Resident Eagle is a monthly column profiling the work of top EMS physicians and medical directors from the Metropolitan EMS Medical Directors Global Alliance (the "Eagles"), who represent America’s largest and key international cities. Tentative dates for Gathering of Eagles 2021: June 14–18, Hollywood, Fla. For more see useagles.org.
Hypothermia, defined as a core body temperature below 95ºF or 35ºC, is a potentially deadly condition that can occur in patients with and without environmental exposure.1
Hypothermia usually results in alterations in mental status, cardiovascular compromise, multiple metabolic derangements, and coagulopathies.
While patients exposed to cold temperatures are at risk of hypothermia, this condition can also be seen in patients without environmental exposure. We divide the causes of hypothermia into five categories.
Environmental exposure—Environmental exposure, including those who are wet or immersed in water, is the most common cause. Patients suffering from dementia, psychiatric illness, or intellectual disability may be less likely to seek shelter when needed and are thus at higher risk to develop environmentally induced hypothermia.2 Trauma patients are at especially high risk for environmentally induced hypothermia, and failure to recognize and treat hypothermia in the traumatized patient will decrease survival.3
Inadequate heat production—This is another common cause of hypothermia. Consider this in patients who are very young, very old, or malnourished. Skin disruption such as burns, psoriasis, or exfoliative skin conditions also may lead to hypothermia through inadequate heat production.
CNS depression and dysfunction—These can result from intracranial hemorrhage or spinal cord injury. Sedating drugs such as ethanol and sedative hypnotics can also lead to decreased body temperature.
Endocrine and metabolic conditions—These may also lead to hypothermia, and include hypoglycemia, Wernicke encephalopathy, and adrenal, thyroid, or pituitary dysfunction.
Sepsis—Sepsis is a common potential cause of hypothermia; always consider it in any patient with altered mental status, hypotension, and bradycardia, especially in the very young and very old.
Common ECG Findings
Hypothermic patients may present with abnormal ECGs, and there are some ECG abnormalities commonly seen in the condition.4 Patients with mild hypothermia, defined as body temperature between 32–35ºC, may have shivering artifact or an irregularity in their baseline caused by shivering. This finding may disappear as patients become more hypothermic and lose the ability to shiver.
Decreased body temperature leads to conduction and metabolic abnormalities, which causes bradycardia and arrythmias. Most classically seen is slow atrial fibrillation. Decreased temperatures also cause delayed conduction in the atria, AV node, and within the His-Purkinje system and the ventricle, resulting in a prolonged PR interval, widened QRS, and a prolonged QT interval.
Atrial fibrillation is common in hypothermic patients with body temperature less than 32ºC or 90ºF. A highly specific ECG finding in patients with hypothermia is the presence of J-waves, or Osborn waves. These are present at the end of the QRS complex, and their amplitude correlates to the degree of hypothermia.
Hypothermia can also lead to deadly arrythmias such as ventricular tachycardia, ventricular fibrillation, and asystole. These arrythmias can lead to cardiac arrest. The risk for cardiac arrest increases as core body temperature drops below 32ºC but is considerably higher when body temperature dips below 28ºC/82ºF. While risk of cardiac arrest increases as body temperature drops, it is important to remember that patients may also experience dangerous arrythmias during rewarming.
Immediate Steps to Take
Patients may lose heat via four mechanisms: evaporation as moisture leaves a wet patient; radiation as heat is lost to the atmosphere; conduction as heat is transferred from the body onto a cold surface; and convection as cold air passes over the body. Rewarming methods must immediately focus on reversing these processes.
To avoid further heat loss and begin rewarming, remove wet clothing, dry the patient, and wrap them in warm blankets. If available, place warming packs to the axilla and chest before wrapping the patient. Thermal foil blankets provide excellent insulation and should be used as the first layer of insulation if stocked on the unit.
Hypothermic patients are critically ill, so rapid transport while evaluating for injury is important in as warm an ambulance as possible. Remember to handle with care, as hypothermic patients are at increased risk for arrhythmias, especially with increased movement during transfer. Heat the ambulance and place the patient on the monitor.
Patients may be altered or comatose and need a definitive airway placed. Otherwise provide supplemental oxygen to keep saturation above 90%. Always check a blood glucose, as alcoholics comprise the largest percentage of exposure-induced hypothermia and are at risk for concomitant hypoglycemia.
Additionally, hypoglycemia may result in a diabetic patient developing altered mental status and failing to seek shelter as temperatures drop. Of note, it may be difficult to rewarm the patient until hypoglycemia is treated.
Palpating a pulse in hypothermic patients can be challenging, and inappropriate CPR can lead to arrythmias.5 Always carefully check for a pulse and signs of life such as breathing or movement for a full 60 seconds before initiating CPR.
It is important to remember that medications and electricity do not work well in hypothermic patients. However, the most current ACLS recommendations are to follow standard protocols for defibrillation and use of antiarrhythmics.6
Mistakes to Avoid
Though these patients are critically ill, treatment differs from critically ill patients with normal body temperature.4 Although obtaining IV access is done in essentially all critically ill hypotensive patients, do not administer aggressive volume resuscitation in cases of hypothermia. Though these patients may be volume-depleted, they are at risk of pulmonary edema due to cardiac dysfunction and decreased cardiac output.
Similarly, do not use vasopressors for hypotension in these patients. Pressor use may lead to arrhythmias and worsening peripheral perfusion in patients already suffering from peripheral vasoconstriction and at risk for frostbite.3
Hypothermic patients may be unstable and bradycardic, but typical treatment for unstable bradycardia usually will not help and may worsen the patient’s condition by causing deadly arrhythmias. Do not use atropine or transcutaneous pacing in hypothermic patients. While hypothermia may lead to altered levels of consciousness, do not assume altered mental status is due to hypothermia alone.
Remember, infection, stroke, sedating drugs, and metabolic disturbances such as hypoglycemia all may lead to hypothermia. Similarly, there may be little history available for precipitating events.
Finally, do not forget to consider concomitant trauma and/or cervical spine injury in these patients. Patients should be transported in spinal precautions with any signs of trauma or concern for traumatic injury.
1. Brown DJA, Brugger H, Boyd J, Paal P. Accidental Hypothermia. New Eng J Med, 2012 Nov 15; 367: 1,930–8.
3. Haverkamp FJC, Giesbrecht GG, Tan E. The prehospital management of hypothermia—An up-to-date-overview. Injury, 2018 Feb; 49(2): 149–64.
4. Slovis C, Jenkins R. ABC of clinical electrocardiography: Conditions not primarily affecting the heart. BMJ, 2002 Jun 1; 324(7,349): 1,320–3.
5. Danzl DF, Pozos RS, Auerbach PS, et al. Multicenter Hypothermia Survey. Ann Emerg Med, 1987 Sep; 16(9): 1,042–55.
6. Panchal AR, Bartos JA, Cabanas JG, et al. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary and Emergency Cardiovascular Care. Circulation, 2020 Oct 20; 142(16): Suppl 2, S366–S468.
Sidebar: Hypothermia Dos & Don’ts
5 Things to Do in the Field
Remove wet clothing, dry the patient, & wrap in warm blankets;
Rapidly transport while evaluating for injury in a warm ambulance;
Place the patient on the monitor;
Provide supplemental oxygen;
Check blood glucose.
5 Things Not to Do in the Field
Administer aggressive volume resuscitation;
Use vasopressors for hypotension;
Use atropine or transcutaneous pacing;
Assume altered mental status is due to hypothermia;
Forget to consider concomitant trauma and/or C-spine injury.
Maddison S. Gowder, MD, is an emergency medicine resident at Vanderbilt University Medical Center in Nashville, Tenn.
Clifford L. Freeman, MD, is a flight physician at Vanderbilt University LifeFlight.
Corey M. Slovis, MD, is professor of emergency medicine at Vanderbilt University Medical Center. He is medical director for the Nashville Fire Department and Nashville International Airport.