Textbook of Urgent Care Medicine, Chapter 7, Heat and Cold Urgencies

Published on October 26, 2026

Original authors: Devon Lathrop and John Shufeldt

Originally published in 2014. Substantially updated and clinically reviewed in 2026 to reflect current evidence, guidelines, and urgent care practice.

The human body functions best within a specific, narrow temperature range. Thus, when it is exposed to temperature extremes, it is at risk for significant injury or even death. Clinicians in an urgent care center are in a position to prevent severe sequelae and sometimes obviate the need for a trip to an emergency department. The first half of this chapter takes the clinician through diagnosis and treatment of heat urgencies, and the second half does the same for cold urgencies.

Heat Urgencies

Introduction

Heat illnesses result from one or more of the following: prolonged exposure to higher than normal temperatures, individual patient characteristics that decrease the body’s ability to cool, and inability to access cooler environments after exposure.

Heat illness is a spectrum that includes heat edema, heat syncope, exercise-associated muscle cramps, heat exhaustion, and heat stroke. Heat stroke is the critical diagnosis because organ injury is related to both the degree and duration of hyperthermia. The urgent care clinician should recognize it quickly, begin cooling immediately, and arrange emergency transfer without waiting for the diagnostic evaluation to be completed.

Presentation

• Heat stroke is a medical emergency characterized by central nervous system dysfunction in a patient with significant hyperthermia. A core temperature above 40°C (104°F) strongly supports the diagnosis, but treatment should not be delayed when heat stroke is clinically suspected and an accurate temperature is not yet available.
• Heat exhaustion can occur with prolonged exposure to higher-than-normal heat indexes and may cause weakness, fatigue, thirst, headache, nausea, dizziness, myalgias, tachycardia, and orthostatic symptoms without persistent central nervous system dysfunction.
• Heat syncope occurs when peripheral vasodilation, relative volume depletion, or both reduce cerebral perfusion.
• Heat cramps occur most frequently in large muscle groups during or after exertion in the heat.
• Heat rash occurs in hot, humid environments when sweat ducts become obstructed.

Triage Pearls

Patients presenting with heat-related exposure and any of the following should be referred to a health-care provider for immediate evaluation:

• Hypotension
• Altered mental status
• Tachycardia
• Marked hyperthermia or a history suggesting heat stroke
• Syncope, seizure, severe weakness, or inability to ambulate normally
• Begin active cooling immediately when heat stroke is suspected. Cooling should not be delayed for laboratory testing, intravenous access, imaging, or transport logistics.

History Pearls

• Children, older patients, patients with limited cognitive ability, and those with limited access to air-conditioning or cooling resources are at increased risk for heat illness.
• Athletes and outdoor workers are at risk because of prolonged exposure and physical activity, especially when wearing heavy or impermeable clothing.
• Key elements of a patient’s history include exposure, humidity, duration of exposure, acclimatization status, hydration, exertion, recent illness, alcohol or stimulant use, and medications that can impair thermoregulation or volume status.
• Ask specifically about diuretics, anticholinergic medications, antihistamines, antidepressants, antipsychotics, stimulants, and cardiovascular medications.
• During exertion, advise drinking to thirst rather than forced scheduled overhydration; excessive hypotonic fluid intake can contribute to exercise-associated hyponatremia.

Physical Exam Pearls

• Focus on vital signs, general appearance, skin condition, mental status, and hydration status.
• When severe heat illness is suspected, rectal temperature is the preferred practical measurement of core temperature. Oral, tympanic, temporal, and axillary measurements may substantially underestimate temperature during exertional heat stroke.
• Mental status change is the most important clinical feature separating heat stroke from uncomplicated heat exhaustion.
• Assess for hypotension, tachycardia, tachypnea, signs of dehydration, muscle tenderness, gait abnormality, and evidence of trauma or an alternative cause of altered mental status.

Testing Pearls

Testing should be directed by illness severity. Mild heat illness often requires little or no laboratory testing.

• In suspected heat stroke, do not delay cooling for tests. Arrange emergency transport while treatment is underway.
• When available without delaying transfer, useful tests in moderate or severe illness include electrolytes, glucose, renal function, creatine kinase, hepatic tests, complete blood count, urinalysis, and electrocardiography.
• Coagulation studies are appropriate when heat stroke is suspected because disseminated intravascular coagulation can occur.
• Serum sodium is particularly important in endurance athletes or patients who have consumed large amounts of hypotonic fluid because exercise-associated hyponatremia can resemble heat exhaustion or heat stroke.
• Head computed tomography is not a routine test for heat syncope. Neuroimaging should be based on trauma, persistent neurologic abnormalities, or another specific concern.

Diagnosis Pearls

Table 1 summarizes the common heat urgencies and practical urgent care management.

Classification	Typical findings	Urgent care treatment
Heat stroke	CNS dysfunction; usually marked hyperthermia; may include ataxia, agitation, seizure, obtundation, or coma	Immediate whole-body cooling; EMS/ED transfer; monitor ABCs
Heat exhaustion	Weakness, fatigue, headache, nausea, dizziness, myalgias, tachycardia; no persistent CNS dysfunction	Cool environment; oral isotonic fluids if able; IV isotonic fluids if needed; reassess
Heat syncope	Brief loss of consciousness or presyncope in heat; rapid recovery after supine positioning	Cool environment; supine positioning; oral fluids; evaluate other causes of syncope
Exercise-associated muscle cramps	Painful involuntary contractions during or after exertion	Rest, gentle stretching, oral fluid/electrolyte replacement; no routine potassium supplementation
Heat edema	Dependent extremity swelling after heat exposure	Elevation, compression, acclimatization; avoid routine diuretics
Heat rash	Pruritic papules/vesicles in occluded or sweaty skin	Cool, dry environment; reduce occlusion; symptomatic skin care

Treatment and Disposition Pearls

• Heat stroke is a true emergency. Rapid cooling is treatment, not an adjunct to treatment.
• Cold-water or ice-water immersion is the preferred method of rapid whole-body cooling when it can be performed safely. If immersion is not feasible, use aggressive evaporative and convective cooling over as much body surface area as possible.
• For life-threatening hyperthermia, current resuscitation guidance supports cooling as rapidly as possible, ideally at a rate of at least 0.15°C per minute.
• When using cold-water immersion, discontinue active cooling when core temperature reaches approximately 38.3-38.8°C (101-102°F) to reduce the risk of overshoot hypothermia.
• Do not delay cooling to obtain IV access. If fluids are needed, isotonic oral or IV fluids are appropriate; avoid indiscriminate large-volume free-water intake.
• For patients with suspected heat stroke evaluated in a typical urgent care setting, arrange EMS transfer for hospital evaluation because renal, hepatic, muscular, and coagulation complications can evolve after temperature and mental status improve.
• Heat exhaustion can usually be managed with removal from heat, cooling, oral rehydration when tolerated, and reassessment. Failure to improve promptly, worsening symptoms, persistent tachycardia/hypotension, or mental status abnormality should prompt emergency transfer.
• Do not routinely give potassium for heat cramps. Rest, stretching, and fluid/electrolyte replacement are usually sufficient.
• No medication has a routine role in lowering core temperature in environmental heat stroke.

Medicolegal Pearls

• Document the method and timing of core-temperature measurement, mental status, cooling method, serial temperatures when available, and the response to treatment.
• Document medication, substance-use, environmental, exertional, and hydration risk factors when they may have contributed to heat illness.
• When heat stroke is suspected, document that active cooling began promptly and was not delayed for diagnostic testing or transport arrangements.

Cold Urgencies

Introduction

Exposure to cold temperatures without adequate protection poses an extreme threat to a patient’s life. Although hypothermia presents the greatest immediate systemic risk, frostbite, frostnip, trench foot, and erythema pernio can also produce important morbidity.

Cold-related injury is best approached by first identifying systemic hypothermia and then distinguishing freezing injury from nonfreezing injury. Hypothermia takes priority over treatment of an isolated extremity injury.

Presentation

• Hypothermia is defined as an unintentional core body temperature of 35°C (95°F) or lower. Mild hypothermia often presents with shivering and preserved mental status; progressive confusion, clumsiness, decreased shivering, bradycardia, hypotension, and coma indicate worsening illness.
• Frostbite is associated with numbness, pallor, and firm or frozen tissue. After rewarming, erythema, edema, clear blisters, hemorrhagic blisters, or cyanosis may appear.
• Frostnip is a superficial nonfreezing cold injury with transient numbness and pallor that resolves with warming and does not cause tissue loss.
• Trench foot is a nonfreezing cold injury caused by prolonged exposure to cold, wet conditions; symptoms evolve from numbness and clumsiness to pain, hyperemia, edema, and sometimes neuropathic symptoms after rewarming.
• Pernio (chilblains) causes painful or pruritic erythematous-to-violaceous lesions after cold, damp exposure.

Triage Pearls

• Airways, breathing, and circulation
• Notify a clinician immediately for hypotension, altered mental status, temperature below 32°C (89.6°F), bradyarrhythmia or tachyarrhythmia, respiratory depression, major trauma, or suspected deep frostbite.
• Handle patients with moderate or severe hypothermia gently because a cold myocardium is electrically unstable.
• Remove wet clothing, prevent further heat loss, and begin core rewarming while EMS transfer is arranged for moderate or severe hypothermia.

History Pearls

• Extended immobility elevates the risk of acute renal failure and rhabdomyolysis.
• Risk for frostbite increases with prolonged exposure, wetness, wind, inadequate clothing, dehydration, exhaustion, diabetes, peripheral vascular disease, Raynaud disease, tobacco use, alcohol or drug intoxication, and impaired judgment or mobility.
• Frostbite occurs commonly in patients who are intoxicated, injured, inadequately sheltered, or unable to recognize or respond to progressive numbness.
• Accidental frostbite can occur with prolonged application of ice packs without a proper barrier between the skin and ice pack.
• Ask whether the involved tissue thawed and then refroze; refreezing after thaw causes substantially greater tissue injury.

Physical Exam Pearls

• Classify hypothermia by clinical condition as well as temperature. Core temperature may be difficult to measure accurately, and clinical function becomes increasingly important as the patient becomes colder.
• Mild hypothermia: shivering, cold stress, tachycardia, and preserved ability to cooperate are common.
• Moderate hypothermia: impaired consciousness, reduced shivering, bradycardia, hypoventilation, and decreased motor function may occur.
• Severe hypothermia: profound CNS depression, hypotension, dysrhythmias, pulmonary edema, coma, or cardiac arrest may occur.
• After frostbite has thawed, superficial injury generally produces erythema, edema, and clear blisters; hemorrhagic blisters, cyanosis, absent capillary refill, or injury proximal to the distal interphalangeal joint suggests deep injury.

Testing Pearls

• In moderate or severe hypothermia, obtain continuous cardiac monitoring, glucose, electrolytes, renal function, complete blood count, and other tests guided by the likely cause and complications. Arterial or venous blood gas testing is usually hospital-based.
• Electrocardiographic changes may include interval prolongation, bradyarrhythmia, atrial dysrhythmias, or Osborn (J) waves; their absence does not exclude significant hypothermia.
• Laboratory testing is not routinely necessary for uncomplicated superficial frostbite or frostnip. Deep frostbite requires prompt specialty/ED evaluation; advanced imaging used to predict tissue viability is generally performed after transfer.

Diagnosis Pearls

Table 2 summarizes common cold urgencies and urgent care priorities.

Classification	Typical findings	Urgent care treatment
Mild hypothermia	Usually 32-35°C; shivering; preserved consciousness	Prevent heat loss; remove wet clothing; passive and active external warming; oral calories/fluids if alert
Moderate hypothermia	Usually 28-32°C; impaired consciousness; reduced shivering; bradycardia/hypoventilation	Gentle handling; active core/external warming; cardiac monitoring; EMS/ED transfer
Severe hypothermia	Usually <28°C; coma, hypotension, dysrhythmia, cardiac arrest	Full resuscitation while rewarming; EMS transport to appropriate center; consider ECLS-capable destination
Frostbite	Frozen/numb tissue; after thaw, edema/blisters; deep injury may be cyanotic or hemorrhagic	Treat hypothermia first; rapid water rewarming 37-39°C only if refreezing can be prevented; protect and transfer deep injury
Frostnip	Transient pallor/numbness without tissue freezing	Shelter and gentle warming; no tissue-loss treatment required
Trench foot	Wet-cold exposure; numbness then pain, edema, hyperemia	Drying, elevation, passive rewarming, analgesia; avoid aggressive rapid heating
Pernio	Pruritic/painful erythematous or violaceous lesions	Keep warm and dry; symptomatic care; evaluate persistent/severe cases

Treatment and Disposition Pearls

• Mild hypothermia can usually be treated by preventing further heat loss, removing wet clothing, providing insulation, and using passive or active external warming. Alert patients may receive warm oral fluids and calories.
• Moderate or severe hypothermia requires emergency transfer. Warm the trunk/core, use warm blankets or forced-air warming when available, and avoid unnecessary movement of the patient.
• In hypothermic cardiac arrest, perform full resuscitation while rewarming. Current resuscitation guidance recognizes that patients may survive prolonged arrest and supports transport to an extracorporeal life support-capable center when feasible.
• For frostbite, treat coexisting hypothermia first. If there is no risk of refreezing, rapidly rewarm the affected area in circulating water maintained at 37-39°C (98.6-102.2°F) until tissue is soft and pliable, generally about 30 minutes.
• Do not rub frostbitten tissue, apply snow, use heating pads or direct dry heat, or allow thawed tissue to refreeze.
• After thawing, elevate the injured part, apply loose bulky dry dressings, protect from trauma, and avoid walking on a thawed frostbitten foot when possible.
• Ibuprofen may be used for pain and its anti-inflammatory effect when not contraindicated. Topical aloe vera may be applied to thawed tissue. Routine prophylactic antibiotics are not indicated without evidence of infection.
• Deep frostbite is time-sensitive. Transfer promptly to an ED, burn center, or frostbite-experienced center because advanced therapies may be considered. Iloprost was approved by the FDA in 2024 for severe frostbite to reduce the risk of digit amputation and is most useful when started early after rewarming.
• Do not routinely debride or unroof hemorrhagic blisters in urgent care. Blister management and advanced tissue-salvage decisions are best coordinated with experienced specialty care.
• Trench foot is a nonfreezing injury; dry the feet, elevate, provide analgesia, and use gradual/passive rewarming rather than aggressive hot-water rewarming.

Medicolegal Pearls

• Document the core-temperature method, mental status, cardiac rhythm when monitored, rewarming methods, and response to treatment.
• For frostbite, document whether tissue was frozen or already thawed, whether refreezing remained possible, the water temperature used for rewarming, distal perfusion, blister type, and the timing of transfer.
• Document environmental exposure, wet clothing, intoxication, medications, comorbidities, mobility limitations, and social circumstances when they affect risk or disposition.
• Do not delay emergency transfer for severe hypothermia or deep frostbite to complete nonessential urgent care testing.

References

1. 1. Eifling KP, Gaudio FG, Dumke C, et al. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness: 2024 Update. Wilderness Environ Med. 2024;35(1 suppl):112S-127S. doi:10.1177/10806032241227924.
2. 2. McIntosh SE, Freer L, Grissom CK, et al. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Frostbite: 2024 Update. Wilderness Environ Med. 2024;35(2):183-197. doi:10.1177/10806032231222359.
3. 3. Dow J, Giesbrecht GG, Danzl DF, et al. Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. Wilderness Environ Med. 2019;30(4 suppl):S47-S69. doi:10.1016/j.wem.2019.10.002.
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5. 5. American Heart Association. Part 10: Adult and Pediatric Special Circumstances of Resuscitation. In: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2025.
6. 6. Centers for Disease Control and Prevention. Heat and Cold Illness in Travelers. CDC Yellow Book 2026. Updated April 23, 2025.
7. 7. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. Cold-Related Illnesses in Workers. Reviewed 2026.