Pediatrics

Hypothermia

OVERVIEW: What every practitioner needs to know

Are you sure your patient has hypothermia? What are the typical findings for this disease?

Hypothermia is a core body temperature below 35° Celsius (95° Fahrenheit). It can be the result of environmental reasons, most often accidental hypothermia, a primary metabolic disorder, or from therapeutic hypothermia. Severe hypothermia is generally harmful, however, in rare cases it may provide cerebral protection from anoxia during cardiac arrest.

Table I. Key Signs and Symptoms of Hypothermia at Different Core Body Temperatures

Table I.

Key Signs and Symptoms of Hypothermia at Different Core Body Temperatures
Severity Core Body Temperature Clinical Manifestations
Mild 32°-35° C Confusion, cold, pale skin, shivering and tachycardia
Moderate 28°-31.8° C Lethargy, reduced or absent shivering, bradycardia, decreased respiratory rate
Severe <28° C Obtundation or coma, no shivering, edematous skin, dilated and fixed pupils, bradycardia, hypotension, oliguria
Life Threatening <25° C Apnea, asystole

What other disease/condition shares some of these symptoms?

There are no diseases that mimic hypothermia. However, hypothermia may be a sign of multiple diseases or conditions. Environmental conditions, even in warm climates, can lead to hypothermia. A child exposed to wet, cool, or windy conditions is at risk for hypothermia. Trauma and resuscitation efforts may be associated with hypothermia because of environmental exposure, resuscitation with cold fluids, or not protecting the patient during transport.

Sepsis may present with hypothermia, especially in infants or immunocompromised patients. It also may be the presenting sign of child abuse. Submersion in cold water is becoming a more recognized form of child abuse.

What caused this disease to develop at this time?

Depending upon the etiology of the hypothermia, there are many predisposing factors that can be implicated.

Environmental or exposure to cold, wet, or windy weather put children at high risk for developing hypothermia. They have a small body mass to surface area ratio, limited glyogen stores which limit their ability to increase heat production in response to cold, and a lower level of cognitive ability, generally, to recognize and avoid a potentially dangerous environmental condition. Moreover, shivering in children produces less heat that in adults making it an ineffective heat producer in children.

History

If the etiology of the hypothermia is unknown, then pertinent history questions are critical. Specifically, questions related to environmental exposure are important. What was the duration of the exposure, the temperature, the wind speed, was the patient in cold water versus cold air. Cold water transfers heat much faster from the patient to the environment than when the patient is exposed to cold air. Therefore, hypothermia develops much faster if the patient is wet or was submerged in cold water.

Asking about trauma, exposure to infectious diseases, or a history of central hypothermia can also be helpful.

A patient who has a history of hypothalamic dysfunction may be predisposed to hypothermia and that history can help direct the treatment.

Physical Exam

The findings will often depend on the core body temperature. A specialized thermometer that can be placed in the patients esophagus, rectum, or bladder, should be used to record temperatures down to 25°C. A standard thermometer will not record temperatures below 35° C and therefore, may not be useful.

In mild hypothermia, patients may be confused and have findings that are typical of cold adaptation, such as cold pale skin from cutaneous vasoconstriction and brisk shivering.

In moderate hypothermia, shivering may be absent. These patients are often lethargic, bradycardic, bradypneic, with slurred speech, dilated or sluggish pupils. They may also have areas of frostbite. The areas most at risk are the fingers, toes, ears, and face and these should be inspected carefully.

Severe hypothermia may be a difficult diagnosis to make as many of the classic signs of hypothermia are no longer present. The skin may be flushed and the muscles become rigid as the temperature decreases. The muscle rigidity is secondary to the dysfunction of the actin-myosin bundles within the skeletal muscle. The pupils are fixed and dilated and respirations become more depressed. The cardiac output decreases secondary to sludging of the blood, depressed myocardial contractility, and hypovolemia because of vascular leak of fluid into extravascular spaces. This will lead to poor perfusion, weak distal and, eventually, central pulses.

The kidneys also become affected by the extreme low temperature and begin to lose concentrating ability. This leads to diuresis known as cold diuresis, and it contributes to the eventual circulatory collapse. The myocardium also becomes very irritable and can lead to severe or life threatening arrhythmias and, eventually, asystole.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Laboratory studies should be tailored to address the suspected cause of the hypothermia. In cases of children who are previously healthy and present with mild hypothermia secondary to environmental exposure, no routine laboratory or imaging studies are necessary.

Moderate, severe and/or life threatening hypothermia can lead to abnormalities in certain blood tests. Routine lab work should include a rapid serum glucose, serum electrolytes, serum blood urea nitrogen (BUN), and creatinine, lipse, a complete blood count (CBC), Prothrombin time (PT), partial thromboplastin time (PTT), and an international normalized ratio (INR). Blood type and crossmatch studies are necessary if the patient may need extracorporeal warming, and finally, arterial blood gas. Capillary gases should be avoided in these patients because peripheral circulation is poor and the gas may not accurately reflect the overall acid base status. For the same reason, peripheral pulse oximetry is not reliable and should not be relied upon for accurate data.

The results of these labs should be carefully reviewed. The serum electrolytes are important, specifically, because hyperkalemia is common in moderate to severe hypothermia. This may be secondary to the rhabdomyolysis from shivering. Serum creatinine may be elevated secondary to cold diuresis, poor cardiac output, or increased creatine kinase from rhabdomyolysis. These can lead to acute renal failure. A generalized coagulopathy may be seen in patients with hypothermia, but the coagulation labs, if run at normal body temperature, may be normal. Alternatively, the arterial blood gas should be run at normal body temperature and it can reveal a metabolic acidosis or a respiratory acidosis, or both.

Laboratory studies also may be indicated if the hypothermia is from an unknown etiology. In a child with multisystem trauma or child abuse, a urine dipstick for blood, liver enzymes, and type and crossmatch for blood products may be indicated. Further, in ill-appearing infants or children with hypothermia, sepsis should be suspected and blood, urine, and cerebral spinal fluid should be sent for culture and cell count. If the patient is at risk for substance or alcohol abuse then a serum or urine toxicology screen can be useful. Finally, a patient who is not responding to rewarming techniques, a thyroxine, thryoid stimulating hormone, adrenocorticoptropic hormone, and serum cortisol should be measured.

Would imaging studies be helpful? If so, which ones?

Routine imaging studies are done based on specific indications. In a previously healthy child with mild hypothermia secondary to environmental exposure, no imaging studies are indicated.

In patients with moderate to severe hypothermia an electrocardiography (EKG) is often indicated because of the risk of cardiac arrhythmias. If there is an abnormality, most patients will have a prominent J wave at the QRS-ST junction. These are called Osborn waves and are not specific for hypothermia. They also do not have any diagnostic or prognostic value in hypothermia. However, because the patient can have any type of abnormal rhythm in moderate to severe hypothermia an EKG is warranted.

In patients with pulmonary findings such as tachypnea, grunting, rales, or a cough, a history of chest trauma, or near drowning, a chest x-ray is indicated. Certainly, patients with multisystem trauma will require imaging and that decision should be based on the type and severity of the injury. Head trauma will often require computed tomography (CT) scan of the head as well as of the abdomen and pelvis if it is a significant trauma.

If child abuse is suspected, a skeletal survey, opthalmologic exam and, possibly, a CT of the head are indicated.

If you are able to confirm that the patient has hypothermia, what treatment should be initiated?

Are there some therapies that should be instituted immediately?

There are special considerations for patients with moderate to severe hypothermia that should be addressed. First, in children with severe hypothermia a pulse may be difficult to detect. The American Heart Association recommends assessing the patient for 30-45 seconds before initiating cardiopulmonary resuscitation efforts. With that in mind, as with any resuscitation, careful attention to the ABCs (Airway, Breathing, and Circulation) is the crucial first step in caring for any patient regardless of circumstances.

In the pre-hospital setting, and upon arrival to the hospital, accurate temperature measurement may be difficult. Removing the patient from the cold environment and placing them in a horizontal position is important to minimize the movement of peripheral blood into the central circulation.

If hypothermia is suspected, the providers should avoid rough handling of the patient, or exertion of the patient because of the extreme degree of myocardial irritability. Everything possible should be done to minimize heat loss during transport and in the hospital. Removal of wet clothing, gentle insulation of the patient with warm blankets, warming of the transport vehicle and warm IV fluids are all helpful. Be cautious in children with moderate to severe hypothermia, however. Active rewarming in transport should actually be avoided in these patients because of the cold afterdrop phenomenon. These patients should be monitored on a cardiorespiratory monitor to observe for any cardiac arrhythmias and abnormal breathing patterns.

Once these children arrive at the hospital, they should be handled very carefully, minimizing movement and keeping them horizontal. The rewarming techniques for moderate to severe hypothermia can take on various methods, but all patients can be given heated, humidified oxygen. The rewarming provided by this technique is limited because in most cases the temperature of the humidifer cannot exceed 41°C without modification. It does, however, help prevent further heat loss at that temperature. Additionally, having intravenous access in children with moderate to severe hypothermia is very helpful.

What about longer term treatment?

There are multiple techniques that can be used for longer term rewarming. Understanding them and when to use them is very important because of the irritability of the myocardium. There are three classes of rewarming methods available:

Passive rewarming: This involves removing wet or cold clothing and applying dry insulation like blankets or sleeping bags in a warm environment. This type of rewarming relies on the patients ability to generate their own heat and does not offer any additional heat to the patient. This can be used in conjunction with active rewarming, even in cases of mild hypothermia.

Active Rewarming can be subdivided into two categories, active external rewarming and active internal rewarming:

-Active external rewarming implies that an external source of heat is being applied to the patient. This can be in the form of forced air rewarming, radiant heat, or direct heat from heating pads or chemical heat packs.

-Active internal rewarming refers to methods used to heat the patient internally. This can be done in several ways. In mild cases of hypothermia, non-invasive techniques like providing warmed oral fluids and heated humidifed oxygen are helpful. Warm intravenous normal saline is also considered a non-invasive technique. Using room temperature fluids may worsen hypothermia and should be avoided. More invasive techniques such as heated saline lavage of the pleural space, bladder, stomach, or peritoneum are used in patients with severe hypothermia or an inadequate response to initial non-invasive forms of rewarming.

Extracorporeal Techniques of Rewarming:

These are reserved for children with severe or life threatening hypothermia with absent circulation or in children for whom other warming techniques are not working. These types of techniques may include cardiac bypass or extracorporeal membrane oxygenation (seeTable II. Rewarming Techniques).

Table II.

Rewarming Techniques
Mild hypothermia Active external rewarming with blankets, warm room, warm IV saline, warm oral liquids
Moderate hypothermia Active external rewarming with forced warm air being the preferred method
Severe hypothermia:
Circulation intact Left pleural lavage or forced air rewarming, plus all the above methods except oral liquids
Circulation absent Extracorporeal rewarming if available. If not, continued left pleural lavage, bladder and stomach lavage. Careful to protect the airway when putting warm liquids into the stomach.

Some additional considerations for treatment of the patient with hypothermia

Vascular access in patients with hypothermia can be a challenge. If a peripheral line cannot be placed that is at least a 22 gauge needle, then an intraosseous line should be considered.

Fluid resuscitation should follow the rewarming techniques above. Often patients with moderate to severe hypothermia are severely hypovolemic due to volume shifts. Initial normal saline bolus should be at 20ml/kg of body weight. Additional fluid resuscitation should follow pediatric advanced life support (PALS) protocols. Knowing whether the fluid resuscitation efforts are successful can be difficult. If possible, a central venous wedge pressure can be helpful, but should be inserted via the femoral vein to avoid interacting with the irritable myocardium and causing ventricular fibrillation.

Drug therapy is often ineffective in patients with hypothermia. Drugs for cardiac arrhyhmias should be withheld until the patient is rewarmed to prevent accumulation of these drugs which can cause potentially harmful effects. The only drug that should not be withheld is glucose. If there is a suspicion or known hypoglycemia, IV glucose should be given. If hyperglycemia results then insulin can be given if it persists once the patient has been rewarmed. Glucose often returns to normal levels without insulin at normal body temperatures.

There are certain cardiac rhythms that are more common in moderate to severe hypothermia. Table III describes the rhythm and what should be done to manage it.

Table III.

Management of Abnormal Cardiac Rhythms in Hypothermia
Cardiac Rhythm Perfusion Action Plan
Bradycardia (1st Degree AV Block, atrial fibrillation with slow ventricular response) Yes Rewarm patient.Cardiac pacing is ineffective.IV antiarrhythmic medications are discouraged.These rhythms are adequate for maintaining oxygen delivery.
Ventricular Fibrillation with severe hypothermia No One attempt at debrillation - if unsuccessful, delay further attempts until the core temperature reaches >28° C.In general IV resuscitation meds are discouraged.IV dextrose should be administered if there is known or suspected hypoglycemia.
Ventricular Fibrillation with moderate hypothermia No Debrillation and resuscitation medications are indicated.Spacing out interventions to between 4-6 minutes rather than between 2-3 minutes until the patient is rewarmed to 32°-34°C is thought to prevent excess medication accumulation and negative effects once the patient is rewarmed.
Asystole or Pulseless electrical activity No If hypothermia is severe, these children should be intubated, receive chest compressions and extracorporeal warming.IV resuscitation meds are not indicated, however IV dextrose is indicated.If hypothermia is moderate, children should receive IV medications according to PALS protocol.In most cases resuscitation efforts should continue until the child's core temperature is >34°C.

What are the adverse effects associated with each treatment option?

Despite gentle rewarming in the field, patients will often arrive at the hospital colder than when they left the scene. This is referred to as "cold after drop". During initial rewarming, the patient redirects the cold blood centrally if the patient has intact cirulation which leads to continued cooling of the patient.

Active external rewarming with heating pads or chemical heat packs can cause burns in areas where the skin is underperfused. Providers should carefully observe these areas to prevent this from occurring. Additionally, the patient is also at risk for cold after drop, which is a significant morbidity of active external rewarming. In patients with moderate to severe hypothermia, this redirection of cold blood to the central circulation can cause cardiac arrhythmias and hypotension. To prevent this, the trunk should be warmed first.

Rewarming shock is another potential adverse effect associated with treatment of hypothermia. Hypovolemia, cold diuresis, and myocardial depression all contribute to rewarming shock.

Cardiac arrhythmias are a significant cause of morbidity and mortality during rewarming of a hypothermic patient. Taking care not to move the patient too much helps to prevent peripherally cold blood to move centrally which can aggravate the irritable myocardium leading to a cardiac arrhythmia. Similarly, inserting a chest tube for warm left sided pleural lavage increases the risk of the chest tube irritating the myocardium causing a ventricular arrhythmia.

Finally, any form of extracorporeal warming of the patient has inherent risks. A large bore central access must be maintained for both incoming and outgoing blood. This presents a problem for patients with coagulopathy related to their hypothermia. Infection is also a risk, although less so in the short term. This type of therapy may also increase the risk of stroke or other neurologic sequelae. Great care should be taken to minimize the risk of these adverse effects of treatment.

What are the possible outcomes of hypothermia?

The possible outcomes of hypothermia depend upon the degree of hypothermia, the duration of the resuscitation and the methods used to rewarm the patient. There are patients who fail to respond to aggressive rewarming techniques and in those cirumstances, other etiologies for the hypothermia should be investigated and treated appropriately. For example, sepsis requires broad spectrum antibiotics, hypoglycemia, or hyponatremia require the appropriate intravenous fluids to be administered. Occasionally, adrenal insufficiency may be the reason for the unresponsiveness and empiric treatment with intravenous hydrocortisone would be indicated.

If the patient responds to the rewarming techniques, then in most cases the patients will recover. The morbidity associated with hypothermia depends upon the duration of the resuscitation. There are many case reports as well as a small case series in which patients with severe hypothermia and cardiac arrest had no serious long term neurologic sequelae. However, at the time of the admission for hypothermia, giving families prognostications about how the patient will do is not recommended because it could be misleading. Many patients with moderate to severe hypothermia make a full recovery. Others have some degree of neurologic sequelae. However, there is no way to predict from the physical exam at the time of presentation what the outcome will be. Additionally, complete neurologic recovery may take several months.

What will you tell the family about risks/benefits of the available treatment options?

The family should be told about the risks previously described. The risk/benefit ratio, however, is heavily weighted on the side of benefit. Patients with severe hypothermia will not survive without many of the rewarming techniques. Therefore, there is no "wait and see" option for moderate and severe hypothermia. Immediate rewarming of the patient is always indicated unless the patient has other injuries that are not compatible with life.

What causes this disease and how frequent is it?

  • The primary cause of hypothermia in pediatric patients is accidental exposure. In cases in which accidental exposure is not the etiology and the hypothermia is due to other causes the frequency is dependent upon the disease process.

    • Incidence, seasonal variation, gender differences

      • According to the Centers for Disease Control (CDC), in the United States from 1979--2002, a total of 16,555 deaths were attributed to hypothermia.

      • The death rate from hypothermia is approximately 0.2-0.4 per 100,000 population.

      • Most cases of hypothermia in the United States are in males, however, the death rate is the same in both males and females.

      • The winter months have a higher incidence of hypothermia, but it can be seen in the Fall and Spring months as well. Additionally, where there is cold water, the risk of hypothermia is always possible.

      • States with the greatest overall death rates for hypothermia in 2002 were Alaska, New Mexico, North Dakota, and Montana.

      • States with rapid temperature changes or a significant difference between daytime and nighttime temperatures, like North and South Carolina also report hypothermia related deaths.

How do these pathogens/genes/exposures cause the disease?

Generally speaking, exposure to cold is the primary cause of hypothermia. For children, hypothermia is a greater risk than for adults because of their small body mass to surface area ratio. This leads to increased heat loss in cold environments. Additionally, they do not shiver as much or as effectively as adults and they have lower glycogen stores which normally promotes heat production in response to the cold.

Pathophysiologically, the body responds to cold differently at different temperatures. In mild hypothermia, the body begins to shiver, vasoconstrict the peripheral vasculature and increases metabolism to produce heat. As the temperature decreases, so does the body's ability to combat the cold. Respiratory function is depressed, there is a decrease in metabolism, circulatory instability and insufficiency with vasodilation and hypovolemia. Additionally, altered mental status is noted and the patient may have confusion, lethargy and slurred speech.

As the body temperature drops even further, the metabolic machinery of the body is suppressed or arrested. Metabolism slows by approximately 6% for every one degree Celsius of body temperature decrease. In moderate to severe hypothermia the metabolic rate is approximately half of the normal rate. At this temperature, all body functions begin to fail including circulation, ventilation, and the central nervous sytem.

There is some literature that severe hypothermia can be cerebroprotective. In other words, the central nervous system may be protected from the effects of hypoxia because of the depressed metabolic rate in severe hypothermia. This protection is not seen in all patients, especially if there was a hypoxic event prior to the development of hypothermia.

What complications might you expect from the disease or treatment of the disease?

Complications from the treatment of hypothermia has been previously addressed. In terms of the hypothermia itself, the complications are related to the damage done by the cardiac irritability. Often there are neurologic consequences that may improve over several months. If there was an anoxic event patients may have difficulty with their speech, their fine or gross motor skills, or memory. Physical therapy and speech and/or occupational therapy may help the patient gain back their skills over the ensuing months.

How can hypothermia be prevented?

Hypothermia from accidental exposure can be prevented in several ways. First, appropriate dress is critical to avoid hypothermia. The CDC recommends that children should dress warmly and stay dry. They recommend that children wear a hat, scarf or knit mask to cover their face and mouth, sleeves that are snug at the wrist, mittens (not gloves), water-resistant coat and boots and several layers of loose fitting clothing. Ensuring that the outer layer of clothing is tightly woven and, preferably, wind resistant will reduce body heat loss caused by the wind. Wet clothing cools the body quickly and removing wet clothing quickly is important. it is also important not to ignore shivering. This is the first sign that the body is losing heat. Shivering should be an indication to move indoors and out of the elements.

Alcohol and drug use can also increase the likelihood that a person does not recognize the signs of mild hypothermia. Children also may not have the cognitive maturity to recognize when they need to move indoors. Adult supervision while children are playing outdoors in cold temperatures is recommended. Further, swimming in cold water should also be monitored closely. If signs of hypothermia begin to appear such as shivering, exhaustion, bright red and cold skin, or drowsiness, the child should be moved indoors and rewarming should begin.

What is the evidence?

"2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Part 10.4: Hypothermia". Circulation. vol. 112. 2005. pp. IV-136.

(General review)

Farstad, M, Andersen, KS, Koller, ME, Grong, K, Segadal, L, Husby, P. "Rewarming from accidental hypothermia by extracorporeal circulation: a retrospective study". Eur J Cardiothorac Surg.. vol. 20. 2001. pp. 58-64.

(Patients with accidental hypothermia combined with circulatory arrest or severe circulatory failure were rewarmed to normothermia by use of extracorporeal circulation (ECC) protocol. Those with non-asphyxiated deep accidental hypothermia were found to have a reasonable prognosis. In contrast, drowned patients with secondary hypothermia had a very poor prognosis. The authors recommend that patients meeting the former criteria be agressively rewarmed before further therapeutic decisions are made.)

Larach, MG. "Accidental hypothermia". Lancet.. vol. 345. 1995. pp. 493-498.

(An early review of the factors influencing the decision to initiate or continue resuscitation once a hypothermic patient arrives in the ED, and the methods for rewarming.)

Romet, TT. "Mechanism of afterdrop after cold water immersion". J Appl Physiol.. vol. 65. 1988. pp. 1535-1538.

(Reviews pathophysiology in cold water immersion injury.)

Hughes, A, Riou, P, Day, C. "Full neurological recovery from profound (18.0 degrees C) acute accidental hypothermia: successful resuscitation using active invasive rewarming techniques". Emerg Med J. vol. 24. 2007 Jul. pp. 511-2.

(A protocol for rapid rewarming of hypothermic patients.)

Alfonzo, A, Lomas, A, Drummond, I, McGugan, E. "Survival after 5-hour resuscitation attempt for hypothermic cardiac arrest using CVVH for extracorporeal rewarming". Nephrol Dial Transplant. vol. 24. 2009 Mar. pp. 1054-6.

(A protocol for rapid rewarming of hypothermic patients.)

Ongoing controversies regarding etiology, diagnosis, treatment

The duration of attempted resuscitation of the accidental hypothermia victim remains controversial. The references by Hughes et al and Alfonzo et al (above) are central to this debate.

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