Hypothermia is treated by gradually raising the body’s core temperature, using methods that range from simply adding warm blankets to advanced hospital procedures that heat the blood directly. The right approach depends on how cold the person is. Mild hypothermia (core temperature between 32 and 35°C, or 90 to 95°F) can often be managed with passive rewarming, while moderate hypothermia (28 to 32°C, or 82 to 90°F) and severe hypothermia (below 28°C, or 82°F) require progressively more aggressive medical intervention.
Passive Rewarming for Mild Cases
The simplest form of treatment is passive rewarming, which means stopping the body from losing more heat and letting it generate warmth on its own. This works for mild hypothermia because the body’s shivering reflex is still functional and producing heat. The priority is removing wet clothing, moving the person to a warm environment, and covering them with insulating layers like blankets or sleeping bags. Covering the head is especially important since it’s a major source of heat loss.
Passive rewarming alone won’t work when core temperature drops below about 32°C (90°F). At that point, the body’s shivering mechanism starts to fail, and it can no longer generate enough heat to recover without outside help.
Active External Rewarming
When passive methods aren’t enough, active external rewarming applies heat directly to the body’s surface. This includes heated blankets, warm water bottles, chemical heat packs, heat lamps, and forced-air warming systems. Of these, forced-air systems are among the most widely used in hospitals. A well-known example is the Bair Hugger, which blows warm air through a blanket draped over the patient. These systems raise core temperature at a rate of roughly 1.0 to 2.5°C per hour while still allowing medical staff to monitor the patient and perform other treatments.
Heat packs and warm water bottles should be applied to the torso, particularly the chest, neck, armpits, and groin, where large blood vessels run close to the skin. A common mistake in first-aid situations is warming the arms and legs first. This can cause cold blood from the extremities to rush back toward the heart, potentially triggering a dangerous drop in blood pressure or cardiac rhythm problems.
Active Internal Rewarming
For moderate to severe hypothermia, warming from the outside isn’t fast enough. Active internal rewarming heats the body from within using several techniques, often in combination.
Warmed IV Fluids
Intravenous saline heated to body temperature or slightly above is one of the most accessible internal rewarming methods. Cold IV fluids would steal heat from the body, so warming them prevents further cooling and contributes a modest amount of heat. On its own, warmed IV fluid doesn’t raise core temperature dramatically, but it supports other rewarming efforts and helps restore blood volume.
Warmed Humidified Oxygen
Breathing in cold air cools the body from the inside with every breath. Delivering warmed, humidified oxygen (typically around 42°C) through a mask or breathing tube reverses this. In one study of post-surgical patients, those receiving warmed humidified oxygen rewarmed at 0.7°C per hour compared to 0.4°C per hour for those on standard oxygen. It’s a relatively gentle technique, but it adds up, especially when combined with other methods.
Body Cavity Lavage
In more severe cases, warm sterile fluid can be circulated through body cavities, including the chest and abdomen. This puts heated fluid in direct contact with internal organs, transferring heat more efficiently than surface warming alone. It’s an invasive procedure used when other rewarming methods are insufficient.
ECMO for Life-Threatening Cases
Severe hypothermia can cause the heart to stop. When a patient is in cardiac arrest from hypothermia, the most effective rescue option is extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass. Both work by drawing blood out of the body, warming it through a machine, and returning it to circulation. This approach can rewarm a patient at roughly 6 to 7°C per hour, far faster than any other method.
Experts strongly recommend these machines for hypothermic cardiac arrest, and outcomes can be surprisingly good. Because cold slows the brain’s oxygen demand, people have survived prolonged cardiac arrest from hypothermia with full neurological recovery, something that would be impossible at normal body temperature. Survival depends partly on blood chemistry. Extremely high potassium levels in the blood suggest that cells have been irreversibly damaged, and beyond a certain threshold, rewarming is unlikely to succeed.
Why “Afterdrop” Matters
One of the most counterintuitive aspects of hypothermia treatment is a phenomenon called afterdrop. Even after rewarming begins, a patient’s core temperature can continue to fall for a period before it starts to rise. This happens because heat moves slowly through tissue. The cold outer layers of the body act like a heat sink, drawing warmth away from the core even as external heat is applied.
For a long time, afterdrop was blamed on cold blood rushing back from the arms and legs to the heart. But research suggests blood flow to the extremities stays low until afterdrop is complete, making a simpler physical explanation more likely: heat just takes time to conduct through tissue. Regardless of the mechanism, afterdrop means that a patient who seems to be getting treatment may temporarily get colder before improving. This is normal and expected, but it’s one reason rewarming needs to be monitored carefully, especially in moderate and severe cases where even a small further drop could push the heart into a dangerous rhythm.
Cardiac Risks During Rewarming
A cold heart is an irritable heart. As core temperature drops below 32°C, the risk of abnormal heart rhythms climbs sharply. The heart can slip into ventricular fibrillation, a chaotic quivering that stops it from pumping blood. Below 28°C, even gentle physical handling of the patient can trigger this. That’s why rescuers are taught to move hypothermic patients slowly and carefully.
If the heart does go into a dangerous rhythm, defibrillation (delivering an electrical shock) is reasonable to attempt even at temperatures below 30°C, per European Resuscitation Council guidelines. However, a severely cold heart may not respond to defibrillation or cardiac medications the way a warm heart would. The general strategy is to attempt defibrillation, continue CPR, and focus on raising the core temperature. Once the heart warms up, it becomes far more responsive to standard resuscitation.
Rewarming in Newborns
Infants lose heat much faster than adults because of their high surface-area-to-body-weight ratio and limited ability to shiver. Rewarming a hypothermic newborn requires particular caution. Most neonatal units rewarm at a rate below 0.5°C per hour, a pace borrowed from protocols used in babies treated with therapeutic cooling after birth complications. That said, the optimal speed remains debated. One retrospective study found no significant association between rewarming rate and complications like low blood sugar, seizures, respiratory distress, or mortality. Official guidelines on the best pace are still lacking, so clinical teams tend to err on the side of gradual warming while closely monitoring the infant’s blood sugar and breathing.
What to Do Before Help Arrives
If you’re with someone who may be hypothermic, the most important steps are straightforward. Get them out of the cold and wind. Replace any wet clothing with dry layers. Wrap them in whatever insulation is available, including your own body heat if nothing else is at hand. Focus warmth on the torso, not the extremities. Give warm, sweet drinks if the person is fully conscious and able to swallow, but avoid alcohol, which dilates blood vessels and accelerates heat loss. Keep the person as still as possible to reduce the risk of triggering a heart rhythm problem. Do not rub or massage cold limbs.
If the person is unresponsive or not breathing, start CPR. A cold body slows all biological processes, meaning someone who appears dead from hypothermia may still be recoverable. The longstanding principle in emergency medicine: no one is dead until they are warm and dead.