# Hypothermia > Hypothermia for NEET-PG Medicine: staging, Osborn waves, rewarming strategies and arrhythmia risks that shape outcome in patients exposed to cold. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/hypothermia - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-08 - Last updated: 2026-10-08 - Reference basis: Tintinalli's Emergency Medicine; ERC Guidelines for Resuscitation; Harrison's Principles of Internal Medicine - How to cite: "Hypothermia", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/hypothermia ## Direct answer Hypothermia is a core temperature below 35 degrees Celsius, and its most dangerous effect is arrhythmia, particularly ventricular fibrillation once cooling passes about 30 degrees. The characteristic ECG finding is the Osborn wave, a positive deflection at the J point that grows as temperature falls and disappears on rewarming. Management rests on gentle handling, severity-matched rewarming and persistent resuscitation, since cold patients can survive arrests that would otherwise be fatal. ## What you must remember - **Severity staging:** Mild hypothermia is 32 to 35 degrees with shivering; moderate is 28 to 32 degrees with shivering lost and confusion; severe is below 28 degrees with no shivering. - **Osborn wave:** A J-point deflection, most prominent below about 32 degrees; it is nonspecific and does not by itself indicate ischaemia. - **Arrhythmia pattern:** Atrial fibrillation and bradycardia are common in mild to moderate cooling, while ventricular fibrillation and asystole dominate below about 30 degrees. - **Gentle handling:** Rough movement of a cold heart can trigger ventricular fibrillation, so the patient should be moved horizontally and kept as still as possible. - **Passive and active rewarming:** Insulation and warm environment suffice for mild cases, while forced-air warming and warmed intravenous fluids at about 40 to 42 degrees help moderate cases. - **Afterdrop:** Rewarming cold limbs in severe cases returns cold blood to the core and lowers core temperature further, so central rewarming is preferred. - **Extracorporeal rewarming:** Reserved for severe cases, arrest, or failure of conventional rewarming. ## A cold-room presentation and a rewarming plan A 68-year-old man is found drowsy on a cold floor in an unheated room on a north Indian winter night, after a day of drinking. His heart rate is 38 per minute, and the ECG shows atrial fibrillation with Osborn waves. 1. **Measure the core:** Standard clinical thermometers may not register below about 34 degrees, so a low-range core probe is used, and it reads 30 degrees. 2. **Handle gently and stabilise:** The first steps are gentle handling, removal of wet clothing, insulation and a horizontal position. Glucose is measured, because hypoglycaemia is a hidden cause. 3. **Search for precipitants:** Cortisol, thyroid function, electrolytes and cultures are sent, since hypothyroidism, adrenal insufficiency and sepsis are classic precipitants. 4. **Rewarm from the core:** Warmed fluids and humidified warm oxygen follow, with active external warming to the trunk preferred over limb rewarming. 5. **Prepare for fibrillation:** A defibrillator stays ready, because deterioration towards ventricular fibrillation is the main danger at this temperature. 6. **Space the drugs:** Drug clearance slows in the cold, so repeat doses of vasoactive or antiarrhythmic drugs are spaced out and reviewed as the temperature rises. 7. **Escalate if rewarming stalls:** If the rhythm worsens or rewarming stalls, extracorporeal rewarming becomes the next step. ## Where hypothermia questions go wrong The traps cluster around the J wave, shivering and the saying about death. - **Trap:** attributing every J wave to hypothermia. — **Correct:** J waves also appear in hypercalcaemia and after some brain injuries, so the diagnosis rests on the clinical setting together with a low core temperature. - **Trap:** reading shivering as a sign of improvement. — **Correct:** shivering disappears below roughly 30 degrees, so a patient who has stopped shivering is more deeply hypothermic, not recovering. - **Trap:** stopping resuscitation early after cold immersion or exposure. — **Correct:** the saying not dead until warm and dead tests whether the candidate continues resuscitation far longer than usual. - **Trap:** avoiding limb rewarming in every case. — **Correct:** the danger is afterdrop in severe cases, which is a reason for central rewarming, not a rule against warming the periphery in mild cases. ## Frequently asked questions ### What is the characteristic ECG finding in hypothermia? Osborn waves, which are positive deflections at the J point, are the characteristic ECG finding of hypothermia. They become more prominent as core temperature falls below about 32 degrees and resolve with rewarming, so they reflect the degree of cooling rather than ischaemia. ### At what core temperature does ventricular fibrillation risk rise in hypothermia? Ventricular fibrillation and asystole become the dominant arrhythmias when core temperature falls below about 30 degrees Celsius, and spontaneous arrhythmia risk climbs as cooling deepens. Handling should therefore be gentle, because rough movement can trigger fibrillation in a cold myocardium. ### Why is limb rewarming avoided in severe hypothermia? Rewarming cold limbs in severe hypothermia returns cold peripheral blood to the core, causing a further fall in core temperature known as afterdrop. That can precipitate ventricular fibrillation, so rewarming should be central, using warmed fluids and extracorporeal support when needed. ### Why is resuscitation continued for longer in hypothermic arrest? Cold slows metabolism and protects the brain, so patients can survive prolonged arrest with good neurological outcomes. Resuscitation continues until the core is near normal, which is why the saying not dead until warm and dead is taught to every trainee. ### Which investigations look for a hidden cause of hypothermia? Blood glucose, thyroid function, cortisol, electrolytes, lactate and cultures should be checked in every hypothermic patient. Hypothyroidism, hypoglycaemia, sepsis, adrenal insufficiency and sedative drugs are the commonest hidden causes that examiners expect candidates to name.