected. This is manifested by a wide range of behaviors, from the person who is mildly confused to the patient who is comatose. As well, it is important to remember that there may be an underlying medical condition that led to the hypothermia that may need to be addressed.
If there is any uncertainty, emergency medical services should be activated (call 911 if it is available).
Can hypothermia be prevented?
While medical emergencies can occur in association with hypothermia (for example, people with diabetes who develop very low blood sugar), most cases of hypothermia are preventable with good planning and good judgment.
- Wear appropriate clothing for the weather.
- Prepare for the worst when enjoying an outdoor activity if cold weather is a possibility. If choosing to drink alcohol, make certain there is a sober person who will be responsible for your safety.
- For the elderly and the poor who may not have adequate home heating in the winter, communities should insure that safe housing is available. Shut-ins should have routine social service or family contacts.
- Hypothermia can be defined as a core body temperature less than 95 F or 35 C
- Shivering is one way the body generates heat to combat falling temperatures
- Brain function decreases as body temperature falls; this happens gradually and may go unnoticed.
- At low body temperatures, the heart's electrical system may become irritable and cause a fatal heart rhythm
- Treatment begins with removing the patient from the cold environment and providing warmth. Wet clothing should be removed as soon as possible and replaced with warm, dry covering.
- When in doubt, activate emergency medical services (call 911)
- Almost all cases of hypothermia are preventable.
Hypothermia is having a body core temperature of less than 35 C or 95 F. Most causes of hypothermia are preventable. Risk factors for hypothermia include age, mental status, substance abuse, medical conditions, and medications. Symptoms of hypothermia generally depend upon the severity of the condition. Treatment depends upon the severity of hypothermia. If not treated early, hypothermia can lead to cardiac arrest, coma, or death.
