Rewarming is the initial, imperative treatment for all hypothermic patients. Resuscitation begins with rapid assessment and support of airway, breathing, and circulation, simultaneously with the initiation of rewarming, and prevention of further heat loss. All cold, wet clothing must be removed and replaced with warm, dry clothing and blankets. Further rewarming methods are determined by the degree of hypothermia and available resources.
Mild or stage I hypothermia can be treated with passive external rewarming (eg, removing and replacing wet clothes with dry ones) or by active external rewarming. In contrast to those with more severe hypothermia, it is safe and recommended for the uninjured patient with mild hypothermia to become physically active to generate heat. This increases internal heat production through shivering and increased metabolism. Active external rewarming is noninvasive, highly effective, and safe for mild hypothermia. It involves applying external heat to the patient’s skin. Examples include warm bedding, heated blankets, heat packs, and immersion into a 40°C bath. Warm bath immersion limits the ability to monitor the patient or treat other coexisting conditions. Patients with mild hypothermia and previous good health usually respond well to passive and active external warming.
Stage II and III hypothermia are treated as above with the addition of more aggressive rewarming strategies. This requires close monitoring of vital signs and cardiac rhythm during rewarming. Warm intravenous fluids (38–42°C) are considered minimally invasive and effective. Warm parenteral fluids are preferred over more invasive methods such as thoracic lavage, peritoneal lavage, and endovascular devices that may increase the risk of coagulopathy and thrombosis.
As hypothermia becomes more severe, there are increased complications of both hypothermia itself and of rewarming. Complications of rewarming occur as colder peripheral blood returns to central circulation. This may result in core temperature afterdrop, rewarming lactic acidosis from shunting lactate into the circulation, rewarming shock from peripheral vasodilation, and hypovolemia, ventricular fibrillation, and other cardiac arrhythmias. Afterdrop can be lessened by active external rewarming of the trunk but not the extremities and by avoiding any muscle movement by the patient. There is some evidence to suggest that head warming is a viable alternative to increase core body temperature if torso warming in contraindicated (eg, when performing cardiopulmonary resuscitation). Extreme caution must be taken when handling the hypothermic patient to avoid triggering potentially fatal arrhythmias in a phenomenon known as rescue collapse.
Patients with hemodynamic instability or cardiac arrest should be transferred to a facility with ECMO or cardiopulmonary bypass capability. There is no established definition in the United States regarding the criteria for what qualifies as sufficiently unstable to warrant ECMO or bypass in this situation.
Early recognition and advanced management guidelines are needed for patients with stage IV hypothermia. For hypothermic patients in cardiac arrest, high-quality CPR must be initiated and continued until the patient’s core body temperature is at least 32°C. Below 30°C, arrhythmias and asystole may be refractory to drug therapy until the patient has been rewarmed; therefore, treatment should focus on excellent CPR technique in conjunction with aggressive rewarming of the patient. Epinephrine or vasopressin may be given in cardiac arrest of the severely hypothermic patient. The European Resuscitation Council recommends withholding epinephrine until warmed to 30°C, and decreasing the frequency of administration with temperatures of 30°C to 35°C. The American Heart Association permits dosage as usual in conjunction with rewarming. International Commission for Mountain Emergency Medicine recommends extracorporeal life support as the treatment of choice for patients at high risk for hypothermic cardiac arrest. Extracorporeal life support has been shown to substantially improve survival of patients with unstable circulation or cardiac arrest.
Any hypothermic patient with return of spontaneous circulation must be monitored very closely because of the high likelihood of subsequent multiorgan system failure. Patients who are in cardiac arrest after a drowning or an avalanche have a worse prognosis because they are more likely to have experienced asphyxia and associated injuries in addition to hypothermia.