Approach

Initial management involves assessing and managing the patient's airway, breathing, and circulation, and preventing further heat loss.[45]​​[55]​​ Get urgent support from the critical care team for any patient with severe hypothermia.

​Be aware that vital signs may be very difficult to detect in a patient with hypothermia, especially in the prehospital setting; a very hypothermic patient may appear dead but still survive with resuscitation.[20]​​[45]​​[48]​​[49]​​ Do not declare a patient dead prior to full resuscitative measures and aggressive rewarming, unless in the case of nonsurvivable traumatic injury or rigor mortis.[45]​​​​

Supportive measures depend on the patient’s clinical status and severity of hypothermia, and include:[20]​​[45]​​[48][55]

  • Removal of wet and cold clothing and insulation (e.g., with a warm blanket)

  • Advanced airway management

  • Heated humidified oxygen and warm intravenous fluids, particularly once rewarming has been started

  • Management of cardiac arrhythmias (with the exception of ventricular fibrillation [VF], these are likely to improve without treatment as the patient’s core temperature increases)

  • Management of hypoglycemia

  • Monitoring of core temperature and hemodynamic status during rewarming.

Choice of rewarming strategy (passive external, active external, active internal/core) is based on the patient’s core temperature and clinical features; a combination of techniques may be used.

Hypothermia in the prehospital setting

The prehospital management of the hypothermic patient should be focused on:[20]​​[45]​​[48][55]

  • prevention of further drops in body temperature (i.e., carefully removing the patient from the cold environment, and removal of any wet or cold clothes),

  • stabilization of the patient following basic life support (BLS) and advanced cardiovascular life support (ACLS) protocols,

  • maintenance of the patient in a supine position if they have features of moderate or severe hypothermia (e.g., they have stopped shivering or have a reduced level of consciousness),

  • insulation of the patient and stabilization of the core temperature by starting rewarming measures (as long as there is adequate monitoring in place to detect any arrhythmias caused by rewarming), and

  • transfer of the patient to an appropriate center for rewarming; where available, this should be to an extracorporeal life support (ECLS) center for patients with hemodynamic instability or severe hypothermia and patients in cardiac arrest or at imminent risk of cardiac arrest.

Patients are at risk of imminent cardiac arrest if they have any of the following:[20]

  • Core temperature <86°F (<30°C), or <89.6°F (<32°C) if the patient is frail with multiple comorbidities

  • Ventricular arrhythmia

  • Systolic blood pressure <90 mmHg.

If an ECLS center cannot be reached within 6 hours, non-ECLS rewarming should be started in a peripheral hospital.[20]

It is important to be gentle during patient transport as cardiac excitability makes the patient's heart susceptible to arrhythmias.[48]​

Exercise is not recommended as a rewarming strategy (unless core temperature is above 95°F [35°C]) due to the risk of fatal arrhythmias secondary to peripheral vasodilation.[56] Exercise can also cause cool blood to return to the central circulation.[56]

Cardiac arrest

Cardiopulmonary resuscitation (CPR) should be initiated promptly and without interruption in patients where vital signs cannot be detected after 1 minute and in patients with a nonperfusing rhythm (including VF, ventricular tachycardia [VT], and asystole).[20][48]​​​ Where possible, ECG monitoring, end-tidal CO₂, and ultrasound should also be used to detect cardiac arrest.[20][48]

Be aware that vital signs may be very difficult to detect in a patient with hypothermia, especially in the prehospital setting; a very hypothermic patient may appear dead but still survive with resuscitation.[20]​​[45]​​[48]​​[49]​​ Do not declare a patient dead prior to full resuscitative measures and aggressive rewarming, unless in the case of nonsurvivable traumatic injury or rigor mortis.[45]​​

The American Heart Association (AHA) recommends providing standard BLS and ACLS treatment for patients with accidental hypothermia, combined with the appropriate rewarming techniques in line with the patient's clinical status.[45]​​ In some cases, patients may be unresponsive to cardiovascular drugs, pacemaker stimulation, and defibrillation, although there is an absence of robust data to support this; defibrillation should still therefore be attempted for VF and VT.[45]​​ If defibrillation fails to restore a normal heart rhythm after a single shock, continue adhering to standard BLS and ACLS protocol; there is uncertain evidence regarding the effectiveness of deferring defibrillation until a target core temperature is achieved.[45]​​

Vasoactive drugs should generally be avoided until patients have been rewarmed to at least 86°F (30°C).[48] This is because drug metabolism and protein binding are both affected in hypothermia so drugs that are administered in patients with very low core temperatures may reach toxic levels with rewarming. However, the AHA advises that epinephrine (adrenaline) administration is reasonable in cardiac arrest as part of the ACLS algorithm.[45]​​

For a patient in cardiac arrest, hyperkalemia can indicate that hypoxia preceded hypothermia (e.g., if the patient was found in an avalanche).[19]​ Severe hyperkalemia and very low initial core temperatures may predict unsuccessful resuscitation efforts; serum potassium is part of the HOPE (Hypothermia Outcome Prediction after ECLS rewarming for hypothermic arrested patients) score for prognostication of successful rewarming.[20]​​[45]​​[48]​​ [ Hypothermia outcome prediction after ECLS (HOPE) score Opens in new window ] ​ The Wilderness Medical Society states an initial serum potassium >12 mEq/L (>12 mmol/L) is associated with irreversible death if the patient is in cardiac arrest.[48]

See Cardiac arrest.

Airway

If the patient cannot maintain or protect the airway, it should be secured with an advanced airway (e.g., tracheal tube or supraglottic airway device). Advanced airway placement should be attempted only by those with appropriate training and experience.[20][45]​​​​ Patients with an advanced airway should be ventilated at half the standard normothermic rate.[48]

Advanced airways should allow passage of a gastric tube: this allows placement of an esophageal temperature probe as well as decompression of the stomach.[48]​ An esophageal probe is the preferred method of core temperature measurement in patients with hypothermia as it correlates well with the temperature of the pulmonary artery.[19][20][48]

It is important to note that endotracheal intubation may cause VF in severe hypothermia. However, this risk is small and the benefits of intubation when indicated outweigh the risk of VF.[19][48]

Placement of an endotracheal tube may be more difficult in cold environments due to hypothermia-induced trismus.[19][48]​ If laryngoscopy is not possible, fiber-optic intubation or cricothyroidotomy can help facilitate placement of an endotracheal tube, but it may be preferable to consider a supraglottic airway device until the patient is moved to a warm environment.[48]

Breathing

Patients with hypothermia can receive heated humidified oxygen therapy, regardless of their oxygen saturations.[48]​ This reduces heat loss through respiration, but is not effective as a rewarming method on its own; it should be used as an adjunct to other rewarming techniques.

Circulation

In moderate and severe hypothermia, circulating blood volume is reduced due to vasoconstriction.[48]​ Circulatory access via a peripheral intravenous catheter is the preferred method, though this may be difficult to achieve in hypothermic patients because of cold-induced peripheral vasoconstriction.[48]​ If not immediately possible, intraosseous access should be established instead.​

​Patients should be infused (intravenously or intraosseously) with normal saline, warmed to 104°F to 107.6°F (40°C to 42°C).[48]​ Warmed intravenous fluids help to prevent heat loss but do not actively rewarm the patient. Infusing warmed intravenous fluid also offers the additional advantage of improved absorption of administered drugs. Lactated Ringer solution should be avoided as the liver will not be able to metabolize lactate in hypothermia.[48]

It is important that patients are carefully monitored for signs of fluid overload and volume depletion. It is likely that large volumes of fluid will be required because vasodilation during rewarming causes expansion of the intravascular space and subsequent hypotension.[19][48]​ Warmed intravenous fluids should ideally be administered via boluses, guided by vital signs (heart rate and blood pressure) as opposed to continuous infusion, as this will help avoid issues with fluid cooling or lines freezing.[19][48]

Vasoactive drugs are generally avoided when managing hypotension in a patient with significant hypothermia, unless the hypotension is due to other causes (e.g., sepsis) or in highly specialist scenarios (e.g., if the patient is undergoing ECLS).[20]​ Always seek urgent advice from the critical care team before giving vasoactive drugs. If indicated, vasoactive drugs should be withheld until the patient’s core temperature is at least ≥86°F (≥30°C).[48]​ However, the AHA advises that epinephrine administration is reasonable in cardiac arrest as part of the ACLS algorithm.[45]​​

All arrhythmias apart from VF (particularly atrial arrhythmias) are likely to improve without treatment as the patient’s core temperature increases.[19][20][48]​ However, if the patient has bradycardia and hypotension that is disproportionate to their hypothermia, consider transcutaneous pacing.[48]​ See Overview of dysrhythmias (cardiac).

Dextrose

Treat hypoglycemic patients with dextrose.[48]​ Hypoglycemia can stop shivering (because the central control of shivering is dependent on glucose), leading to subsequent heat loss.[53]​ Where blood glucose testing is not available and hypothermic patients present with an altered level of consciousness, empiric dextrose should still be initiated.[48]​ See Nondiabetic hypoglycemia.

Monitor blood glucose even after the patient is normoglycemic as rebound hypoglycemia may develop when normal insulin production resumes.

Insulin should not initially be started in patients with hyperglycemia as high blood glucose has not been shown to be detrimental in patients with hypothermia.[48]​ Monitor blood glucose and seek expert advice if: hyperglycemia is worsening; there is associated ketosis; hyperglycemia persists after successful rewarming; or the patient has type 1 diabetes.

Rewarming

The optimal rewarming method depends on the severity of hypothermia and the patient’s clinical condition. If the patient has:[19][20]​​[45]​​[48]​​[49]​​​

  • Mild hypothermia (core temperature 90°F to 95°F [32°C to 35°C]), start passive external rewarming methods initially. Active external rewarming methods should be used if there is an insufficient response to passive methods and are useful in both shivering and nonshivering patients. Mild hypothermia can be managed in a prehospital setting; patients do not require transfer to hospital provided they are uninjured, alert, and shivering.

  • Moderate or severe hypothermia (core temperature ≤90°F [≤32°C]), use external (active and passive) and internal rewarming methods. Get urgent support from the critical care team for any patient with severe hypothermia.

  • Severe hypothermia (core temperature ≤86°F [≤30°C]) and cardiac arrest, extracorporeal rewarming is the preferred method as it allows for rapid rewarming. Patients with severe hypothermia, hemodynamic instability, or witnessed out-of-hospital cardiac arrest and those at risk of imminent cardiac arrest should be transferred to centers capable of providing ECLS. Patients are at imminent risk of cardiac arrest if they have any of the following: core temperature <86°F (<30°C), or <89.6°F (<32°C) if the patient is frail with multiple comorbidities; ventricular arrhythmia; systolic blood pressure <90 mmHg.

Patients with severe trauma should be treated aggressively with active rewarming, regardless of the severity of their hypothermia; hypothermia is associated with higher mortality among trauma patients.​[3][26][48]

It is critical that patients with moderate or severe hypothermia have their core temperature and hemodynamic status continuously monitored during rewarming.[48]​ Heat redistribution within the body can cause a continued fall in core temperature after removing the patient from a cold environment (also known as afterdrop). Avoid hyperthermia during and after rewarming.[19]

Monitor potassium: hypokalemia may occur as a result of hypothermia or the associated treatment and hyperkalemia may occur during rewarming. Serum potassium is part of the HOPE (Hypothermia Outcome Prediction after ECLS rewarming for hypothermic arrested patients) score for prognostication of successful rewarming; severe hyperkalemia may predict unsuccessful resuscitation efforts.[20]​​[45]​​[48] [ Hypothermia outcome prediction after ECLS (HOPE) score Opens in new window ]

External rewarming methods

External rewarming methods may be passive or active.[19]

Passive methods involve reducing further evaporative heat loss through removal of wet clothing and insulating the patient (e.g., with warm blankets and dry clothes).​[45]​​[48]​​[55]​ Patients may be given high-calorie food and warm sweet drinks if alert and able to safely consume food and fluids orally; these do not rewarm the patient but will supply energy for shivering.[19][55]​ Active movement (e.g., standing, walking) should also be encouraged if possible in patients with mild hypothermia and shivering who have had adequate time to rewarm.[19][48]

Active external rewarming may involve using electric heat pads or blankets, hot water bottles, chemical heat pads, or forced air warming.[48]

Internal rewarming methods

Active internal (also known as active core) rewarming, used alone or in combination with active external rewarming, is the most aggressive strategy and is indicated in moderate to severe hypothermia. Active internal rewarming methods include: lavage with warmed normal saline, ECLS, veno-venous rewarming, continuous renal replacement therapy (CRRT), and hemodialysis.[19]

ECLS rewarming provides sufficient circulation and oxygenation while the core body temperature is increased at a rewarming rate of 39.2°F to 50°F (4°C to 10°C) per hour.[19]​ Patients with severe hypothermia, hemodynamic instability, or witnessed out-of-hospital cardiac arrest and those at risk of imminent cardiac arrest should be transferred to centers capable of providing ECLS.[20][48]

If the patient is in cardiac arrest, ECLS rewarming is the preferred method of active internal rewarming.[20]​​[45]​​[48]​​​ For patients with hemodynamic instability, ECLS rewarming should be considered as it may provide some benefit.[48]​ Evidence suggests that ECLS rewarming offers a better survival outcome than other treatment modalities.[19][57][58]​​ Preferably, ECLS rewarming should be performed with extracorporeal membrane oxygenation (ECMO) over cardiopulmonary bypass (CPB).[48]

ECLS requires heparinization, undesirable in the hypothermic patient and in patients with severe trauma who are already at increased risk of coagulopathy.[2][20]​​​​[59]​ Low- and no-anticoagulation protocols are being investigated in adults at high bleeding risk.[60]

Other methods of active internal rewarming (lavage, veno-venous rewarming, CRRT, and hemodialysis) are less effective and may only be recommended where ECLS rewarming is unavailable.[19]

Irrigation with normal saline (lavage) can be peritoneal, thoracic, gastric, bladder, or colonic, warmed to 104°F to 107.6°F (40°C to 42°C).[19][48]

Continuous veno-venous hemofiltration (CVVH), a type of CRRT, may be considered in patients with hyperkalemia (e.g., due to rewarming or rhabdomyolysis) or acidosis.[61]

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