Hypothermia in children: Clinical manifestations and diagnosis

INTRODUCTION — This article reviews the clinical manifestations, diagnosis, and differential diagnosis of hypothermia in children.

Treatment of hypothermia in children, neonatal hypothermia, and frostbite are discussed separately. (See "Hypothermia in children: Management" and "Overview of short-term complications in preterm infants", section on 'Hypothermia' and "Frostbite: Emergency care and prevention".)

DEFINITION OF HYPOTHERMIA — Hypothermia is defined as a core body temperature below 35°C (95°F). The stage of hypothermia, as defined by core temperature, is important in both recognition and treatment. Three stages may be defined as follows [1-3]:

●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)

A core temperature <25°C (77°F) is sometimes defined as profound hypothermia [2].

Published temperature cutoffs vary slightly [3], but all cutoffs are approximate because of imprecise measurement and individual patient variation.

Core body temperature should be measured as soon as possible. Although clinical staging schemes have been proposed for prehospital and rescue settings, experts emphasize that core temperature measurement is critical for diagnosis and treatment [2,4,5]. (See "Hypothermia in children: Management", section on 'Prehospital considerations'.)

EPIDEMIOLOGY — In the United States, approximately 1000 to 1300 deaths from primary hypothermia are reported annually [6]. Estimated death rates among infants and children younger than 14 years of age range from 0.2 to 1 death per million, although the diagnosis may be missed in a significant number of deaths. (See 'Pathophysiology' below.)

Missed hypothermia is common, and the consequences may be fatal. Although generally harmful, severe hypothermia may provide cerebral protection against anoxia. For more than 30 years, many centers have published remarkable series of survival even after prolonged arrest [3,7-12]. Intact survival rates in these series range from 22 to 60 percent or more [11-13]. Thus, the recognition of hypothermia is not just critical to management but may be lifesaving.

PATHOPHYSIOLOGY — Heat is lost from the body by radiation, conduction, convection, evaporation, and respiration [14]. Radiation can account for up to 50 percent of heat loss, even indoors [15]. Convection may account for 25 percent of heat loss in still air, and much more in wind. Wet clothing increases evaporation; in severe conditions, this heat loss may be six times basal metabolic heat production. Conduction, although low in air, is approximately 25 times more rapid in water. Finally, cooling during rescue and resuscitation will be hastened by continued exposure, respiratory heat loss, or the infusion of room-temperature fluids.

The stages of hypothermia correspond to the physiologic responses to cold (table 1) [1,2,14]. During mild hypothermia (core temperature 32 to 35°C [90 to 95°F]), the body increases heat production by shivering and increasing metabolism and decreases heat loss by peripheral vasoconstriction.

In moderate hypothermia (core temperature 28 to 32°C [82 to 90°F]), compensatory mechanisms begin to fail; cardiorespiratory depression and altered mentation may develop.

In severe hypothermia (core temperature <28°C [82°F]), the basal metabolic rate drops to approximately half of normal. Body systems including circulation, ventilation, and mentation become markedly depressed or cease to function. As the core temperature falls further, coma, fixed and dilated pupils, apnea, and pulselessness develop, and muscles become rigid due to dysfunction of actin-myosin bundles.

This virtual shutdown of metabolism, though, may also provide protection against prolonged anoxia. Many very cold patients with the clinical appearance of death have made intact recoveries even after resuscitation that is markedly delayed and prolonged. Failure to recognize and treat such patients constitutes a fatal missed diagnosis (See "Hypothermia in children: Management", section on 'Duration of resuscitation'.)

Key pathophysiologic changes in hypothermia include [2,16]:

●Respiratory depression – Respiration progressively becomes slow, shallow, irregular, and then absent.

●Hypovolemia – Blood volume markedly decreases because of extravasation due to vascular leak and a profound "cold diuresis" caused by erroneous internal sensing of blood volume as well as failure of renal concentrating function. The hydrostatic effects of immersion further promote hypovolemia in water rescue [17].

●Circulatory collapse – Cardiac output is reduced by hypovolemia, sludging of blood due to cold, decreased myocardial contractility, and bradycardia. In addition, the loss of vasomotor regulation drops systemic vascular resistance. These combined effects lead to circulatory collapse.

●Arrhythmias – Hypothermia increases myocardial irritability. Ventricular fibrillation (VF) is a frequent problem in severe hypothermia [18]. Potential triggers of VF include rough patient handling, patient exertion, core temperature afterdrop (further cooling of the body after being removed from cold exposure), administration of room-temperature fluids, direct stimulation of the myocardium (eg, intracardiac central lines), and rewarming shock. (See "Hypothermia in children: Management", section on 'Measure core temperature and prevent further cooling' and "Hypothermia in children: Management", section on 'Active external rewarming'.)

●Other – Variable effects of hypothermia may include hypo- or hyperglycemia, hyperkalemia, metabolic acidosis or alkalosis, thrombocytopenia, and coagulopathy [14].

Pediatric considerations — Children, especially young children and infants, are at greater risk for hypothermia than adults for several reasons [14,19]:

●The younger the child, the larger the ratio of body surface area to mass.

●Young infants do not have the ability to increase heat production through shivering.

●Infants and young children have limited glycogen stores to support heat production.

●Children may have decreased ability to recognize, avoid, or escape hypothermic exposure.

●Children with predisposing conditions (eg, endocrine malfunction) or insults such as trauma, burns, or drug overdose are at particular risk. (See 'Differential diagnosis' below.)

●The history may not suggest hypothermia. Pediatric hypothermia does not require extreme exposure. Furthermore, child punishment and abuse with cold water has been reported but is often omitted from caregiver histories [20-23].

Relative to adults, young children may have better clinical outcomes and better preservation of neurologic function after significant hypothermia. The neuroprotective effect of hypothermia depends on a combination of rapid cooling and preserved circulation, both more common in children. (See "Hypothermia in children: Management", section on 'Decision to resuscitate and rewarm'.)

CLINICAL PRESENTATION — Hypothermia should be suspected in any child with a history of prolonged exposure to a cold environment but may also occur with severe illness or injury, transport and resuscitation, child abuse, or toxic exposure.

Common scenarios for exposure include:

●Runaway or lost children

●Cold-water near-drowning and immersion victims

●Winter and mountain accident victims

●Intoxicated adolescents who become incapacitated outdoors

The stage of hypothermia may be estimated from clinical features (table 2), but the features and onset vary from patient to patient [14], especially mental status changes and possible cardiac arrhythmias. Thus, a precise measurement of core body temperature is needed to confirm the diagnosis and guide treatment. (See 'Diagnosis' below.)

Further cooling or rough handling should be prevented during assessment to avoid promotion of shock or ventricular fibrillation (VF) in the moderately to severely hypothermic patient [2].

Because the diagnosis is frequently overlooked, clinicians must maintain a high index of suspicion for hypothermia. The obvious signs of chilling, such as acrocyanosis and shivering, are features of mild hypothermia, while severe hypothermia paradoxically obscures or even reverses these signs.

Subject to some variation and overlap, the clinical features of hypothermia by stage are typically as follows [2,16]:

●Mild hypothermia – Between approximately 32 and 35°C (90 to 95°F), the child may display shivering, piloerection ("goose bumps"), and peripheral vasoconstriction with prolonged capillary refill time, pallor, and acrocyanosis. These changes arise from physiologic mechanisms designed to preserve core body temperature.

Of note, young infants try to preserve heat by intense peripheral vasoconstriction, have limited ability to shiver, and are less able to maintain body heat than older children. Cold infants may display "paradoxical rosy cheeks" and a healthy appearance.

●Moderate hypothermia – Mental function typically decreases between 28 and 32°C (82 to 90°F). Shivering stops, and the patient displays slurred speech, clumsy movements, and impaired thinking. In general, agitation and distress give way to confusion, lethargy, and irrational behavior such as "paradoxical undressing" as core body temperature continues to drop. Children with paradoxical undressing have been initially misdiagnosed as sexual assault victims [16].

As hypothermia progresses, shivering stops and heart rate, ventilation, and blood pressure become variable and depressed.

●Severe hypothermia – In severe hypothermia, bradycardia and hypotension progress to pulselessness, VF, or asystole. Although VF or asystole are typical endpoint rhythms in hypothermia, a number of other rhythms may occur including sinus bradycardia, atrioventricular block, atrial fibrillation, and junctional rhythm. (See 'Electrocardiogram' below.)

Stupor gives way to unresponsive coma with fixed and dilated pupils.

Below approximately 28°C (82°F), the appearance of hypothermia becomes less obvious because of muscle rigidity and flushed skin. Patients with such muscle rigidity are often described as "frozen stiff." However, freezing does not occur above a core temperature of 0°C (32°F); this rigidity is due to dysfunction of actin-myosin bundles. Unfortunately, such features as apparent rigor mortis, skin flushing, absent shivering, and absent vital signs may lead to the missed diagnosis of hypothermia and a premature declaration of death in patients who might have made a viable recovery.

ANCILLARY STUDIES

Laboratory studies — The impact of hypothermia on laboratory evaluation is discussed in more detail separately. (See "Accidental hypothermia in adults", section on 'Laboratory studies and monitoring' and "Arterial blood gases", section on 'Transport and analysis'.)

Mild hypothermia — Healthy children with acute mild hypothermia who rapidly recover after very brief environmental exposure may not require laboratory testing.

Unexplained, prolonged, moderate, or severe hypothermia — In patients with unexplained, prolonged, moderate, or severe hypothermia, the following studies should be obtained:

●Rapid serum glucose

●Serum electrolytes

●Serum blood urea nitrogen and creatinine

●Lipase

●Complete blood count

●Prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR)

●Blood type and crossmatch studies (if the need for extracorporeal warming is anticipated)

●Arterial blood gas (uncorrected for temperature)

Capillary blood gas samples may be misleading in children with hypothermia because the peripheral circulation is poor. Central venous blood gas measurements may be an appropriate proxy for arterial pH and pCO₂ measurements.

Additional studies may be indicated depending upon clinical circumstances as follows (see 'Differential diagnosis' below):

●Trauma – In children with multisystem trauma or possible child abuse, urine rapid dipstick for blood, urinalysis, liver enzymes (aspartate transaminase [AST], alanine transaminase [ALT]), and blood for typing and cross match may be indicated. (See "Trauma management: Approach to the unstable child", section on 'Laboratory studies' and "Physical child abuse: Diagnostic evaluation and management", section on 'Laboratory studies'.)

●Toxins – Urinalysis, serum osmolality, ethanol level, and urine screen for drugs of abuse (especially benzodiazepines, opioids, and barbiturates) should be performed in children and adolescents with unexplained hypothermia. (See "Approach to the child with occult toxic exposure", section on 'Ancillary studies'.)

●Sepsis – In ill-appearing young infants, sepsis may cause mild or moderate hypothermia, necessitating an evaluation for infection as discussed separately. (See "Approach to the ill-appearing infant (younger than 90 days of age)", section on 'Ancillary studies for infectious etiologies'.)

●Unexplained or resistant hypothermia – Thyroxine (T4), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and serum cortisol should be measured to evaluate for hypothyroidism or adrenal insufficiency in patients with unexplained mild hypothermia or those who are resistant to rewarming. (See "Accidental hypothermia in adults", section on 'Failure to rewarm'.)

Electrocardiogram — A 12-lead electrocardiogram (ECG) should be obtained in all hypothermic patients, and the cardiac rhythm should be monitored continuously during treatment. The development of ventricular fibrillation (VF), pulseless electrical activity (PEA), or asystole is common during resuscitation of children with severe hypothermia. The spontaneous conversion of asystole to VF, and of VF to sinus rhythm, may occur during effective rewarming [24,25].

Hypothermia causes characteristic ECG changes with slowed impulse conduction. This results in prolongation of all the ECG intervals, including RR, PR, QRS, and QT.

J-point elevation may produce a characteristic J or Osborn wave that represents distortion of the earliest phase of membrane repolarization (waveform 1 and waveform 2) [26,27]. Although strongly suggestive of hypothermia, Osborn waves are not reliably present. They can occasionally be seen with other conditions such as traumatic brain injury or subarachnoid hemorrhage. Available software for ECG interpretation is unable to recognize Osborn waves and often misinterprets them as ischemic changes. (See "Accidental hypothermia in adults", section on 'Electrocardiographic changes'.)

Shivering can cause a rhythmic irregularity of the ECG baseline and occasionally of the QRS complex (waveform 3).

Imaging — Radiologic studies in hypothermia are performed based on specific indications:

●Trauma – Victims of multisystem trauma with associated hypothermia should undergo imaging based upon standard guidelines. (See "Trauma management: Approach to the unstable child", section on 'Screening radiographs'.)

●Diving injury – Patients with submersion injury in association with a possible diving injury warrant cervical spine motion restriction and radiographic evaluation, which is described in detail separately. (See "Pediatric cervical spinal motion restriction" and "Evaluation and acute management of cervical spine injuries in children and adolescents".)

●Chest findings – Hypothermic children with abnormal pulmonary findings (eg, tachypnea, cough, and rales) or submersion injury warrant chest radiographs to detect signs of aspiration, bronchopneumonia, pulmonary injury, or pulmonary edema.

●Child abuse – After resuscitation and rewarming, children with physical findings or an inconsistent history suggestive of child abuse (table 3) should undergo further evaluation for child abuse as discussed in detail separately. (See "Physical child abuse: Diagnostic evaluation and management".)

DIAGNOSIS — Hypothermia is diagnosed by measurement of a core body temperature <35°C (95°F) [2]. Clinical staging systems intended for prehospital use are both complex and imprecise [5]. Thus, all hospital care decisions should be guided by core temperature measurement [2,4].

In hypothermia, peripheral (oral, axillary, and cutaneous) sites and "temporal artery" or indirect tympanic thermometers are unreliable and should be avoided [13,28,29]. (See "Fever in infants and children: Pathophysiology and management", section on 'Temperature measurement'.)

Accurate measurement requires use of a low-reading thermometer and is best obtained with a flexible temperature probe, which enables ongoing monitoring [13,14,30]. Potential sites of measurement include:

●Bladder – An indwelling bladder temperature probe may better reflect true core body temperature than the traditionally used rectal temperature and more easily enables ongoing monitoring.

●Rectal – Rectal temperatures, though widely available, are prone to artifact and may lag significantly behind changes in true core temperature. If used, we prefer to measurement with a flexible probe inserted gently to sufficient depth to reach beyond possible masses of cold rectal stool. When a rigid rectal thermometer must be used, it should be inserted at least 10 cm [4 inches] and left in place for several minutes.

●Esophagus – In patients with a secured airway, esophageal temperature probes in the lower third of the esophagus are useful to reflect cardiac temperature.

●Nasopharyngeal – Nasopharyngeal probes can be useful to reflect central nervous system temperatures.

●Central venous – Central venous catheter probes reflect thoracic temperature but must be placed cautiously to avoid triggering fibrillation in the irritable myocardium.

Rewarming methods may cause artificial elevations of temperature measurement [25]. Because of possible rewarming artifacts and time lags, measurement at two central sites (eg, esophagus and bladder) is preferred in critical cases.

DIFFERENTIAL DIAGNOSIS — Pediatric hypothermia may be due to environmental, traumatic, medical, toxic, abusive, or iatrogenic causes [2]. These causes of hypothermia can be grouped by pathophysiology as shown in the table (table 4).

Medical conditions associated with hypothermia include hypoglycemia, hyponatremia, central nervous system pathology (eg, craniopharyngioma, absence of the corpus callosum, intracranial bleeding), endocrine disease (eg, hypothyroidism or adrenal insufficiency), malnutrition, anorexia nervosa, burns, and intoxication [14,30].

Hypothermia due to medical causes is typically mild (core body temperature 32 to 35°C [90 to 95°F]), but patients with these conditions are also at risk for more severe hypothermia after exposure.

A number of etiologies may produce unexpected or unsuspected hypothermia:

●Environmental exposure – Hypothermia occurs even in warm climates such as the southern United States, where cold-related deaths may be twice as common as those due to heat [28]. A child may develop hypothermia when exposed to wet or windy conditions even when the ambient temperature is moderate.

●Trauma and resuscitation – Common causes of hypothermia include injury, transport, and resuscitation, even in warm climates [29], and especially in infants and young children [31]. For example, in one series, hypothermia was present in 29 percent of 461 trauma patients on ambulance arrival; risks included a low coma scale score as well as cold and wet conditions [32]. Brain or spinal cord trauma produces greater risk for hypothermia. Multisystem trauma patients require effective measures to prevent heat loss and early measurement of core temperature during resuscitation. (See "Trauma management: Approach to the unstable child", section on 'Exposure and environment'.)

●Sepsis – Hypothermia in sepsis is especially common in young infants (eg, neonates with disseminated herpes simplex virus infection or invasive bacterial infection) and in older children with immunosuppression or chronic medical conditions. These patients may be ill appearing and have clinical findings (eg, lethargy, hypotension, widened pulse pressure) that should not be seen in mild hypothermia. Such patients warrant standard testing and appropriate cultures. (See "Sepsis in children: Definitions, epidemiology, clinical manifestations, and diagnosis", section on 'Systemic inflammatory response syndrome' and "Neonatal herpes simplex virus infection: Clinical features and diagnosis", section on 'Disseminated disease'.)

●Medications and toxins – Medications and toxins may cause hypothermia by causing vasodilation, altered mental status, or failed thermoregulation. These mechanisms hasten heat loss and increase the risk of environmental hypothermia. Hypothermia may especially accompany overdose of ethanol, benzodiazepines, opioids, and clonidine. The clinical findings of intoxication often overlap with signs of moderate to severe hypothermia (table 5).

Hypothermia may occur in adolescents who drink alcohol or use other drugs, especially in an outdoor setting, but ethanol intoxication itself can be a cause of hypoglycemia and hypothermia in young children. (See "Ethanol intoxication in children: Clinical features, evaluation, and management", section on 'Physical examination' and "Benzodiazepine poisoning", section on 'Clinical features of overdose' and "Opioid intoxication in children and adolescents", section on 'Physical examination' and "Clonidine, xylazine, and related imidazoline poisoning", section on 'Physical examination'.)

●Skin – Especially in children, thermal and chemical burns and even weeping dermatoses may promote significant heat loss. (See "Moderate and severe thermal burns in children: Emergency management".)

●Child abuse and neglect – Cold bathing and forced immersion have been noted as forms of child abuse [21,22]. Because such abuse is easily missed, cases may be more common than reported. Malnutrition, neglect, abandonment, and induced intoxication are other possible causes [23].

Child abuse must be considered when the degree of chilling exceeds the reported time or severity of exposure. Postmortem cooling develops slowly. An unexpected degree of hypothermia may signal child abuse. Other inconsistencies in the history or signs of physical abuse or neglect also suggest abuse. (See "Physical child abuse: Recognition" and "Child neglect: Evaluation and management".)

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 email 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

●Clinical presentation – Hypothermia should be suspected in any child with a history of prolonged exposure to a cold environment but may also occur with severe illness or injury, transport and resuscitation, child abuse, or toxic exposure. Some causes, especially child abuse, may not be readily apparent and must be considered to prevent a missed diagnosis. (See 'Clinical presentation' above and 'Differential diagnosis' above.)

The clinical features seen in hypothermia vary by temperature (table 2). Severe hypothermia may be less obvious than mild or moderate hypothermia. (See 'Clinical presentation' above and 'Diagnosis' above.)

A severely hypothermic child who appears dead may still have significant potential for intact survival with proper resuscitation. (See 'Clinical presentation' above and 'Pediatric considerations' above.)

●Diagnosis – Hypothermia is defined and diagnosed by a core body temperature below 35°C (95°F) (see 'Definition of hypothermia' above and 'Diagnosis' 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)

Accurate measurement of core body temperature requires the use of a low-reading thermometer and is best obtained with a flexible temperature probe. Sites of measurement include the bladder, rectum, esophagus, nasopharynx, and central vein. Important considerations include (see 'Diagnosis' above):

•Rectal temperatures, though widely available, are prone to artifact and may lag significantly behind changes in true core temperature. If used, we prefer measurement with a flexible probe inserted gently to sufficient depth to reach beyond possible masses of cold rectal stool. When a rigid rectal thermometer must be used, it should be inserted at least 10 cm (4 inches) and left in place for several minutes.

•Because of possible rewarming artifacts and time lags, measurement at two central sites (eg, esophagus and bladder) is preferred in critical cases.

●Ancillary studies – Any case of unexplained, prolonged, moderate, or severe hypothermia deserves selected studies and electrocardiogram (ECG) as described above. (See 'Laboratory studies' above and 'Electrocardiogram' above.)

●Differential diagnosis and associated conditions – Hypothermia caused by medical conditions is typically mild on presentation (core body temperature 32 to 35°C [90 to 95°F]) and may occur without environmental exposure. Also, patients with these medical conditions are predisposed to more severe degrees of hypothermia with exposure. Medical conditions associated with hypothermia include (see 'Differential diagnosis' above):

•Sepsis (especially in young infants or neonates)

•Burns

•Hypothalamic disruption (eg, traumatic brain injury, congenital central nervous system anomalies)

•Drug overdose

•Hyponatremia

•Adrenal insufficiency

•Anorexia nervosa

•Malnutrition

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