Hypothermia Cardiac Arrest

Hello, and thank you for your MedicASK regarding the administration of ACLS medication in a hypothermic cardiac arrest.

As you may recall, there used to be a hypothermia cardiac arrest medical directive that was independent of the medical cardiac arrest medical directive. Prior to the ALS PCS v. 5.0, the hypothermia cardiac arrest medical directive was maximum one analysis/defibrillation and early transport to the closest hospital, without the use of any ACLS medication. This is because despite epinephrine and vasopressin being shown to improve coronary artery perfusion pressure in animals, there is concern that administration of these medications, including procainamide and lidocaine can accumulate to toxic levels in the peripheries if they are administered repeatedly in the severely hypothermic patient. For these reasons, in hospital, these medications are often withheld if the core body temperature is <30 degrees Celsius. Once the patient's core body temperature is above 30 degrees Celsius, IV medications may be administered with increased intervals between doses (https://www.ahajournals.org/doi/full/10.1161/circ.102.suppl_1.I-229).

Since the medical directives merged, hypothermia is still listed as a primary clinical consideration for early transport after a minimum of one analysis (and defibrillation if indicated) once an egress plan is organized.

There are currently no contraindications to administer epinephrine or antiarrhythmics in a cardiac arrest secondary to hypothermia. The reason for the change is that we do not have the proper tools in the pre-hospital setting to assess an accurate core body temperature. Therefore, not treating based off of a potentially inaccurate number limits care and the decision was made to provide cardiac arrest management to all patients, including those who are hypothermic as the benefits outweigh the risks.

The preferred method of measuring core body temperature in hypothermia is esophageal in a patient whose airway is protected/secure. Rectal is not recommended until the patient is moved to a warm environment as is further exposes them to the cold. Oral thermometers are only useful to rule out hypothermia, and infrared tympanic thermometers are essentially useless in a hypothermic patient.

That said, it is key to note the following during your assessment/treatment:

Swiss staging model for hypothermia:

• I – clearly conscious and shivering
• II – impaired consciousness without shivering
• III – unconscious
• IV – not breathing
• V – death due to irreversible hypothermia

Resuscitation efforts in hospital:

• Move patient gently if <32 degrees due to risk of triggering VF (risk is overstated). Keep the patient in a horizontal position if possible
• No adrenaline or other drugs until >30C
• Between 30-35C double the dose intervals of ACLS drugs
• Shock VF up to 3 times if necessary, then no further shocks until T>30C
• ‘Not dead until warm and dead’ (30-32C)

It is also crucial to do the following when warming the patient:


Passive warming – useful in conscious patients who are able to shiver (1.5C per hour)

• Keep dry
• Warm environment
• Insulation with blankets (e.g. aluminum foil) and hat (remove all wet clothing prior to insulating with blankets)

Afterdrop phenomenon: a drop in core body temperature during rewarming may occur a consequence of peripheral vasodilation and release of cold peripheral blood to the body core. It is not usually significant (https://litfl.com/hypothermia/).

BLS PCS v. 3.4 Cold Injury Standard (p. 122):

• Remove the patient from the cold as soon as it is safe to do so after completing the primary survey
• For patients with known or suspected hypothermia, pulse and respirations checks should be performed for up to ten seconds
• Attempt to determine duration of exposure and type of exposure
• If hypothermia is known or suspected, attempt to determine the severity of hypothermia
• The presence or absence of shivering is an important indicator of severity of hypothermia. If shivering is minimal or absent and level of consciousness is decreased or mental status is markedly altered, assume core temperature is below 32 degrees Celsius

Should you wish to provide further treatment, withhold treatment, or have a consultation with one of the physicians, the patch line is always open and available for you to call and discuss the above information.

We hope this helps you in your practice moving forward! If you would like to refresh your memory on hypothermia, here is the link to access Professor Popsicle's webinar from 2022 CME: https://mediclearn.rppeo.ca/course/view.php?id=690