There are two important questions regarding the patient with hypothermia

• Is there a cardiorespiratory arrest?
• What is the core temperature?

The algorithm for hyperthermia utilizes these two questions to manage patients.

Hypothermia Algorithm

Managing Non-Cardiac Arrest Hypothermia

In the hypothermic patient with a pulse, the main goal is to prevent ongoing heat loss and begin the rewarming process. This will prevent progression to cardiac arrest. Treatment involves:

• Prevent ongoing heat loss by removing wet clothing and providing insulation from cold
• Provide rewarming treatment
• Monitor vital signs, including core temperature and cardiac rhythm
• Transport to a higher level of care

Keep patients flat if possible as there is hypovolemia secondary to abnormal hemodynamic functioning. Do not cause excessive motion; however, do provide necessary resuscitation interventions such as CPR or intubation. While movements may precipitate VF, especially at a temperature below 30 degrees C, providing care is necessary.  The temperature should be measured via internal readings (i.e., tympanic membrane or rectum). Patients should have continuous cardiac monitoring; if the skin temperature is too cold for adhesive, adhere electrodes with sterile needles. 

Specific Interventions

• Use passive rewarming methods (i.e., warm blankets) for mild hypothermia (34-36 degrees C)
• Use active rewarming methods for moderate hypothermia with a palpable pulse (30-34 degrees C). An example is a forced, warm-air device.
• Use active internal rewarming methods for severe hypothermia with a palpable pulse (under 30 degrees C). The preferred method is cardiopulmonary bypass, but other options include thoracic cavity lavage with warm water or extracorporeal bypass. Supplementary therapies included warm IO or IV fluids and humidified air.
• Never delay needed therapies for fear of stimulating VF 

Warming Techniques

Passive warming

This should be used for patients with intact shivering (i.e., over 32 degrees C). These include blankets and reflective metal wraps. This is a slow therapy as core temperature increases by about 0.25 degrees C each hour. Passive warming should also be used as an adjunct treatment for patients with moderate and severe hypothermia. 

External active warming

These more active but noninvasive options include heated devices (i.e., heated blankets, chemical warm packs), radiant heat, forced air, and heated water. Be aware that hot devices should not be placed directly on the skin as this can lead to skin burns, especially in hypothermic patients with reduced sensation. These devices should be placed in the axilla and the groin, leaving the chest, arm, and neck available for resuscitation efforts. External active warming increases core temperature by about one degree C each hour.

Hypothermia First Aid

Internal active warming

Patients with severe hypothermia will require this therapy, including infusion of warmed IV fluid and humidified warm oxygen. More invasive treatments include warm lavage of the internal organs. 

In a cardiac arrest patient, 

• Simultaneously use multiple warming techniques while providing CPR
• Begin with simple techniques and increase complexity as these become available 
• Never delay urgent resuscitative treatments due to fear of VF precipitation

Note that patients with severe hypothermia should also receive both forms of external warming.

Warm IV fluids

Fluids are warmed to 42-44 degrees C and infused at 150-120 ml/h. Patients should be monitored for fluid overload, and urine output will need to be monitored. 

Humidified warm oxygen

The air is heated to 42-46 degrees C. This is an important part of internal active warming. It can increase core temperature by 1-1.5 and 1.5-2 degrees C each hour at 40 and 45 degrees C, respectively.

Warm lavage

The preferred treatment is peritoneal lavage with fluid free of potassium chloride and warmed to 43 degrees C. Additionally, lavage of the intestines, bladder, thorax, and heart can be options. Lavage of the thorax can be accomplished using two thoracostomy tubes.

Cardiac bypass

This is the most effective at rewarming and can be used in severe hypothermia and associated cardiac arrest. It rapidly increases core temperature by one degree C every 5 minutes. As this allows support of perfusion as well as ventilation and oxygenation, it is very effective.

Managing Cardiac Arrest-Associated Hypothermia

Responders will have to make some adjustments to resuscitation efforts in the hypothermic cardiac arrest patients. 

Initial Treatment for Hypothermia

As with other patients in cardiac arrest, the management of airway, breaths, and circulation is still of paramount importance. Responders should be aware that respiration and pulse rates may be abnormally slow in the hypothermic patient. In those who appear “clinically dead,” CPR should be started immediately, including rescue breaths. The temperature does not need to be verified before treatment is begun. If possible, responders should also provide warming techniques such as humidified warm oxygen in conjunction with bag-mask ventilations. 

Studies do not show the best temperature to begin defibrillation in hypothermic patients. While significant hypothermia may be associated with increased or even refractory VF, studies also show that hypothermia may be associated with improving response to defibrillation. 

Defibrillation should not be withheld in hypothermic patients. If there is a shockable rhythm, defibrillation should be given. Resume CPR immediately as would be done in any case of cardiac arrest. If the arrhythmia persists, it is reasonable to continue repeat defibrillation attempts while simultaneously attempting to warm the patient. (Class IIb, Evidence level C). 

Advanced Treatment for Hypothermia

Management of the airway is similar to other cases of cardiac arrest. An advanced airway should be placed as quickly as possible if needed. It also provides a conduit to deliver warmed humidified oxygen, as well as help minimize aspiration events. 

Of course, there will also be a primary focus on warming the patient. While traditionally it was thought that the hypothermic heart is not responsive to conventional resuscitative therapies, however, research has not proved this to be true. 

There is a difference in the metabolism of medications. This can lead to the concern that in hypothermic patients, medications can reach toxic levels if repeatedly dosed. This can cause providers to withhold medications in patients with severe hypothermia. Recent research suggests that vasopressors increase the likelihood of ROSC in these patients compared to place. Smaller animal-based research indicates that using the algorithm for cardiac arrest medications with defibrillation improved outcomes in hypothermia compared to defibrillation alone. These are small case reports, so based on the available literature, it is reasonable to provide vasopressors to hypothermic patients with associated cardiac arrest. (Class IIb, Evidence level C). 

Defibrillation should be used for pulseless ventricular arrhythmias. Clinicians should be aware that significant bradycardia is often physiological and should not be managed with pacing.

Warming in the hospital includes warming humidified air, warmed IV fluids, warmed peritoneal lavage, and extracorporeal warming with bypass procedures. Extracorporeal CPR (or ECPR) with extracorporeal membrane oxygenation and cardiopulmonary bypass can also be used if experience and equipment are available. This allows more rapid warming of the patient and can be a temporizing maneuver until left ventricular assist devices or heart transplantation can occur. Studies indicate that ECPR provides survival benefit with improved neurologic function compared to traditional CPR. It is particularly beneficial in hypothermic patients who may have a reversible cause of cardiac arrest that can be reversed in the period of ECPR. (Class IIb, Evidence level C-LD).