Mild hypothermia is defined as a core body temperature of 32°C to 35°C (89.6°F to 95°F). [1-2] It is an environmental emergency responsible for approximately 1,300 deaths annually in the United States, with the highest mortality among men, the elderly, and rural populations. [3] Patients with mild hypothermia retain consciousness, shivering, and a perfusing rhythm, but movement and coordination are impaired. [4]
1. History
- Duration and nature of cold exposure (environmental, water immersion, indoor)
- Onset: gradual vs. sudden (e.g., cold water immersion)
- Ability to self-extricate or seek shelter
- Wet clothing, wind exposure, ground contact
- Alcohol or substance use prior to or during exposure
- Caloric intake and hydration status — energy depletion accelerates cooling [5]
- Associated trauma (falls, avalanche, drowning)
- Underlying medical conditions that impair thermoregulation (hypothyroidism, adrenal insufficiency, diabetes, spinal cord injury) [2][5]
- Medication changes (especially recent antipsychotic initiation or dose increase) [6]
2. Alarm Features
Red flags suggesting progression to moderate/severe hypothermia or life-threatening pathology:
- Decreased responsiveness, mumbling speech, confusion [3]
- Loss of or slowing shivering (suggests core temp approaching ≤32°C) [1][4]
- Cyanosis, pallor, frozen skin [3]
- Stumbling, inability to participate in own care [3]
- Systolic BP <90 mmHg or ventricular arrhythmias [1]
- Paradoxical undressing (typically <28°C) [5]
- Signs of secondary hypothermia (e.g., myxedema coma features: altered mental status + bradycardia in a non-exposure setting) [7]
3. Medications
Medications that contribute to hypothermia risk
- Antipsychotics (highest risk): olanzapine, risperidone, clozapine, ziprasidone — risk is greatest in the first 7–10 days of initiation or dose increase [6][8-9]
- Benzodiazepines and sedatives [10]
- Beta-blockers (impair thermogenic response) [10]
- General anesthetics (expand the interthreshold range, making patients poikilothermic) [11]
- Opioids
- Ethanol (vasodilation + impaired judgment)
Medications to avoid in hypothermia
- QT-prolonging drugs should be avoided, as hypothermia itself prolongs QT [12]
- Drug clearance is reduced during hypothermia — dose adjustments may be needed for drugs with narrow therapeutic indices [13]
No specific pharmacologic treatment is indicated for mild hypothermia; management is rewarming-focused. [1][4]
4. Diet
- Warmed, high-calorie liquids and food should be given to alert patients with intact swallow and no aspiration risk [3-4]
- Shivering increases metabolic rate ~5–6× baseline, making caloric support essential to sustain endogenous heat production [3]
- Avoid alcohol (causes vasodilation and further heat loss)
- Ensure adequate hydration — cold-induced diuresis contributes to volume depletion [14]
5. Review of Systems
- Neuro: confusion, irritability, poor judgment, incoordination (brain activity declines ~33–34°C) [14]
- Cardiac: palpitations, chest pain
- Pulmonary: dyspnea, cough (aspiration risk)
- GI: nausea (decreased motility begins ≤35°C) [15]
- GU: urinary urgency (cold diuresis) [1]
- MSK: shivering, muscle stiffness, weakness
- Skin: cold extremities, color changes, frostbite assessment
- Endocrine: symptoms of hypothyroidism, adrenal insufficiency
6. Collateral History and Family History
- Witnesses to exposure duration and circumstances
- Baseline mental status and functional capacity
- Psychiatric history (schizophrenia patients on antipsychotics at higher risk) [9-10]
- Housing status — homelessness is a major risk factor [2][4]
- Family history of endocrine disorders (hypothyroidism, adrenal insufficiency)
- Social isolation, elder neglect, substance use history
7. Risk Factors
- Extremes of age (elderly and very young) [3]
- Alcohol and substance intoxication [2][4]
- Homelessness / inadequate shelter [2]
- Psychiatric illness (impaired self-care, antipsychotic use) [10]
- Endocrine disorders: hypothyroidism, hypoadrenalism, hypopituitarism [5][7]
- Malnutrition and energy depletion [5]
- Immobility, debilitation, spinal cord injury
- Water immersion (cooling rate 1.0–1.8°C/h in 10–16°C water) [1]
- Trauma
- Sepsis
- Children: higher body surface area-to-mass ratio, limited glycogen stores [16]
8. Differential Diagnosis
- Secondary hypothermia from underlying illness (myxedema coma, adrenal crisis, sepsis, hypoglycemia, stroke, DKA) [5][7]
- Drug/toxin-induced hypothermia (antipsychotics, sedatives, ethanol, opioid overdose) [6][17]
- Sepsis with hypothermia (especially in elderly — may present with low rather than high temperature)
- Hypoglycemia
- CNS pathology (stroke, traumatic brain injury affecting hypothalamic thermoregulation)
- Drowning / near-drowning
Key distinguishing point: Primary hypothermia occurs in otherwise healthy individuals overwhelmed by cold stress; secondary hypothermia occurs even in warm environments and mandates workup for the underlying cause. [5]
9. Past Medical History
- Prior hypothermia episodes
- Hypothyroidism, adrenal insufficiency, diabetes
- Cardiovascular disease (limits compensatory response)
- Psychiatric illness and current medications
- Substance use disorders
- Peripheral neuropathy (impaired cold perception)
- Prior frostbite or cold injury
- Surgical history (splenectomy, thyroidectomy)
10. Physical Exam
- Vitals: Core temperature measurement is essential — use esophageal thermometry (most accurate) or low-reading rectal thermometer; standard tympanic/oral thermometers may not read below 34°C. Expect tachycardia and tachypnea in mild hypothermia. [1-2]
- Neuro: Assess alertness (should be preserved in mild hypothermia), coordination (impaired), speech, judgment [4]
- Skin: Cold extremities, pallor, assess for frostbite; check skin under any active warming devices every 20–30 min for burns [4]
- Cardiac: Auscultate for irregular rhythm
- Musculoskeletal: Active shivering (present in mild; slows/stops in moderate) [4]
- Trauma survey: Assess for concomitant injuries
11. Lab Studies
- Point-of-care glucose — hypoglycemia is common and must be excluded [18]
- BMP/CMP — electrolyte disturbances (hypokalemia or hyperkalemia during rewarming), renal function [15]
- CBC — leukopenia may occur; assess for infection
- Coagulation studies — hypothermia impairs platelet function and coagulation cascade, but standard labs run at 37°C may appear falsely normal [19-20]
- Lactate — elevated from shivering and poor perfusion [18]
- TSH, cortisol — if secondary hypothermia suspected (especially in non-exposure settings) [7]
- Blood gas — may show respiratory alkalosis early (hyperventilation from shivering) or mixed acid-base disorder [21]
- Lipase, troponin — as clinically indicated
- Toxicology screen — if intoxication suspected [17]
12. Imaging
- Chest X-ray — if aspiration, pneumonia, or pulmonary edema suspected
- CT head — if altered mental status out of proportion to temperature, or concern for stroke/trauma
- Imaging is generally not required for straightforward mild hypothermia with clear environmental exposure and appropriate clinical response to rewarming
13. Special Tests
- Core temperature measurement: Esophageal probe is gold standard in clinical settings; epitympanic thermistors may be reliable if ear canal is clear and sealed [2]
- Swiss Staging System (revised): Clinical staging based on AVPU scale and vital signs — Stage 1 (HT I) = conscious, shivering = mild hypothermia [2]
- Peripheral temperature measurements (infrared ear, skin) are unreliable [2]
14. ECG
ECG should be obtained in all hypothermic patients presenting to the ED.
Findings in mild hypothermia
- Sinus tachycardia (early) transitioning to sinus bradycardia
- Osborn (J) waves — positive deflections at the QRS-ST junction; can be present even in mild hypothermia, though more prominent with increasing severity (observed in ~53% of hypothermic patients overall) [22-23]
- PR prolongation, QRS widening, QT prolongation [23]
- Atrial fibrillation may begin to appear near 32°C [5]
- Shivering artifact on baseline
Critical pearl: Osborn waves can mimic ST-elevation and lead to misdiagnosis of STEMI — always correlate with core temperature. [7][24]
The following figure demonstrates classic Osborn waves in hypothermia (Panel A) with complete resolution after rewarming (Panel B):
15. Assessment
- Mild hypothermia (32–35°C) is characterized by preserved consciousness, active shivering, and impaired coordination [1][4]
- Patients retain the ability to generate heat through shivering, which is the primary rewarming mechanism at this stage [3-4]
- The critical threshold is 32°C — below this, shivering diminishes, cardiac instability risk increases, and the patient transitions to moderate hypothermia requiring more aggressive intervention [5][14]
- Always consider secondary causes if the exposure history does not match the degree of hypothermia [5][7]
16. Treatment Plan
Initial stabilization
- Remove from cold environment; remove wet clothing only once in a warm/sheltered setting [3-4]
- Insulate from ground and elements with vapor barrier (plastic/foil) + dry insulating layers, especially head and neck [3-4]
- Handle gently (though dysrhythmia risk is low in mild hypothermia, gentle handling is good practice) [4]
Rewarming
- Passive external rewarming: Blankets, warm environment — allows endogenous heat production via shivering (rate ~0.1–0.36°C/h) [3]
- Active external rewarming (preferred, faster): Forced warm air blankets, chemical heat packs, or heating blankets applied to axillae, chest, and back (rate ~0.57–1.45°C/h) [3-4]
- Active external rewarming is more effective than body-to-body warming [3]
- Check skin under heat sources every 20–30 min to prevent burns [4]
Supportive care
- Warmed, high-calorie oral fluids/food if alert with intact swallow [4]
- IV warmed normal saline if IV access obtained
- Correct hypoglycemia
- Continuous cardiac monitoring during rewarming
- Patient should remain seated or horizontal for at least 30 min; gradual increase in activity thereafter [4]
No specific medications are indicated for mild hypothermia itself. Treat underlying causes (e.g., levothyroxine/hydrocortisone for myxedema coma). [7]
17. Disposition
Discharge criteria (mild hypothermia)
- Core temperature normalized (≥36°C)
- Alert, oriented, ambulatory
- Shivering resolved
- No underlying medical cause identified
- Safe, warm environment available for discharge
- Able to care for self or has adequate support
- In field settings with full recovery and mitigated risk factors, hospital transport may not be necessary [1]
Admission criteria
- Failure to rewarm or continued decline in temperature
- Moderate or severe hypothermia (core temp <32°C)
- Hemodynamic instability, dysrhythmia
- Suspected secondary hypothermia requiring workup
- Significant comorbidities, trauma, or intoxication
- Elderly, homeless, or unable to return to safe environment
Specialist consultation triggers
- Cardiology if dysrhythmia
- Endocrinology if myxedema coma or adrenal crisis suspected
- Toxicology if drug-induced hypothermia
- Critical care if progressing to moderate/severe hypothermia
18. Follow Up / Return Precautions
Follow-up
- Primary care follow-up within 48–72 hours if discharged
- Endocrine workup follow-up if secondary hypothermia suspected
- Medication review if drug-induced hypothermia is a concern (especially antipsychotics — consider dose adjustment or alternative agent) [6]
Return precautions — instruct patients to return immediately for:
- Recurrent shivering or feeling cold despite warm environment
- Confusion, drowsiness, slurred speech
- Chest pain, palpitations, irregular heartbeat
- Skin color changes (blue/gray), numbness, or signs of frostbite
- Inability to care for self
Patient counseling
- Dress in layers; keep dry; cover head and extremities
- Avoid alcohol in cold environments
- Ensure adequate caloric intake during cold exposure
- Elderly patients and caregivers should maintain adequate home heating
- Expected recovery: mild hypothermia typically resolves fully with rewarming over 1–4 hours without sequelae [1][4]
References
1. ACSM Expert Consensus Statement: Injury Prevention and Exercise Performance During Cold-Weather Exercise. — Castellani JW, Eglin CM, Ikäheimo TM, et al. Current Sports Medicine Reports. 2021.
2. Extracorporeal Life Support in Accidental Hypothermia. — Mendrala K, Podsiadlo P, Darocha T. The Journal of the American Medical Association. 2025.
3. 2024 American Heart Association and American Red Cross Guidelines for First Aid. — Hewett Brumberg EK, Douma MJ, Alibertis K, et al. Circulation. 2024.
4. Accidental Hypothermia: Guidelines from the Wilderness Medical Society. — American Academy of Family Physicians (2020). 2020.
5. Accidental Hypothermia. — Brown DJ, Brugger H, Boyd J, Paal P. The New England Journal of Medicine. 2012.
6. Hypothermia Due to Antipsychotic Medication: A Systematic Review. — Zonnenberg C, Bueno-de-Mesquita JM, Ramlal D, Blom JD. Frontiers in Psychiatry. 2017.
7. Electrocardiography Unmasking the Cause of Unexplained Coma. — Rajendran G, Mahalingam S, Ramkumar A. JAMA Internal Medicine. 2026.
8. The Risk Factors, Frequency and Diagnosis of Atypical Antipsychotic Drug-Induced Hypothermia: Practical Advice for Doctors. — Szota AM, Araszkiewicz AS. International Clinical Psychopharmacology. 2019.
9. Hypothermia Associated With Antipsychotic Drug Use: A Clinical Case Series and Review of Current Literature. — Kreuzer P, Landgrebe M, Wittmann M, et al. Journal of Clinical Pharmacology. 2012.
10. Risk Factors for Hypothermia in Psychiatric Patients. — Young DM. Annals of Clinical Psychiatry : Official Journal of the American Academy of Clinical Psychiatrists. 1996.
11. Mild Perioperative Hypothermia. — Sessler DI. The New England Journal of Medicine. 1997.
12. Hypothermia and Cardiac Electrophysiology: A Systematic Review of Clinical and Experimental Data. — Dietrichs ES, Tveita T, Smith G. Cardiovascular Research. 2019.
13. Effects of Hypothermia on Pharmacokinetics and Pharmacodynamics: A Systematic Review of Preclinical and Clinical Studies. — van den Broek MP, Groenendaal F, Egberts AC, Rademaker CM. Clinical Pharmacokinetics. 2010.
14. Wilderness Medical Society Clinical Practice Guidelines For the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. — Dow J, Giesbrecht GG, Danzl DF, et al. Wilderness & Environmental Medicine. 2019.
15. Hypothermia Therapy: Neurological and Cardiac Benefits. — Delhaye C, Mahmoudi M, Waksman R. Journal of the American College of Cardiology. 2012.
16. Part 10: Adult and Pediatric Special Circumstances of Resuscitation: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Cao D, Arens AM, Chow SL, et al. Circulation. 2025.
17. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. — Panchal AR, Bartos JA, Cabañas JG, et al. Circulation. 2020.
18. Metabolic Aspects of Hypothermia in the Elderly. — Stoner HB, Frayn KN, Little RA, et al. Clinical Science. 1980.
19. Perioperative Thermoregulation and Heat Balance. — Sessler DI. Lancet. 2016.
20. Hypothermia-Associated Coagulopathy: A Comparison of Viscoelastic Monitoring, Platelet Function, and Real Time Live Confocal Microscopy at Low Blood Temperatures, an Experimental Study. — Wallner B, Schenk B, Hermann M, et al. Frontiers in Physiology. 2020.
21. Acute Mild Hypothermia in Awake Unrestrained Rats Induces a Mixed Acid-Base Disorder. — Alfaro V, Palacios L. Journal of Applied Physiology. 1996.
22. Electrocardiographic Patterns of Accidental Hypothermia. — Okumura H, Okada N, Hamanaka K, et al. The American Journal of Emergency Medicine. 2025.
23. Hypothermia: Evaluation, Electrocardiographic Manifestations, and Management. — Aslam AF, Aslam AK, Vasavada BC, Khan IA. The American Journal of Medicine. 2006.
24. Update to Practice Standards for Electrocardiographic Monitoring in Hospital Settings: A Scientific Statement From the American Heart Association. — Sandau KE, Funk M, Auerbach A, et al. Circulation. 2017.
25. Osborn Waves of Hypothermia. — Patel A, Getsos J. The New England Journal of Medicine. 1994.