A 60-year-old man was brought in by EMS after he was found unresponsive in a park on a cold December morning. EMS called it in as a cardiac arrest.
The patient was intubated, shocked, received one dose of epinephrine, and had continuous CPR before arriving at the ED. He had a core temperature of 22°C on arrival.
What caused this patient's symptoms?
Find the diagnosis and case discussion on p. 31.
Diagnosis: Accidental Hypothermia
Accidental hypothermia is an unintentional core temperature below 35°C, while mild hypothermia is a core temperature of 32.2-35°C, moderate is 28-32.2°C, and severe is under 28°C. (N Engl J Med 1994;331:1756.) Hypothermia reduces cerebral oxygen requirements, allowing prolonged time of circulatory collapse before brain damage occurs. (Ann Surg 1982;195:492; http://bit.ly/2xqGTpF.)
Hypothermia can cause ECG changes, including prolonged PR and QRS intervals and the distinctive Osborn wave. (Lancet 1961;2:1213.) Ventricular fibrillation is a risk at temperatures below 32°C, and can result from hypoxia, hypovolemia, and mechanical jostling. (N Engl J Med 1994;331:1756.)
Hypothermia causes decreased tissue oxygenation due to a left shift of the oxyhemoglobin-dissociation curve. Vasoconstriction, increased blood viscosity, and ventilation-perfusion mismatch also contribute to decreased oxygenation, which leads to elevated lactate and metabolic acidosis. Hypothermia also leads to coagulopathy and decreased platelet activity. (N Engl J Med 1994;331:1756.)
Prehospital management of hypothermia should involve removing the patient from cold exposure, drying the patient, and covering him with insulation, a vapor barrier, and ideally a heat source. Warming techniques include heat packs or hot water bags applied to the axilla, chest, or back. (Injury 2018;49:149.)
Rewarming strategies can be passive or active. Active external rewarming techniques include immersion, radiant heat, air, and heating blankets. External rewarming can cause peripheral vasodilation, which then results in core temperature drop called the afterdrop. Active core rewarming techniques include heated humidified air, which raises core temperature by 1-2°C per hour. Warm intravenous fluids also have an added benefit of volume repletion.
Peritoneal lavage raises the core temperature by 2-4°C per hour. Pleural lavage is another option that transfers heat directly to the mediastinum. Continuous venovenous rewarming can raise the core temperature by approximately 2°C per hour. Extracorporeal rewarming is the most efficient method, raising the core temperature by 1-2°C every three to five minutes. (N Engl J Med 1994;331:1756.) Contraindications to cardiopulmonary bypass for hypothermia include asphyxia, severe traumatic injury, and serum potassium level higher than 10 mmol/L. (N Engl J Med 1997;337:1500.)
Serum potassium is the main prognostic indicator utilized in triage for hypothermic cardiac arrest in the decision to initiate extracorporeal rewarming. Initial hypothermic hypokalemia is linked to intracellular shift. Subsequently, late hypothermic cardiac arrest can cause hyperkalemia secondary to cell lysis. A potassium cutoff of 8 mmol/L can be used in the decision to initiate extracorporeal rewarming, and can be used in austere settings to terminate resuscitation in the field. Other factors include elevated lactate, low pH, and coagulopathy. No specific thresholds, however, have been validated. (Resuscitation 2017;118:35.)
Trauma activation was called to ready the OR and an AV rewarming catheter was placed in our patient. He was transferred promptly to the OR for cardiac bypass and rewarming and later to rehab after his postoperative ICU course.
Hypothermia should not be a forgotten “H” in the ACLS guidelines for cardiac arrest. The case presented in this article highlights the reversibility of hypothermia and cardiac arrest. The American Heart Association's 2015 hypothermia guidelines state that “patients should not be considered dead before warming has been provided” (http://bit.ly/2xqCovn), echoing the common emergency medicine mantra that a patient is not dead until he is warm and dead. Physicians should be aware of potential environment factors that can contribute to a patient's emergency department presentation. It was life-saving for our patient.
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