Guidelines Summary
Guidelines on the out-of-hospital evaluation and treatment of accidental hypothermia were released in November 2019 by the Wilderness Medical Society. [18]
Key factors that should guide hypothermia treatment are as follows:
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Level of consciousness
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Alertness
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Shivering intensity
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Physical performance
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Cardiovascular stability (assessed based on blood pressure and cardiac rhythm)
Core temperature
While core temperature is difficult to accurately obtain in the field, it can provide additional helpful information. Core temperature should not be the sole basis for treatment.
Esophageal temperature is the most accurate minimally invasive method of measuring core temperature. The probe should be inserted into the lower third of the esophagus.
In a patient whose airway has not been secured by a supraglottic airway or endotracheal intubation, or in a patient with a secured airway but where no esophageal probe is available, the recommended method for obtaining a core temperature is an epitympanic thermometer designed for field conditions, with an isolating ear cap.
Field rewarming
External rewarming in the field is useful in both shivering and nonshivering patients.
Exogenous (active) rewarming methods that provide significant external heat include large chemical heat pads, large electric heat pads or blankets, warm water bottles, and the Norwegian-designed charcoal-burning Heat Pac (ensure adequate ventilation, owing to carbon monoxide emissions).
In order to maximize the total body net heat gain achieved, active heating is more effective when combined with insulation and some sort of vapor barrier; this creates an effective hypothermia enclosure system.
To achieve the most effective rewarming, external heat should be concentrated on the axillae, chest, and back (in that order). These areas have the highest potential for conductive heat transfer.
Resuscitation
Cardiopulmonary resuscitation (CPR) and other resuscitation methods should be attempted unless contraindications exist. Important factors that do not constitute contraindications to resuscitation in a severely hypothermic patient include fixed, dilated pupils; apparent rigor mortis; and dependent lividity. Continue resuscitation attempts regardless of measured core temperature.
For a hypothermic patient in cardiac arrest, perform immediate, high-quality CPR. In situations where performing immediate and continuous CPR is impossible or deemed unsafe, perform delayed or intermittent CPR. In hypothermic patients in cardiac arrest, the chest compression delivery rate is the same as in normothermic patients.
If the automated external defibrillator (AED) device signals that a shock is advised, attempt defibrillation and start CPR. If the AED device signals that no shock is advised and otherwise the patient displays no carotid pulse (after palpating for at least 1 min) and no normal breathing or other signs of life, and ultrasound is not available to verify cardiac activity or pulse, start CPR.
Regarding airway management in resuscitation, the principles are the same in hypothermic patients as in normothermic patients. Additionally, the advantages of advanced airway management outweigh the risk of causing ventricular fibrillation.
Hypothermic patients should be resuscitated with normal saline warmed to 40-42°C (104-107.6°F) administered either intravenously or intraosseously. Use caution to avoid volume overload. If possible, administer fluids as boluses rather than by continuous infusion. The goal of fluid administration is maintaining systolic blood pressure at a level that provides adequate perfusion, depending on the degree of hypothermia.
Transfer
Patient conditions and transfer/care recommendations are as follows:
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Alert patient with mild hypothermia: Treat in the field
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Uninjured patient who is completely alert and shivering: Treat without transport to a hospital
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Patient not profoundly hypothermic or hemodynamically unstable: Transport to the nearest facility
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Profoundly hypothermic patient with witnessed cardiac arrest (regardless of return to spontaneous circulation in the field): Transfer to a center where extracorporeal life support can be initiated greatly improves chances of survival
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Patient with injuries meeting trauma criteria: Transport to a trauma center
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Osborne (J) waves (V3) in a patient with a rectal core temperature of 26.7°C (80.1°F). ECG courtesy of Heather Murphy-Lavoie of Charity Hospital, New Orleans.
