Definition:

Patient with impaired thermoregulation can develop hypothermia in relatively warm environments

Most frequent cause is environmental exposure

Accidental hypothermia is an unintentional core body temperature of < 35°C when heat loss to surroundings is greater than heat generation

Management should be guided by symptoms , temperature ranges have limited clinical utility

Symptoms and core body temperature do not always correlated

Multiple classification systems have been used to delineate severity of hypothermia, some based on core body temperature and ssome based on symptoms

Moderate (HT II)- Impaired conscious, may or may not be shivering (approximate core temperature <32°C-28°C)

Cold diuresis: polyuria caused by vasoconstriction and a decrease in ADH production

Have a high degree of suspicion for hypothermia in elderly, undomiciled, and intoxicated patients

Patients with any of the following should have their core temperature measured

Paradoxical undressing: a phenomenon in which the patient undresses despite significant hypothermia, believed to be caused by peripheral vasodilation secondary to autonomic dysfunction causing the sensation of skin warmth in combination with altered mental status. Some degree of undressing is seen in up to 30% of fatal hypothermia cases ( Brändström 2012

Psuedorigormortis: increase in muscle tone due to a shivering like response, can lead to compartment syndrome of the extremities

Hypothermia with altered mental status can mimic, or coexist with, many other derangements

Sepsis should be high on the differential for unexplained hypothermia

Primary and secondary trauma survey if altered mental statue or unclear history

Esophageal probe: best option, falsely high with warmed air ventilation or thoracic lavage

Take care when moving hypothermic patients as jostling can precipitate ventricular dysrhythmias. This concern should not prohibit necessary patient care

Cooling decreases cerebral oxygen requirements allowing for neurologically intact survival after prolonged periods of hypoperfusion. Patients should be actively resuscitated to a core temperature of >32 ° C before termination is considered

Active rewarming should continue until a core temperature of >32°C regardless of whether ROSC is achieved prior to this point ( Zafren 2018

Active internal rewarming is required; external rewarming is less effective in patients in cardiac arrest

ECMO is the best option for severely hypothermic patients without signs of life who do not respond to initial resuscitative efforts. It has been shown to improve neurologically intact survival (48% to 63% survival with ECMO, <37% without ECMO) ( Brown 2012

Ventricular dysrhythmias are often refractory to electricity when the patient is still hypothermic

There is a theoretical concern that IV medications will not be effective and will accumulate to toxic levels in the severely hypothermic patient. Some experts recommend withholding vasopressors, or limiting doses, until after the patient is warmed to > 30°C ( Brown 2012

AHA ACLS guidelines: “It may be reasonable to consider administration of a vasopressor during cardiac arrest according to the standard ACLS algorithm concurrent with rewarming strategies (Class IIb, LOE C)”

Irritation of the myocardium from the guide wire can result in dysrhythmias

Peripheral access preferred if can rapidly and reliably be obtained

Consider the use of a mechanical compression device if available as prolonged, high quality compression may be required

Continue compressions until the patient is warm, shows signs of life, or ROSC is achieved

Peripheral pulses are unreliable in all cardiac arrest and more so in hypothermic arrest due to vasoconstriction

Follow standard management as with any cardiac arrest

It is important to determine whether hypothermia preceded arrest. Hypothermia as the cause of arrest has positive prognostic implications while hypothermia secondary to arrest is rarely survivable

Passive and active external rewarming are the mainstays of treatment

Atrial fibrillation and atrial flutter usually resolve with rewarming

Sinus bradycardia is a normal physiologic response and should be treated with rewarming, atropine is usually not effective

Hypotensive patients should be aggressively fluid resuscitated as they are usually volume down due to hypothermic diuresis and fluid shifts

IV fluids should be warmed to 40°C. They do little to warm the patient but room temperature fluids can lead to further heat loss

Monitor for bronchorrhea and depression of mental status

Further imaging as indicated by history of trauma

Look for pulmonary edema and aspiration pneumonia

The risk for ventricular arrhythmias increases at < 32°C, and substantially increases at < 28°C

May be seen in other settings ( Wang 2011

Bradycardia is a normal physiologic response to hypothermia. Heart rate and oxygen consumption decrease by 50% at core temp of 28°C. (Danzl 2007)

Consider blood cultures and cortisol level to assess for other contributing factors

VBG or ABG if clinically indicated

Coagulation panel may, however, be normal as blood is warmed prior to testing and factors are temperature dependent

K > 10 mEq/L carries very poor prognosis in patients in cardiac arrest ( Brown 2012

Prevent hypoglycemia. Hypothermia lowers metabolic rate and makes it difficult for the patient to generate heat. Any amount of hypoglycemia will further exacerbate this

Labs (think of the trauma triad of death: hypothermia, coagulopathy, and metabolic acidosis)

Used in any patient that is hemodynamically unstable

Peritoneal dialysis (1-3°C per hour, may be high risk in the emergency setting)

The patient must be able to generate their own body heat

Rewarming can be considered in three main categories. The method of rewarming is based on individual patient factors and available local resources

If patient fails to rewarm 1°C/hour, consider other contributing factors or causes (ie sepsis, hypothyroidism etc)

Hypothermic patients in cardiac arrest may benefit from standard post arrest targeted temperature management, but there is limited evidence to guide practice here

Rewarming should focus on warming the core to minimize this risk

May occur due to peripheral vasodilation and return of chilled blood to the core, though there is controversy whether this is a clinically significant phenomenon

A drop in core temperature after initiation of rewarming

Gastric, colonic, and bladder irrigation are not recommended

Termination should also be considered in patients with K > 12 mEq/L

Patients with a core temp >32°C with persistent asystole are unlikely to achieve ROSC and termination should be considered

In general, resuscitative efforts should continue until the patient has been successfully rewarmed (>32°C)

Survival after 6.5 hours of CPR with active internal rewarming has been reported ( Lexow 1991 ) as has survival after a core temperature of 9°C ( Vassallo 2015

Pulmonary edema is the most common cause of in hospital mortality among these patients ( van der Ploeg 2010

Patients with severe hypothermia or hypothermic arrest who are successful rewarmed and resuscitated should be admitted to the ICU. Many patients will develop organ failure within the first 24 hours of admission

Mild hypothermia can usually be rewarmed and discharged home as long as protection from repeat exposure is guaranteed (i.e. do not discharge a homeless patient who presents with mild hypothermia unless they are going to a safe, heated environment)

Hypothermia is neuroprotective and patients can survive prolonged periods of cardiac arrest. Termination of resuscitative efforts in cardiac arrest should not considered until the patient is >32°C or has a K > 12 mEq/L

Active internal rewarming is the keystone of treatment for unstable hypothermic patients. Utilize available resources including ECMO to effectively warm your patient