# Hypothermia

Hypothermia requires core-temperature confirmation, recognition of temperature-dependent cardiovascular and neurologic depression, gentle handling, prevention of further heat loss, and escalation of rewarming support according to severity and circulatory status.

**Clinical question:** How should clinicians recognize, risk-stratify, and manage accidental hypothermia while distinguishing it from controlled temperature management?

Updated: 2026-08-21T01:34:22.431371+00:00

## What matters in practice
- Diagnose hypothermia with a core temperature below 35°C (95°F); use a low-reading thermometer when clinically suspected. [16][22]
- Progressive cooling causes impaired cognition, lethargy, declining consciousness, bradycardia, weak pulses, shallow respirations, and increasing risk of arrhythmia or cardiorespiratory arrest at lower temperatures. [22]
- Severe hypothermia below 30°C is associated with marked depression of cerebral blood flow and oxygen requirements. [3]
- Handle severely hypothermic patients cautiously and prioritize insulation, prevention of additional heat loss, core-temperature measurement, and rewarming appropriate to physiologic instability; detailed modality selection is not supported by the supplied excerpts. [12][21]
- Post-cardiac-arrest temperature control is distinct from accidental hypothermia management; contemporary guidance cited in the available literature supports temperature control within 32°C to 37.5°C, while the optimal target remains debated. [2][7]

## Confirm core hypothermia and assess physiologic severity

Temperature alone is important, but mental status and circulatory stability determine urgency.

Hypothermia is diagnosed by a core body temperature below 35°C (95°F). Surface or routine thermometers may be inadequate at low temperatures; suspected hypothermia warrants measurement with a low-reading device capable of assessing deep body temperature. [16][21][22]

Clinical severity tracks imperfectly with a single temperature measurement because environmental exposure, comorbidity, duration of cooling, trauma, intoxication, and measurement limitations may modify presentation. In early hypothermia, patients may remain alert and shiver. With progressive cooling, cognition deteriorates, lethargy and reduced interest in self-protection develop, and paradoxical undressing may occur. At lower temperatures, rigidity, slowed or absent respirations, weak pulses, hypotension, arrhythmias, and apparent absence of cardiorespiratory activity can occur. [22]

A core temperature below 30°C defines severe hypothermia in the cited resuscitation literature and is associated with substantial suppression of cerebral blood flow and cerebral oxygen requirement. This physiology can complicate bedside assessment and supports cautious interpretation of absent or profoundly reduced vital signs. [3]
- Obtain a core temperature early when cold exposure, altered mental status, bradycardia, unexplained hypotension, or apparent death follows environmental exposure. [16][21][22]
- Assess and document consciousness, shivering, respiratory effort, pulse quality, blood pressure, ECG rhythm, exposure history, trauma, immersion or avalanche context, and concurrent illness or intoxication; the available evidence excerpts do not provide a validated diagnostic scoring system. [12][17][22]
- Treat tremor artifact as a potential confounder during ECG interpretation in acute hypothermia. [14]

*Temperature-associated findings described in supplied clinical sources; findings overlap and should not replace direct physiologic assessment. [3][22]*

| Core temperature | Typical clinical implications | Immediate interpretation |
| --- | --- | --- |
| 32-35°C (90-95°F) | Often alert with shivering; mental performance may decline. [22] | Confirm core temperature, stop further cooling, monitor for deterioration. [16][22] |
| Near 29°C (85°F) | Lethargy and reduced engagement in self-protection may develop; consciousness declines. [22] | Escalate monitoring and rewarming support according to clinical instability. [12][22] |
| Below 30°C (86°F) | Severe hypothermia; cerebral blood flow and oxygen requirement are markedly depressed. [3] | Interpret profoundly depressed neurologic and cardiovascular function cautiously. [3][16] |
| Below 27°C (80°F) | Vital signs may become very slow or absent; arrhythmias and cardiorespiratory arrest may occur. [22] | Manage as a high-acuity resuscitation problem with continuous reassessment. [12][22] |

## Stabilize, prevent additional cooling, and plan rewarming

Management priorities depend on circulation, mental status, and severity rather than temperature alone.

The available Wilderness Medical Society guideline excerpts describe a structured approach to out-of-hospital evaluation and treatment of accidental hypothermia, but the supplied evidence does not provide sufficient detail to specify exact rewarming rates, fluid temperatures, extracorporeal criteria, or drug dosing. [1][12]

For the unstable or severely hypothermic patient, minimize unnecessary movement while completing airway, breathing, and circulation assessment. Hypothermia may produce profound bradycardia and low cardiac output; at moderate cooling, reduced metabolic demand may preserve supply-demand balance, whereas deeper hypothermia at or below 30°C carries greater arrhythmic risk. [20]

Avoid anchoring on environmental exposure alone. Hypothermia can coexist with trauma, hemorrhage, infection, endocrine disease, intoxication, metabolic derangement, or primary cardiac events. The supplied search results support broad evaluation but do not provide a source-supported laboratory or imaging bundle.
- Remove the patient from the cold environment, protect from further heat loss, and use continuous core-temperature monitoring when available. [12][21]
- Use continuous cardiac monitoring in clinically significant hypothermia because rhythm disturbances may occur as temperature falls. [20][22]
- For apparent cardiac arrest after prolonged exposure, do not rely solely on an initial impression of absent vital signs; profound hypothermia can markedly suppress cardiopulmonary activity. [3][16][22]
- Choose rewarming method and disposition according to core temperature, hemodynamic status, consciousness, associated injury or illness, and local critical care or extracorporeal support capability; exact selection criteria are not available in the supplied excerpts. [12]

### Cardiovascular and medication considerations

Hypothermia-related bradycardia lowers cardiac output, but metabolic rate also falls; the cited critical care review states that myocardial contractility and hypotension are not necessarily worsened by moderate hypothermia when hypovolemia is corrected. [20]

Cooling may impair insulin sensitivity, drug clearance, and coagulation. Anticipate altered pharmacokinetics and monitor glucose and bleeding risk when clinically relevant, particularly during prolonged controlled cooling. The supplied sources do not support drug-specific dosing adjustments for accidental hypothermia. [20]
- Do not infer that bradycardia alone requires treatment without considering temperature, perfusion, and concurrent hypovolemia. [20]
- Use ECG findings cautiously when shivering creates tremor artifact. [14]

*High-value bedside priorities for suspected accidental hypothermia. [12][16][20][21][22]*

| Decision point | Action | Reason |
| --- | --- | --- |
| Temperature measurement | Measure deep or core temperature with a low-reading device when possible. [16][21] | Routine devices may fail to identify clinically important low temperatures. [16] |
| Further heat loss | Immediately insulate and remove the patient from the cold environment. [12][22] | Ongoing exposure worsens neurologic and cardiovascular depression. [22] |
| Rhythm assessment | Use continuous cardiac monitoring for clinically significant hypothermia. [20][22] | Arrhythmias may emerge with progressive cooling. [20][22] |
| Hemodynamic instability | Assess volume status and correct hypovolemia when present while planning rewarming escalation. [20] | Moderate hypothermia may be tolerated better when hypovolemia is corrected. [20] |
| Apparent absence of vital signs | Escalate resuscitation evaluation rather than assuming irreversible death from examination alone. [3][16][22] | Profound cooling can markedly suppress cerebral and cardiopulmonary activity. [3][22] |

## Interpret ECG and physiologic changes in temperature context

Temperature can alter rhythm, hemodynamics, and monitoring reliability.

Acute hypothermia can produce ECG changes, and shivering-related tremor artifact is specifically described as a common ECG feature. Verify questionable tracings clinically and repeat acquisition after reducing artifact when feasible. [14]

At moderate therapeutic hypothermia, bradycardia commonly reduces cardiac output, but the associated reduction in metabolic demand may maintain or improve oxygen supply-demand balance. In contrast, deep hypothermia at or below 30°C is associated with more substantial physiologic suppression and increased arrhythmic concern. [20]

Monitor temperature trend, rhythm, hemodynamics, consciousness, respiratory status, glucose, and clinical evidence of bleeding or impaired drug handling during prolonged cooling or rewarming. Insulin resistance, impaired drug clearance, and mild coagulopathy are reported physiologic effects of hypothermia. [20]
- Do not equate a slow heart rate with isolated primary conduction disease until temperature and exposure history have been assessed. [20][22]
- Expect neurologic examination to be temperature-dependent; depressed consciousness in severe hypothermia should be reassessed during rewarming. [3][22]
- If using temperature-control devices, monitor both target achievement and the rewarming phase because device approaches differ in cooling speed, precision, and rewarming control. [24]

*Physiologic effects relevant to monitoring during hypothermia. [3][14][20][22]*

| System | Observed effect | Clinical consequence |
| --- | --- | --- |
| Neurologic | Marked depression of cerebral blood flow and oxygen requirement in severe hypothermia below 30°C. [3] | Avoid premature neurologic prognostication based on a cold examination alone. [3][16] |
| Cardiovascular | Bradycardia lowers cardiac output; deep hypothermia increases arrhythmic concern. [20] | Interpret rate and perfusion together; correct hypovolemia when present. [20] |
| Electrocardiographic | Shivering can cause tremor artifact. [14] | Confirm apparent rhythm abnormalities with repeat or artifact-reduced tracing. [14] |
| Metabolic and pharmacologic | Insulin resistance and impaired drug clearance may occur. [20] | Increase vigilance for glycemic disturbance and altered medication effect. [20] |
| Hemostatic | Mild coagulopathy may occur. [20] | Assess bleeding risk and interpret coagulation abnormalities in clinical context. [20] |

## Separate accidental hypothermia from post-arrest temperature control

Induced temperature management has different indications, targets, and monitoring goals.

Targeted temperature management, also termed therapeutic hypothermia in some literature, is a controlled intervention used within broader post-cardiac-arrest care rather than a treatment model for all cold-exposed patients. Earlier post-resuscitation guidance cited targets of 33°C to 36°C, while more recent literature describes guideline-supported temperature control between 32°C and 37.5°C. [7][24]

The optimal post-arrest temperature target remains debated. The available sources support careful temperature control and avoidance of uncontrolled fever but do not provide enough detail to recommend a specific target, duration, sedation regimen, neuromuscular blockade strategy, or rewarming rate for an individual patient. [2][7][24]

Cooling method affects speed of induction, precision of temperature control, and rewarming control. Endovascular systems may cool faster than other available methods in comparisons cited by ACEP, but the supplied excerpt does not establish superiority for patient-centered outcomes or define a preferred device for U.S. practice. [24]
- Do not apply post-arrest temperature targets to accidental hypothermia without considering whether the patient requires rewarming rather than controlled maintenance of a low temperature. [7][12][24]
- For comatose post-cardiac-arrest patients, integrate temperature control into comprehensive critical care rather than treating it as an isolated intervention. [2][24]
- Anticipate glucose dysregulation, reduced drug clearance, and coagulation effects during sustained induced hypothermia. [20]

*Accidental hypothermia and controlled post-arrest temperature management serve different clinical purposes. [7][12][20][24]*

| Feature | Accidental hypothermia | Post-arrest temperature control |
| --- | --- | --- |
| Clinical objective | Prevent further cooling and restore physiologic stability through appropriate rewarming. [12][22] | Deliver controlled temperature management as part of post-cardiac-arrest critical care. [2][24] |
| Temperature context | Core temperature is pathologically low, generally below 35°C. [16][22] | Published targets in supplied sources range from 32°C to 37.5°C; the optimal target remains debated. [7][24] |
| Device considerations | The supplied excerpts do not specify a preferred rewarming device or technique. [12] | Methods differ in cooling speed, precision, and control of rewarming. [24] |
| Monitoring concerns | Rhythm instability, depressed consciousness, respiratory compromise, and exposure-related comorbidity require reassessment. [20][22] | Monitor for insulin resistance, impaired drug clearance, and coagulopathy during cooling. [20] |

## Common questions

### What temperature defines hypothermia?

Hypothermia is defined as a core body temperature below 35°C (95°F). In suspected cases, use a low-reading device capable of measuring deep or core temperature. [16][21][22]

### When is hypothermia considered severe?

The cited resuscitation literature defines severe hypothermia as a core temperature below 30°C (86°F), a range associated with marked depression of cerebral blood flow and oxygen requirement. [3]

### Can a severely hypothermic patient appear pulseless or dead?

Yes. At very low temperatures, pulse and respirations may become extremely slow, weak, or apparently absent, and cardiorespiratory arrest may occur. Profound physiologic suppression warrants cautious assessment and resuscitation evaluation. [3][16][22]

### How should shivering affect ECG interpretation?

Shivering can generate tremor artifact on the ECG. Correlate with the patient and repeat or optimize the tracing when artifact may be mimicking a rhythm abnormality. [14]

### Is targeted temperature management the same as treating accidental hypothermia?

No. Accidental hypothermia requires prevention of further heat loss and rewarming based on severity and stability, whereas post-arrest temperature control is a deliberate ICU intervention with controlled targets and rewarming. [7][12][24]

## References
1. Part 10: Adult and Pediatric Special Circumstances of ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIR.0000000000001380
2. Part 11: Post–Cardiac Arrest Care: 2025 ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/CIR.0000000000001375
3. Part 8: Advanced Challenges in Resuscitation | Circulation — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/circ.102.suppl_1.i-229
4. Hypothermia and heart rate variability in a healthy newborn ... — www.nature.com — https://www.nature.com/articles/s41598-022-22426-3
5. Intraoperative accidental hypothermia as a probable cause ... — www.cell.com — https://www.cell.com/heliyon/fulltext/S2405-8440(23)06214-X
6. Systematic review of terminology, definitions, and eligibility criteria in trials of neonatal encephalopathy, hypoxic-ischemic encephalopathy, and perinatal asphyxia | Pediatric Research — www.nature.com — https://www.nature.com/articles/s41390-025-04750-2
7. Targeted temperature management alleviates post-resuscitation myocardial dysfunction by inhibiting ferroptosis — www.nature.com — https://www.nature.com/articles/s41420-025-02356-5
8. Glibenclamide Is Comparable to Target Temperature ... — www.ahajournals.org — https://www.ahajournals.org/doi/10.1161/JAHA.116.003465
9. Review Anti-arrhythmic and vasopressor medications for ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S030095720800110X
10. Characteristics and outcome of patients with hypothermic ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0300957217305968
11. Application of normothermic cardiac arrest algorithms to ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0300957205004600
12. Wilderness Medical Society Practice Guidelines for the Out ... — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S1080603214003263
13. Abstracts for the 2022 Scandinavian Society of ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/full/10.1111/aas.14218
14. Changes in electrocardiogram parameters during acute ... — physoc.onlinelibrary.wiley.com — https://physoc.onlinelibrary.wiley.com/doi/10.14814/phy2.14718
15. Hypothermia and targeted temperature management in ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/10.1111/vec.12572
16. Thermoregulatory Failure in the Elderly - Wongsurawat - 1990 — agsjournals.onlinelibrary.wiley.com — https://agsjournals.onlinelibrary.wiley.com/doi/10.1111/j.1532-5415.1990.tb05708.x
17. Accidental hypothermia in recreational activities in the ... — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/full/10.1111/sms.13294
18. Application of high-quality targeted temperature ... — journals.lww.com — https://journals.lww.com/md-journal/fulltext/2024/12200/application_of_high_quality_targeted_temperature.8.aspx
19. Therapeutic Hypothermia in the Postresuscitation Patient — journals.lww.com — https://journals.lww.com/aenjournal/_layouts/15/oaks.journals/downloadpdf.aspx?an=01261775-200810000-00006
20. Mechanisms of action, physiological effects, and... : Critical Care Medicine — journals.lww.com — https://journals.lww.com/ccmjournal/fulltext/10.1097/ccm.0b013e3181aa5241~mechanisms-of-action-physiological-effects-and-complications
21. Accidental Hypothermia: Peritoneal Dialysis — www.annemergmed.com — https://www.annemergmed.com/article/S0361-1124(77)80428-0/pdf
22. Considerations During Cold Weather Ops for LEO and TMPs | Tactical and Law Enforcement Medicine — www.acep.org — https://www.acep.org/talem/newsroom/january-2022/considerations-during-cold-weather-ops-for-leo-and-tmps
23. Cooling to Prevent Radiocontrast Nephropathy - American College of Cardiology — www.acc.org — https://www.acc.org/latest-in-cardiology/clinical-trials/2011/06/27/13/39/cool-rcn
24. Induced Hypothermia after Cardiac Arrest – Does the Method Matter? | Critical Care Medicine Section — www.acep.org — https://www.acep.org/criticalcare/newsroom/newsroom-articles/jun2020/induced-hypothermia-after-cardiac-arrest--does-the-method-matter

## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.