baths is also possible but complicates monitoring or response to arrhythmias These methods, however, cause early warming of the skin and extremities with peripheral vasodilation and shunting of cold, acidemic blood to the core This causes the well-known phenomenon of “afterdrop” of core temperature Severe hypotension may also occur in chronic cases as vasodilation increases the effective vascular space External rewarming techniques limited to the head and trunk may minimize vasodilation and afterdrop In acute hypothermia, active external rewarming is appropriate, but there is some evidence that in chronic cases (more than 24 hours), mortality is higher if active external rewarming is used instead of simple passive techniques Core rewarming techniques are almost certainly more rapid and less likely to be associated with afterdrop, dangerous arrhythmias, or significant hypotension These methods are especially valuable in the setting of severe chronic hypothermia (temperature less than 32°C [89.6°F]), where fluid shifts are most likely to occur A nonshivering model of severe hypothermia indicated that inhalation rewarming offered no rewarming advantage, whereas forced air warming (approximately 200 W) allowed a 6- to 10-fold increase in rewarming rate over controls At the same time, peritoneal dialysis with dialysate warmed to 43°C (109.4°F) is effective and requires only equipment routinely available in most hospitals Gastric or colonic irrigation has also been advocated, but placement of the intragastric balloon may precipitate dysrhythmias Hemodialysis, extracorporeal blood rewarming, and mediastinal irrigation are effective but require mobilization of sophisticated equipment and personnel New endovascular warming catheters, introduced after cannulization of the femoral vein and advancement to the inferior vena cava, use closed-loop circuitry to maintain the patient’s temperature Indications for Admission and Discharge In patients with mild temperature depression (greater than 32°C [89.6°F]), external rewarming techniques and supportive care based on vital signs, ABGs, and metabolic parameters such as glucose and calcium levels, should result in prompt recovery Patients with mild hypothermia due to environmental exposure who improve with passive rewarming may be discharged after observation in the ED However, it should be noted that other causes of hypothermia should be ruled out prior to discharge Children who present with a temperature less than 32°C (89.6°F), and especially those in whom hypothermia developed over 24 hours or more, require meticulous attention to continuously changing vital signs and metabolic needs More elaborate core rewarming techniques are appropriate