Hypothermia in children: Management

INTRODUCTION — 

This article discusses the treatment of hypothermia in children. The clinical manifestations of hypothermia in children, neonatal hypothermia, and frostbite are discussed separately. (See "Hypothermia in children: Clinical manifestations and diagnosis" and "Overview of short-term complications in preterm infants", section on 'Hypothermia' and "Frostbite: Acute care and prevention".)

Such treatment may be challenging, even for advanced care teams, but can also be unexpectedly rewarding. In this topic, we emphasize:

●The hazards of missed diagnosis and too-early declaration of death

●The key role of core body temperature measurement

●The ways in which cold alters critical decisions to withhold, withdraw, or prolong treatment

●The central importance of effective rewarming

●The impact of hypothermia on resuscitation and supportive care

DEFINITION OF HYPOTHERMIA — 

Hypothermia is defined as a core body temperature below 35°C (95°F). The stage of hypothermia, defined by core temperature, has a major impact on both recognition and treatment. These stages may be broadly viewed as compensation, decompensation, and finally failure of the body's defenses against cold (table 1). Typical definitions are as follows [1-4]:

●Mild – Core temperature 32 to 35°C (90 to 95°F)

●Moderate – Core temperature 28 to 32°C (82 to 90°F)

●Severe – Core temperature below 28°C (82°F)

Some experts define a core temperature <25°C (77°F) as profound hypothermia [3].

Published temperature cutoffs vary slightly [4]; all cutoffs are approximate because of imprecise measurement and individual patient variation.

Symptoms and signs can be misleading in critical care decisions. Core body temperature should be measured as soon as possible. Clinical staging schemes note that the declaration of death should not be made without accurate measurement of core body temperature [3,5,6]. (See 'Prehospital considerations' below.)

IMPACT ON TREATMENT DECISIONS — 

The presence of hypothermia with a core temperature <32°C (90°F) alters typical decisions to withhold or terminate treatment. At these temperatures, suspended metabolism may protect against hypoxia. We would resuscitate and rewarm all children with moderate or severe hypothermia unless clearly lethal injuries are present. In pulseless patients with severe hypothermia (core temperature <28°C [82°F]), clinicians must avoid the premature declaration of death.

REWARMING CLASSIFICATION AND DEFINITIONS — 

Rewarming is an essential part of hypothermia treatment. The clinician must understand the classes of rewarming methods available, the potential drawbacks of different methods, and the proper rewarming choice based upon core body temperature and the presence or absence of circulation (algorithm 1).

Passive rewarming — Passive rewarming includes removing cold or wet clothing and applying dry insulation such as blankets in a warm environment. Passive rewarming requires the child to generate heat and does not offer patient support. Although passive methods may help prevent further cooling, they should be accompanied by appropriate active rewarming techniques for children in any stage of hypothermia.

Active external rewarming — Active external rewarming techniques heat the body surface. These methods include forced air rewarming (picture 1), radiant heat, and the application of chemical heat packs or plumbed-water heating pads. Our preferred method, forced air rewarming, may lessen the potential for burns of under-perfused skin sometimes seen with heating packs or pads [7,8]; small adult series suggest it may also decrease afterdrop [9-11]. When using heat packs or pads, the trunk is often rewarmed first, if feasible, to avoid mobilizing blood from cold extremities.

Although active external rewarming techniques are simple and widely available, they may have drawbacks such as mobilizing cold and acidemic blood from the extremities into the central circulation and promoting afterdrop (further cooling), hypotension (rewarming shock), ventricular fibrillation (VF), or asystole.

Active external rewarming may be ineffective and possibly harmful in patients with severe hypothermia or absent circulation and should be avoided in such cases unless no other measures are available [12]. (See 'Severe hypothermia with absent circulation' below.)

Active internal rewarming — These techniques all provide heat internally to the patient but take several forms.

●Noninvasive – Noninvasive techniques include the provision of heated, humidified oxygen (temperature 37°C [98.6°F]) and warmed intravenous (IV) normal saline (temperature 40 to 44°C [104 to 111°F]). Although simple to apply, and useful to prevent further cooling, these methods alone do not provide effective rewarming.

●Invasive – Invasive internal rewarming techniques include lavage of the pleura, bladder, stomach, or peritoneum with heated normal saline (temperature 40 to 44°C). These techniques, especially pleural lavage, are suggested for patients with severe hypothermia (core temperature <28°C [82°F]), especially with some preserved circulation, or those with moderate hypothermia and inadequate response to initial rewarming (algorithm 1) [4]. (See 'Severe hypothermia with absent circulation' below.)

●Extracorporeal – Extracorporeal rewarming involves extracorporeal life support (ECLS) methods such as extracorporeal membrane oxygenation (ECMO). ECMO may have advantages in terms of anticoagulation, treatment of pulmonary dysfunction, and ongoing utility even after rewarming. Extracorporeal rewarming is suggested for children with severe hypothermia and absent circulation or in patients for whom other techniques prove ineffective. (See 'Severe hypothermia with absent circulation' below.)

PREHOSPITAL CONSIDERATIONS — 

Clinicians involved in directing the rescue and transport of hypothermic patients must be familiar with an evolving array of prehospital staging systems [13,14]. For summary purposes, we suggest these guidelines:

●Recognition of hypothermia – Suspicion of hypothermia is vital, but, paradoxically, more severe hypothermia may be harder to recognize. Rescuers and medical control clinicians should consider hypothermia not only in children with obvious environmental exposure but also in all children who have altered mental status or who require critical care.

The measurement of core temperature in the field can be difficult or impossible [14]. Critical care decisions should be deferred until the patient arrives at a center equipped to measure accurate core temperatures. Advanced care rescue and transport systems, especially in remote areas, may want to invest in methods such as esophageal or bladder temperature probes.

●Prehospital declaration of death – Clinical findings used in the field to estimate the stage of hypothermia should not guide life-and-death decisions. When in doubt and unable to obtain an accurate temperature, it is better to assume hypothermia, continue resuscitative efforts, and transport the patient to a health care facility [3,5]. (See 'Decision to resuscitate and rewarm' below.)

Because severe hypothermia may permit remarkable survival despite apparent signs of death, even after prolonged cardiac arrest [12,15-17], only very rare cases permit the prehospital declaration of death in children if hypothermia cannot be excluded [3,5,13,14]. These cases include the impossibility of rescue, the presence of clearly lethal injuries (eg, decapitation), or documentation of valid "do not resuscitate" orders.

All the clinical signs usually indicative of death are typical of severe hypothermia, and some signs (eg, flushing) may disguise the presence of hypothermia. In addition, many intact hypothermia survivals have followed delayed rescue, prolonged transport, and prolonged cardiopulmonary resuscitation. (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Clinical presentation'.)

●Patient care and transport – Prehospital providers should avoid patient exertion and rough handling during rescue because these actions may cause mobilization of cold, acidic blood to the heart, promoting cardiac arrhythmias or arrest [18]. Patients should be extracted from the cold environment in a horizontal position, if possible.

Hospital considerations of withholding CPR in selected cases of severe hypothermia are often moot in the field, where assessment of both core temperature and circulation may be difficult. Standard chest compressions should be provided without delay if there is any uncertainty about core temperature or a perfusing rhythm [4,19]. Experts advise rescuers to check carefully for any signs of life for up to one minute [19]. In difficult rescue settings, delayed, intermittent, and prolonged cardiopulmonary resuscitation (CPR) may also be considered [14].

Many hypothermic patients arrive at the hospital colder than they left the scene. Rescue, transport, and treatment involve multiple risks for further cooling. During transport, rescuers should take all possible steps to prevent further heat loss. Key interventions include:

•Removal of wet clothing

•Effective protection with vapor barriers and insulating layers

•Warming of the transport vehicle

•Provision of warm intravenous (IV) fluids, if possible

When mild hypothermia is suspected external warming of the trunk may be helpful, but physicians directing rescue and prehospital services for children must stay current with evolving methods and cautions [14].

In moderate to severe hypothermia, however, external rewarming may increase afterdrop (a continued decline in body temperature) and rewarming shock and may potentiate fatal collapse [14,20-22]. Children may be at increased risk of these ill effects due to decreased body mass and increased peripheral vasoconstriction. Therefore, we withhold active external rewarming during short transports in children with suspected moderate or severe hypothermia. An exception might be longer transports by advanced care teams, a setting where forced-air rewarming may have advantages [14]. (See 'Active external rewarming' above.)

●Interhospital transfer – Children with moderate hypothermia warrant transport to a hospital with pediatric intensive care capability [3,5,23]. Patients with severe hypothermia should ideally undergo consultation with and transport to a hospital that has pediatric ECMO capabilities whenever possible [3,24]. Some transport teams have policies against initiating transfer in patients receiving prolonged CPR; such rules should be waived in patients with severe hypothermia.

HOSPITAL STABILIZATION — 

Successful resuscitation of the hypothermic child requires rapid attention to supportive care (airway, breathing, circulation), assessment and treatment of injury or other medical conditions, and, most of all, effective rewarming interventions.

Rewarming efforts should be guided by the severity of hypothermia and the presence or absence of circulation (algorithm 1); pediatric advanced life support guidelines require important modifications for patients with moderate or severe hypothermia. (See 'Perfusing bradycardic rhythms' below and 'Nonperfusing cardiac rhythms' below.)

Measure core temperature and prevent further cooling — During initial stabilization, the accurate measurement of core body temperature is essential to proper treatment and should occur in conjunction with support of airway, breathing, and circulation. Ideally, children with suspected hypothermia should have their core temperature taken with a low-reading flexible thermometer probe. Rectal temperatures should be taken deep in the rectum but may still show time lags. Preferred central sites include the bladder, esophagus, nasopharynx, or a central vein. In critical cases, we recommend measurement at two or more separate central sites. (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Diagnosis'.)

Hypothermic children should be maintained in a horizontal supine position and handled gently. Clinicians should remove any wet clothing and insulate the victim from further exposure (eg, cover with dry blankets). The following measures should be initiated in all patients until the degree of hypothermia and appropriate type of rewarming is determined (see 'Rewarming' below):

●If circulation is impaired, do not start external rewarming. (See 'Severe hypothermia with absent circulation' below.)

●Give heated, humidified oxygen (37°C [98.6°F]). Respiratory therapy departments will have access to warmed humidifiers.

●Give intravenous (IV) fluid (eg, normal saline) warmed to 40 to 44°C (104 to 111°F); room-temperature (eg, 21°C [70°F]) solutions will cause further cooling and may precipitate ventricular fibrillation (VF) or asystole.

Delivery of warmed IV fluids requires the use of specific trauma-style fluid warmers with short, large-bore, insulated or countercurrent tubing. Standard coil blood warmers will not effectively warm fluid, and standard IV tubing will not keep the fluid warm as it passes to the patient.

Note that these methods alone, although useful to prevent further cooling, may not provide enough heat to achieve rewarming [25,26].

Airway and breathing — Careful, gentle respiratory support is indicated. We suggest these measures:

●Warmed, humidified 100 percent oxygen via a nonrebreather mask for all patients.

●Bag-valve-mask ventilation for hypoventilatory children, or when preparing for endotracheal intubation.

●Endotracheal intubation for patients with airway compromise, respiratory failure, hypotensive shock, or cardiac arrest.

When indicated, endotracheal intubation should not be delayed in the hypothermic child. However, it should be performed in a gentle manner with minimal movement of the patient. Cardiac rhythm should be closely monitored during the procedure [4].

Direct laryngoscopy may be difficult in severe hypothermia because muscular rigidity prevents jaw movement; oral intubation using a videolaryngoscope or other advanced airway techniques may be helpful. (See "The difficult pediatric airway for emergency medicine" and "Video laryngoscopy and other devices for difficult endotracheal intubation in children: Overview and techniques", section on 'Choice of technique'.)

Although VF had been a theoretical concern in patients with moderate or severe hypothermia who undergo endotracheal intubation, a case series of 428 adults with hypothermia found that none of the 97 patients who were endotracheally intubated with core temperatures ≤32.2°C (90°F) developed VF [27].

Circulation — Hypothermia can have profound effects on the cardiovascular system. For reasons discussed below, proper treatment may require modification of Pediatric Advanced Life Support algorithms guided by core temperature, cardiac rhythm, and circulatory status [4].

Vascular access and intravenous fluid therapy — Hypothermia-induced vasoconstriction may make vascular access difficult, especially in children. However, vascular access is vital because aggressive, warmed volume expansion is critical in the treatment of moderate and severe hypothermia. If adequate peripheral IV access (two 22-gauge or larger peripheral IVs) is not rapidly available, the clinician should place an intraosseous needle or central line via the femoral vein. Femoral placement is preferred to central access sites that involve intracardiac placement because catheters are kept out of the potentially irritable myocardium. (See "Emergency and elective venous access in children" and "Intraosseous infusion".)

Treatment of hypovolemia — Patients with moderate or severe hypothermia almost always become disproportionately hypovolemic due to diuresis and fluid shifts. Room-temperature fluids (eg, 21°C [70°F]) worsen all but the most profound hypothermia. Therefore, these patients should initially receive heated (40 to 44°C [104 to 111°F]) IV normal saline using high-capacity warmers and tubing to deliver the first bolus of 20 mL/kg over 5 to 10 minutes; after assessment, a second bolus is given as needed.

Constant reassessments of volume status and rapid provision of additional warmed IV boluses are required, bearing in mind that aggressive and ongoing volume expansion is frequently required in hypothermia. (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Pathophysiology' and "Shock in children in resource-abundant settings: Initial management", section on 'Volume and rate'.)

The adequacy of volume support can be difficult to assess in the moderately or severely hypothermic patient. Measurements of central venous pressure and central venous oxygen saturation may help guide resuscitation. A catheter below the diaphragm is preferred to avoid the risk of arrhythmias from contact with the heart.

An indwelling bladder catheter should be placed to assess urine output; this also aids the recognition and replacement of the excess renal fluid losses or "cold diuresis" common in moderate to severe hypothermia. Bladder catheters with built-in temperature probes also offer a useful means of monitoring core temperature.

Hypotension and bradycardia are common in severe hypothermia and should be treated by effective rewarming alongside aggressive administration of warmed isotonic fluid. Persistent hypotension or bradycardia after rewarming may be further treated using standard measures, including vasopressors or inotropes. (See "Shock in children in resource-abundant settings: Initial management", section on 'Cardiogenic shock' and "Use of vasopressors and inotropes".)

Perfusing bradycardic rhythms — Rewarming is the primary treatment for bradycardic perfusion rhythms in children with hypothermia. Perfusing rhythms associated with hypothermia include sinus bradycardia, first degree atrioventricular block, and atrial fibrillation with slow ventricular response [28]. In severe hypothermia, these rhythms are felt to be adequate for maintaining sufficient oxygen delivery [4]. Thus, bradycardia may be physiologic in severe hypothermia, and cardiac pacing generally is not required unless the bradycardia persists despite rewarming to 32 to 35°C (90 to 95°F). Similarly, medications for bradycardia (eg, atropine, epinephrine) may be withheld in severe hypothermia because the heart rate may revert to normal with rewarming.

Nonperfusing cardiac rhythms — The development of VF, ventricular tachycardia (VT) without a pulse, pulseless electrical activity (PEA), or asystole is common in patients with moderate or severe hypothermia. Aggressive active internal rewarming or, ideally, extracorporeal rewarming may be the primary treatment in these patients because arrhythmia treatment without rewarming is often ineffective [4]. Case reports with intact neurologic survival have sometimes documented the spontaneous conversion of asystole to VF, and of VF to sinus rhythm, with rewarming alone [15,29,30]. (See 'Severe hypothermia with absent circulation' below.)

Decision to resuscitate and rewarm — The presence of hypothermia with a core temperature <32°C (90°F) must alter decisions to withhold or terminate treatment. At these temperatures, decreased metabolism may protect against hypoxia. Recognizing that severe hypothermia may be neuroprotective, clinicians may still wonder if one can tell when resuscitation and rewarming should be withheld. Experts generally support the simple guideline that no one is dead until they are warm and dead, citing as exceptions only obviously lethal injuries such as "decapitation, open head injury with loss of brain matter, truncal transection, or incineration" [13,14].

An ever-growing body of reports and case series document many intact survivals from severe hypothermia despite clinical signs that would signify death at normal temperatures [31-35]. In fact, features of death such as fixed and dilated pupils, pulselessness, apnea, apparent rigidity, dependent lividity, cyanosis, pallor, and palpable cold are typical in severe hypothermia; such markers have been present in many hypothermia victims who underwent successful resuscitation.

Likewise, no core body temperature is too low to resuscitate [14], and almost no duration of arrest is too long. Hypothermic patients without circulation have made intact recoveries from core temperatures as low as 14°C (57°F), after submersions of 66 and 83 minutes, after hours of arrest without CPR, after CPR for as long as six and a half hours, and after total resuscitation time up to nine hours [1,3,15-17,29,36-41].

Clinicians may be concerned about producing hypothermia survivors who are neurologically devastated. In fact, however, evidence suggests that severely impaired survival is uncommon. In a series of 46 adults with severe hypothermia (core temperature <28°C [82°F]) and cardiac arrest, 32 patients were selected for rewarming by extracorporeal methods. Fifteen of these patients had long-term survival, and none had serious long-term neurologic complications [31].

Our experience and many case reports suggest that hypothermia continues to be missed and appropriate resuscitation continues to be withheld. A host of factors can lead to the erroneous declaration of death especially in patients with severe hypothermia (core temperature <28°C [82°F]).

For example, although prolonged submersion in warmer water is associated with anoxic injury [24,41,42], prolonged submersion in very cold water (temperature <10°C [50°F]) may offer anoxic protection. At patient presentation, though, factors such as water temperature, the duration of exposure, and the actual anoxic time are often unclear or even misleading. What is the water temperature in a springtime pond or unused swimming pool? When did immersion become submersion? In a striking case, seven teens whose boat capsized in 2°C (36°F) water were found upon rescue 108 to 169 minutes later apparently lifeless, unconscious and pulseless, with their heads submerged in the water. All seven survived hours of rescue, cardiopulmonary resuscitation, and extra-corporeal rewarming; six of seven made a good neurologic recovery [43].

An even more insidious scenario is hypothermia in so-called bathtub drowning; a bathtub may at first suggest warm water submersion. In fact, though, hypothermia in innocent bathtub drowning is highly suspicious; post-mortem hypothermia develops only slowly, and cases of child abuse in cold water are often misrepresented as bathtub drownings [44,45]. True submersion may be absent in this scenario, and severe cooling may well precede anoxia; thus a reasonable chance of intact survival may exist. In any "bathtub drowning," clinicians should maintain an index of suspicion, measure core body temperature, and in the presence of hypothermia, initiate appropriate resuscitation and rewarming.

Chest compressions — In patients known to be severely hypothermic (core temperature <28°C [82°F]) with very slow or minimally perfusing cardiac rhythms, the risk of myocardial irritability and the potential for return of circulation with rewarming alone lead some experts to suggest that chest compressions be withheld unless a nonperfusing cardiac rhythm (eg, asystole, VF, PEA) is present. Asystole and VF will be evident on a cardiac monitor, but PEA is difficult to confirm in severe hypothermia. Careful palpation for any pulse should be continued up to one minute. Rapid bedside cardiac ultrasound may assist in differentiating PEA from weak cardiac contractions [4].

If, however, there is any uncertainty about either core temperature or a perfusing rhythm, chest compressions should be provided without delay [4,19], and all patients known to have nonperfusing rhythms should receive chest compressions. Chest compressions will be difficult due to muscular rigidity, but modern practice discourages open cardiac massage because the myocardium will also be rigid and the closed-chest mechanics of CPR will be lost. (See "Pediatric basic life support (BLS) for health care providers", section on 'Chest compressions'.)

Ventricular arrhythmias with hypothermia — Patients with hypothermia and VF or VT without a pulse may be refractory to conventional therapy until the patient has been rewarmed [4]. These patients may receive initial defibrillation and pharmacologic therapy as indicated by Pediatric Advanced Life Support guidelines (algorithm 2), but if initial attempts are unsuccessful, CPR and aggressive rewarming must be promptly initiated. Refractory VF has been reported in many cases of severe hypothermia, and spontaneous conversion of VF has been observed with rewarming alone. (See 'Severe hypothermia with absent circulation' below.)

Asystole or pulseless electrical activity — Patients with asystole or PEA and severe hypothermia (core temperature <28°C [82°F]) should receive airway support (endotracheal intubation), chest compressions, and epinephrine per pediatric advanced life support guidelines for cardiac arrest (algorithm 2). They should undergo active internal rewarming, preferably with ECMO [19].

Although the efficacy of epinephrine is decreased in patients with severe hypothermia, limited evidence from animal models suggests that return of spontaneous circulation is promoted when epinephrine is used according to pediatric advanced life support guidelines for cardiac arrest (algorithm 2) in conjunction with aggressive rewarming [4]. Excessive doses should be avoided.

IV dextrose (eg, 0.5 g/kg) should be administered in patients with asystole or PEA for documented or suspected hypoglycemia regardless of core body temperature. (See "Primary drugs in pediatric resuscitation", section on 'Dextrose (glucose)'.)

Children with asystole or PEA and moderate hypothermia (core temperature 28 to 32°C [82 to 90°F]) should receive medications according to established Pediatric Advanced Life Support protocols [4]. Some clinicians may choose to increase the spacing between doses until core temperature is >32°C (90°F). Clinicians should balance the risks and benefits of each medication while recognizing that rapid restoration of circulation is increasingly important as cerebral protection is reduced in this range.

Duration of resuscitation — Resuscitative efforts should continue until the child's core temperature is 34 to 35°C (93 to 95°F). Because of the neuroprotective effects of hypothermia, complete recovery of patients with severe hypothermia and cardiac arrest has been well documented even after extremely prolonged resuscitation [4,12,15,16,29,31,37,40,43,46,47]. Although little neuroprotection occurs above 32°C (90°F), ethical and legal factors suggest that rewarming and resuscitation be continued until the core temperature is approximately 34 to 35°C (93 to 95°F) or until there is return of spontaneous circulation.

Standard prognostic rules change in severe hypothermia. For instance, recommendations about the duration of submersion compatible with survival do not apply in very cold water [42]. Children have survived up to 66 to 83 minutes of submersion in such water [15,17]. Similarly, avalanche victims have survived prolonged burial despite asystole upon extrication [36,48].

A review of cases where survival from near-drowning and hypothermic arrest occurred found that the water temperature was usually <5°C (41°F) and almost always <10°C (50°F) [49]. Water temperature is seldom known with any certainty, though, so resuscitation and rewarming should be provided if any doubt exists. In our experience, the best approach is to rewarm and support the patient and then let the course declare itself.

Caution is required in any attempt to use chemical markers of death. Experts warn that clinical decisions should not rely on just one biological indicator [50]. Although extreme acidosis, hyperkalemia, hyperammonemia, and evidence of intravascular thrombosis (fibrinogen <50 mg/dL) are seen in patients who do not survive hypothermia [51,52], absolutely safe cutoff values have not been defined. Acidosis may be severe; case reports document intact survival in patients with a serum pH as low as 6.51 [53] or 6.29 [32].

When serum potassium is measured in hypothermia, a sample from a central venous source is least likely to show artifactual elevation [50]. Noting that survival has not been documented in a patient with a serum potassium level >12 mmol/L [3], a number of adult guidelines [3,5,37,50] suggest that termination of CPR might be "considered" if a serum potassium measures above that level. However, given that case reports in children document intact survivals with serum potassium levels as high as 11.3 and 11.8 mmol/L [17,54], we do not feel a cutoff value of 12 mmol/L is necessarily safe in pediatric care, and we avoid guidelines that terminate resuscitation for a specific value.

Most experts believe that the neuroprotective effect of hypothermia is lost at core temperatures above 32°C (90°F). In patients with a core temperature between 32 and 34°C (90 and 93°F), rewarming is probably indicated, but the clinician must use judgment as to the duration of resuscitation. Once the core temperature is above 34 to 35°C (93 to 95°F), resuscitation may be stopped following standard Pediatric Advanced Life Support guidelines in patients who have not regained spontaneous circulation despite appropriate interventions.

Glucose homeostasis — Hypoglycemia is common in hypothermia and requires treatment. For patients with documented hypoglycemia or persistent altered mental status and inability to measure a blood glucose, IV dextrose (eg, 0.5 g/kg) should be administered. (See "Primary drugs in pediatric resuscitation", section on 'Dextrose (glucose)'.)

Hyperglycemia is also seen in hypothermia, but by contrast, it should not be treated with insulin, because this will not be effective in the cold patient and may later cause hypoglycemia in the rewarmed child.

REWARMING — 

Clinicians should match the method of rewarming to the degree of hypothermia as well as the presence or absence of circulation (algorithm 1). The classification of rewarming techniques is discussed above. (See 'Rewarming classification and definitions' above.)

Mild hypothermia (core temperature 32 to 35°C [90 to 95°F]) — Patients with environmental exposure and mild hypothermia should undergo removal of wet clothing and drying of skin followed by active external rewarming (eg, forced air heating blanket, radiant heat lamp, or plumbed-water heating pad) [3,25,38]. Administration of warmed intravenous (IV) normal saline or, for patients who are alert and stable, drinking warm liquids also helps prevent further cooling. (See 'Vascular access and intravenous fluid therapy' above.)

Ongoing monitoring of core temperature and continuous monitoring of cardiac rhythm and circulatory status are essential to ensure that these patients respond appropriately to rewarming (algorithm 1). Even children with mild hypothermia may undergo marked afterdrop (further cooling of core body temperature) [38].

If environmental exposure is not a factor in mild hypothermia, other conditions (eg, sepsis, hypoglycemia, hyponatremia, or child abuse (table 2)) must be considered. These children may display symptoms inconsistent with mild hypothermia alone (eg, lethargy, hypotension). Diagnostic testing and appropriate treatment should be instituted as soon as possible. Effective rewarming will be aided by treatment of the underlying cause. (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Differential diagnosis'.)

Moderate hypothermia (core temperature 28 to 32°C [82 to 90°F]) — In addition to warmed humidified oxygen and heated IV normal saline, we suggest that children with intact circulation and moderate hypothermia receive active external rewarming, preferably forced air rewarming (picture 1 and algorithm 1). Although no studies have been performed in children, adults with moderate hypothermia have been shown to respond well to forced air external rewarming. (See "Accidental hypothermia in adults: Management", section on 'Active external rewarming'.)

However, active external rewarming may potentiate both peripheral vasodilation and rewarming shock; the return of cold, acidemic blood to the core circulation causes a drop in temperature and pH. In combination, these effects promote hypotension, decreased coronary perfusion, and ventricular fibrillation, and fatal collapse. Thus, children with moderate hypothermia should have IV access and a rapid infusion of 20 mL/kg of warmed normal saline at the start of rewarming, ongoing volume support guided by continuous cardiorespiratory monitoring, and frequent assessment of blood pressure and perfusion. (See 'Vascular access and intravenous fluid therapy' above.)

Inadequate rewarming rates (temperature rise <1°C [1.8°F] per hour) or a continued drop in core body temperature despite active external rewarming suggest evaluation for inadequate fluid resuscitation and other complications or causes of hypothermia. These patients and those who become unstable are candidates for active internal rewarming methods. (See 'Severe hypothermia with intact circulation' below.)

To avoid induced hyperthermia, many clinicians stop external rewarming when the core temperature reaches 35°C (95°F). Ongoing close temperature monitoring and control are required to prevent re-cooling or hyperthermia during recovery.

Severe hypothermia with intact circulation — Little evidence exists to guide the rewarming of children with severe hypothermia and intact circulation, but adult experience suggests a logical approach. When it is available, we suggest active internal rewarming; if, however, active internal rewarming will be delayed, or if large volumes of heated fluid are unavailable, heated forced air rewarming alone may be attempted. [3,9-11].

Our preferred methods are as follows (algorithm 1):

●Active internal rewarming – We suggest that children with severe hypothermia (core temperature <28°C [82°F]) but preserved circulation be warmed by active internal methods when these are available. These methods include heated saline lavage of the pleural space, bladder, stomach, and/or peritoneum. When compared with external rewarming, this approach may be more likely to avoid significant core temperature afterdrop, shock, and/or cardiac arrhythmias.

Our preferred active internal rewarming method is left pleural lavage with heated normal saline [55-60]. This procedure is performed by placing two chest tubes in the left pleural cavity that are positioned so that inflow is anterior and drainage is posterior. Fluid heated to 40 to 44°C (104 to 111°F) is instilled through the anterior chest tube and warms the heart directly. Some clinicians have chosen right pleural lavage because it avoids the theoretical risk of the left ventricle being struck by the chest tube during insertion and causing VF. Right pleural lavage may, however, be slightly less effective because it bathes a smaller area of the heart.

Heated normal saline lavage of the stomach, bladder, colon, and peritoneum are generally less effective than pleural lavage, but all have been used successfully in some cases. Though it may risk pulmonary aspiration, gastric lavage is the easiest and most familiar, and it provides centralized warming close to the heart. The optimal dwell time during lavage is unknown. Our approach is to use a dwell time of 10 to 15 minutes to permit adequate heat transfer without excessive cooling of the lavage fluid [61].

The need to rapidly provide large quantities of heated saline presents a practical challenge in all the lavage techniques. Preplanning may suggest solutions such as using trauma-suite IV warmers or peritoneal-dialysis heating tubs. In one case, successful resuscitation was achieved with pleural lavage using 75 L of heated tap water when adequate amounts of normal saline were not available [30]. Use of an autotransfusion setup is an alternative method to permit large volume lavage with limited fluid supplies [61].

●Forced air external rewarming – As noted, we prefer active internal rewarming when it is feasible, but would resort to forced air rewarming if it were not. In a small trial and two case series reporting forced air rewarming in 28 adults with core temperatures ranging from 24 to 34°C (75 to 93°F), all the patients with intact circulation (n = 22) had complete recovery [9-11]. No patients developed afterdrop or rewarming shock. The mean core rewarming rate was 1.0 to 2.4°C (1.8 to 4.0°F) per hour; the maximum achieved was 3.4°C (6.0°F) per hour.

Severe hypothermia with absent circulation — If possible, we suggest that children with severe hypothermia (core temperature <28°C [82°F]) and absent circulation undergo rapid rewarming with extracorporeal methods such as ECMO.

Advantages of ECMO include circulatory support, oxygenation with hemodilution, anticoagulation, treatment of pulmonary dysfunction, and potential ongoing benefit after rewarming [3,40]. Equally important, this method provides rapid rewarming, even in cardiac arrest. Extracorporeal methods can achieve rewarming rates up to 10°C (18°F) per hour. This method has been widely used in reported cases of intact neurologic survival from hypothermic cardiac arrest [17,31,33,62] and in children as young as two years of age [15,23].

Because requirements include large-bore arterial and venous cannulation as well as specialized equipment and personnel, a preplanned team approach is ideal [23]. Transfer to a center with ECMO capabilities has been suggested for any patient with hypothermia and cardiac instability or cardiac arrest [3]. Transfer for ECMO even after rewarming has been helpful for patients needing continued circulatory and respiratory support [63].

Furthermore, delays have not prevented success. Patient transport for up to three hours and CPR for up to six hours prior to institution of ECMO and ECLS have still been associated with good outcomes [64]. Their primary contraindication, severe associated trauma with risk of bleeding due to heparin, may be addressed by using non-heparinized bypass circuits [65].

Alternative methods for severe hypothermia — When extracorporeal techniques are unavailable or markedly delayed, other approaches may succeed and should be attempted, including:

●Active internal rewarming with CPR – Heated left-pleural lavage, as described above, and at times other internal rewarming methods, have been used successfully in cardiac arrest [18,66] when extracorporeal rewarming is unavailable or contraindicated [56]. Some clinicians suggest bilateral pleural lavage in these patients, especially in those children who are initially unresponsive to left-pleural lavage alone.

●Combined methods of active external rewarming with CPR – Although impaired circulation limits the effectiveness and increases the hazards of external rewarming, case reports in several children [12,60] emphasize that when extracorporeal methods are unavailable, a combination of other methods may be effective. Forced air rewarming has at times been used in these combined efforts and may be especially advantageous.

●Other extracorporeal methods – Successful core rewarming with intact survival has been described using hemodialysis and hemofiltration systems as well as arteriovenous [18] and venovenous shunts [66]. However, these methods have much slower rewarming rates than ECMO methods (2 to 3°C [3.6 to 5.4°F] per hour versus 9.8°C [17.6°F] per hour). In addition, such methods are not widely available and may be difficult to perform in infants and young children. When these methods are used, prolonged CPR up to and beyond four hours may be required but may still produce intact recovery [16].

●Endovascular warming – Endovascular temperature-control catheters placed in a central vein (eg, inferior vena cava), with warmed fluid pumped through a closed-loop system in the tip, can directly heat blood in the central circulation. Although successful warming has been reported with such catheters [67], an adult case series failed to demonstrate a significant difference in rewarming rates when endovascular warming was added or compared to standard active internal rewarming [68]. Further study appears warranted before this method is suggested for children.

Rewarming rates — At one time, specific, sometimes slower, rewarming rates were targeted, but all evidence suggests that actual rewarming rates are determined by the patient's circulation and metabolism more than by the clinician. What's more, rapid rewarming is not harmful if sufficient support is provided for blood volume and circulation. In fact, evidence suggests that rapid rewarming is associated with lower mortality after adjusting for case severity [69], and case reports identify large numbers of patients with intact survival after profound hypothermia (core temperature <25°C [77°F]) rewarmed very rapidly using extracorporeal circulation [31-34].

In practical terms, rewarming rates <1°C per hour lead to very long resuscitations and are an indication to enhance rewarming (eg, to move on from active external to active internal rewarming) [39].

Failure to rewarm — More aggressive rewarming techniques are indicated if patients fail to rewarm. Reversible factors such as hypoglycemia or hyponatremia should be identified and treated.

Failure to rewarm in the presence of possible infection may suggest treatment with appropriate antibiotics. Some experts have also suggested that all patients who fail to increase their core body temperature at a rate greater than 0.6°C per hour (1°F per hour) despite appropriate rewarming efforts warrant administration of empiric broad-spectrum IV antibiotics. (See "Children with sepsis in resource-abundant settings: Rapid recognition and initial resuscitation (first hour)", section on 'Empiric antibiotic therapy'.)

The clinician should also evaluate for other potential causes of hypothermia such as adrenal insufficiency, toxins, brain injury due to trauma or child abuse, and other central nervous system dysfunction (table 2). (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Differential diagnosis'.)

If adrenal failure is considered, empiric treatment with IV hydrocortisone based on age (eg, <3 years, 25 mg; 3 to 12 years, 50 mg; 12 years and older, 100 mg) may be warranted. If possible, the clinician should obtain blood for adrenocorticotropic hormone (ACTH) and serum cortisol measurement prior to steroid treatment. (See "Treatment of adrenal insufficiency in children".)

FROSTBITE — 

Frostbite frequently accompanies hypothermia caused by environmental exposure to cold. Clinical manifestations, diagnosis, and treatment of frostbite and other cold injuries are discussed separately. (See "Frostbite: Acute care and prevention".)

POST-RESUSCITATION CARE — 

Post-resuscitation care is guided by the degree of hypothermia and patient stability:

●Unstable patients and those resuscitated from moderate or severe hypothermia warrant ongoing care in a pediatric intensive care unit. Key aspects of care include:

•Ongoing support of airway, breathing, and circulation as well as treatment of possible pulmonary edema or cardiovascular instability. Extracorporeal membrane oxygenation (ECMO), for example, has at times been used for days in such patients [3,24,63].

•Continuous cardiorespiratory and core temperature monitoring with frequent blood pressure measurement.

•Repeated measurement of serum electrolytes, blood urea nitrogen, and serum creatinine to assess for electrolyte abnormalities and renal dysfunction.

•Repeated measurement of prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR) to identify hypothermia-induced coagulopathy.

Pulmonary edema, coagulopathy, and renal failure may resolve within days. Neurologic abnormalities, however, sometimes persist for weeks to months even in cases where they eventually resolve. (See 'Prognostic decision making' below.)

If initial resuscitation takes place in a facility without pediatric intensive care resources, the patient should be stabilized and transported to a facility with a pediatric intensive care unit and, whenever available, an ECMO team. The prior establishment of hypothermia management protocols and transfer agreements at both referring hospitals and receiving regional pediatric centers is strongly encouraged.

●Children with mild environmental hypothermia who appear recovered and stable after rewarming may be discharged to reliable caretakers. In children with other causes, management decisions are guided by the underlying medical condition (table 2). (See "Hypothermia in children: Clinical manifestations and diagnosis", section on 'Differential diagnosis'.)

Prognostic decision making — Decisions about continued life support and neurologic prognosis during the post-rewarming period should be extended beyond the timeframe used in standard care. Intact recovery has been described after prolonged intensive support (eg, up to five days of ECMO) [63]. Repeated neurologic evaluations including Glasgow Coma Scale and other prognostic tools have suggested a poor prognosis, sometimes for many days, in hypothermic patients who later make an intact recovery [17,70]. Surviving patients with neurologic deficits also warrant aggressive rehabilitation; case reports indicate that full neurologic recovery may not be complete for months [15,29].

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Hypothermia".)

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Hypothermia (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition – Hypothermia is defined as a core body temperature below 35°C (95°F). The stage of hypothermia, defined by core temperature, has a major impact on both recognition and treatment. The most commonly used definitions are as follows (see 'Definition of hypothermia' above):

•Mild – Core temperature 32 to 35°C (90 to 95°F)

•Moderate – Core temperature 28 to 32°C (82 to 90°F)

•Severe – Core temperature below 28°C (82°F)

The degree of hypothermia may be initially estimated from clinical findings (table 1), but such estimates are imprecise. Core body temperature, not clinical findings, must guide the management of hypothermia.

●Core temperature measurement – Children with suspected hypothermia should have their core temperature measured and monitored, if possible, with a low-reading flexible thermometer probe at a central site (eg, bladder, deep rectum, distal esophagus, nasopharynx, or a central vein). Failing this, a deep rectal temperature may be used but will be subject to artifact and time lags. In unstable patients, we recommend measurement at two or more separate central sites. (See 'Measure core temperature and prevent further cooling' above.)

●Prevent further cooling – To prevent further cooling (see 'Measure core temperature and prevent further cooling' above):

•Maintain hypothermic children in a horizontal supine position and handle them gently.

•If not already done by prehospital personnel, remove wet clothing and insulate the victim from further exposure (eg, cover with dry blankets).

•Give the patient warmed, humidified 100 percent oxygen and heat any administered intravenous (IV) fluids to 40 to 44°C (104 to 111°F).

•Avoid application of external heat in patients with impaired circulation.

●Airway and breathing – Gently perform endotracheal intubation with minimal movement for patients with airway compromise, respiratory failure, hypotensive shock, or cardiac arrest. Direct laryngoscopy may be difficult because of rigidity of the jaw muscles and requires advanced airway techniques. (See "The difficult pediatric airway for emergency medicine" and "Video laryngoscopy and other devices for difficult endotracheal intubation in children: Overview and techniques", section on 'Choice of technique'.)

●Circulation – Patients with moderate or severe hypothermia warrant aggressive fluid resuscitation consisting of 20 mL/kg of heated (40 to 44°C [104 to 111°F]) IV normal saline using high-capacity warmers and tubing to deliver the first bolus over 5 to 10 minutes and repeated as needed based upon the patient's hemodynamic status. IV fluids should be started at the same time as rewarming. (See 'Vascular access and intravenous fluid therapy' above.)

●Pediatric advanced life support (PALS) – Treatment of cardiac arrhythmias and cardiac arrest may require modification of PALS algorithms as follows:

•Perfusing bradyarrhythmias – Rewarming is the primary treatment for bradycardic perfusion rhythms in children with severe hypothermia. Cardiac pacing is typically ineffective and is not employed in children with severe hypothermia; perfusing slow cardiac rhythms are felt to be adequate. (See 'Perfusing bradycardic rhythms' above.)

•Cardiac arrest – The presence of hypothermia with a core temperature <32°C (90°F) alters typical decisions to withhold or terminate treatment. In such patients, prognostic features that suggest nonviability in normothermia are notoriously misleading. Unless clearly lethal injuries are present, CPR should be provided at once. (See 'Nonperfusing cardiac rhythms' above and 'Decision to resuscitate and rewarm' above.)

If indicated, patients with severe hypothermia (core temperature <28°C [82°F]) and cardiac arrest should receive initial defibrillation or pharmacologic therapy as indicated by Pediatric Advanced Life Support guidelines (algorithm 2). Prompt initiation of active internal rewarming (ideally extracorporeal membrane oxygenation) is also essential. (See 'Chest compressions' above and 'Ventricular arrhythmias with hypothermia' above and 'Asystole or pulseless electrical activity' above.)

•Duration of resuscitation – Because of the neuroprotective effects of hypothermia, complete recovery of patients with hypothermia and cardiac arrest has been well documented despite prolonged resuscitation. Thus, resuscitative efforts with rewarming should continue at length (if need be, for hours) until the core temperature is approximately 34 to 35°C (93 to 95°F) or there is a return of spontaneous circulation. (See 'Duration of resuscitation' above and 'Decision to resuscitate and rewarm' above.)

●Rewarming – Simultaneously with stabilization of airway, breathing, and circulation, clinicians should provide rewarming as determined by the degree of hypothermia and the presence or absence of circulation (algorithm 1):

•Mild hypothermia – Patients with mild hypothermia (core temperature 32 to 35°C [90 to 95°F]) should undergo removal of wet clothing and drying of skin followed by active external rewarming. (See 'Mild hypothermia (core temperature 32 to 35°C [90 to 95°F])' above.)

•Moderate hypothermia – For children with intact circulation and moderate hypothermia (core temperature 28 to 32°C [82 to 90°F]), we suggest active external rewarming, preferably by forced air methods (picture 1) (Grade 2C). When using other external methods, the trunk may be rewarmed first to avoid mobilizing blood from cold extremities. (See 'Moderate hypothermia (core temperature 28 to 32°C [82 to 90°F])' above.)

•Severe hypothermia with intact circulation – For children with severe hypothermia (core temperature <28°C [82°F]) but preserved circulation, we suggest active internal methods (Grade 2C). These methods include heated saline lavage, especially of the left pleural space, or possibly the bladder, stomach, or peritoneum. Forced air rewarming may be useful if active internal rewarming methods are delayed or large volumes of heated fluid are unavailable. (See 'Severe hypothermia with intact circulation' above.)

•Severe hypothermia with absent circulation – For children with severe hypothermia (core temperature <28°C [82°F]) and absent circulation, we suggest extracorporeal methods, preferably extracorporeal membrane oxygenation [ECMO]) whenever available (Grade 2C). If such methods are not available, the best alternative is aggressive active internal rewarming. (See 'Severe hypothermia with absent circulation' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges Robert Bolte, MD, who contributed to earlier versions of this topic review.