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Cooling Techniques for Hyperthermia

  • Author: Erik D Schraga, MD; Chief Editor: Asim Tarabar, MD  more...
Updated: Dec 14, 2015


Heat illness is a pervasive problem that is often encountered in patients who present to the emergency department. During summer heat waves, large urban centers see a significant rise in hyperthermia-related fatalities. Heat illness should be thought of as a spectrum of disease from heat cramps to heatstroke. Medication-related hyperthermic conditions such as malignant hyperthermia, serotonin syndrome, and neuroleptic malignant syndrome (NMS) need to be specifically recognized, as the treatment of these diseases requires adjunctive pharmacotherapy (eg, dantrolene, cyproheptadine, bromocriptine, levodopa, amantadine) in addition to rapid cooling measures. Understanding basic principles of thermoregulation and the pathophysiology of hyperthermia are essential to treatment.[1, 2]

The image below depicts items used for noninvasive cooling techniques.

Sample display of equipment useful for noninvasive Sample display of equipment useful for noninvasive cooling techniques. Clockwise from top: ice pack and water, air-cooling blanket, Foley catheter, and intravenous fluids.

See Heat Illness: How To Cool Off Hyperthermic Patients, a Critical Images slideshow, for tips on treatment options for patients with heat-related illness.

Also, see Football Injuries: Slideshow to help diagnose and treat injuries from a football game, including heatstroke, a major concern in college and high school football.

Effective thermoregulation, controlled by the hypothalamus, is critical for proper function of the human body, with normal temperature exhibiting diurnal variation between 36-37.5°C. Heat is both produced endogenously and acquired from the environment. Metabolic reactions in human bodies are exothermic, contributing 50-60 kcal/h/m2 of body surface area, or 100 kcal/h for a 70-kg person. During strenuous exercise, heat production increases 10- to 20-fold.[3] Environmental heat transfer involves the following 4 mechanisms[3] :

  • Conduction: Direct physical contact transfers heat from a warmer object to a cooler object. Water is about 25 times more effective than air at conducting heat.
  • Convection: Heat is transferred through air and water vapor molecules surrounding the body. Convective heat transfer depends on wind velocity and explains the effect of wearing loose-fitting clothing in warm climates to keep cool.
  • Radiation: Heat is transferred by electromagnetic waves. Radiation is the major source of heat gain in hot ambient climates; up to 300 kcal/h can be gained on a hot summer day.
  • Evaporation: The conversion of a liquid to a gas results in heat transfer. One liter of sweat from the body results in a loss of 580 kcal of heat.

Hyperthermia is defined as elevated core temperature of greater than 38.5°C (101.3°F). History and clinical examination can help elucidate the etiology of hyperthermia and tailor treatment. The causes of hyperthermia include the following[4] :

  • Increased ambient heat - Heat waves, humidity
  • Increased heat production - Overexertion, thyroid storm, malignant hyperthermia, neuroleptic malignant syndrome, pheochromocytoma, delirium tremens, hypothalamic hemorrhage, toxic ingestions (eg, sympathomimetics, anticholinergics, ecstasy)
  • Decreased heat dissipation - Humid environment, poor sweat production

Sweating and peripheral vasodilation are major mechanisms of heat loss to maintain proper temperature. In the absence of these mechanisms, baseline temperature would increase 1.1°C per hour from basal metabolism alone.[4] Sweat cools the body through evaporation, and peripheral vasodilation provides the blood flow and heat necessary to evaporate the sweat. During periods of high environmental heat and humidity, evaporative cooling can become insufficient, leading to heat illness.

Patients at risk for heat illness include the following[5, 6] :

  • Athletes exercising strenuously in hot climates
  • Elderly patients (because of decreased efficacy of thermoregulation, comorbid illness or medications, lack of fans or air conditioning, inappropriate dress)
  • Infants and small children (because of high ratio of surface area to weight, inability to control fluid intake)
  • Patients with cardiac disease or those taking beta-blockers (because of inability to increase cardiac output sufficiently for vasodilation)
  • Patients who are dehydrated because of poor fluid intake, gastroenteritis, and diuretic or alcohol use (Dehydration increases demand on ATPase pumps, which contribute 25-45% of basal metabolic rate.)
  • Patients prone to higher endogenous heat production (eg,  infection, thyrotoxicosis)
  • Patients taking medications that inhibit sweat production or increase heat production (eg, anticholinergics, antidepressants, antihistamines, neuroleptics, zonisamide, sympathomimetics, lithium, alpha- and beta-blockers)

Recognizing the clinical signs associated with heat illness determines the appropriate therapy, from fluid replacement for heat exhaustion to rapid aggressive cooling for heatstroke.[5, 4, 6]

Symptoms of heat exhaustion include the following:

  • Normal to slightly elevated core temperature
  • Fatigue or malaise
  • Orthostatic hypotension, tachycardia
  • Clinical signs of dehydration
  • Nausea, vomiting, diarrhea (due to splanchnic and renal vasoconstriction)
  • Intact mental status
  • Responsive to cool environment, fluid and electrolyte replacement

Symptoms of heatstroke include the following:

  • Elevated core temperature, usually greater than 40.5°C
  • Vague prodrome of weakness, nausea, vomiting, headache
  • CNS symptoms including confusion, ataxia, coma, seizures, delirium
  • Hot, dry skin
  • Hyperdynamic cardiovascular response [7] (high central venous pressure [CVP], low systemic vascular resistance [SVR], tachycardia)
  • Elevation of hepatic transaminases, usually in the tens of thousands range
  • Coagulopathy
  • Rhabdomyolysis and renal failure

This article focuses specifically on rapid cooling techniques for hyperthermic patients, a critical action in the initial resuscitation of patients with heatstroke. In fact, rapid cooling may be the single most important action to prevent death or permanent disability. To mitigate organ damage, the goal should be to reduce rectal temperature to below 40°C within 30 minutes of beginning cooling therapy.[6, 8]



Indications are as follows:

  • Elevated rectal temperature greater than 40°C and altered mental status
  • Particularly aggressive temperature reduction is necessary in the setting of hemodynamic instability.
  • Suspected or confirmed neuroleptic malignant syndrome and malignant hyperthermia: Cooling techniques should be administered concomitantly with administration of dantrolene. [9]  The offending drug should be discontinued.


Treatment of hyperthermia with cooling techniques has no absolute contraindications.

Relative contraindications to specific cooling modalities include the following:

  • Ice water immersion - Inability to perform cardiac monitoring, limited patient supervision
  • Gastric lavage - Inability to protect airway unless patient is endotracheally intubated
  • Peritoneal lavage - Multiple previous abdominal surgeries (relatively contraindicated because of increased risk of bowel perforation)


Anesthesia is not typically necessary unless invasive procedures are indicated, including cardiopulmonary bypass or peritoneal lavage.

For highly invasive procedures or refractory hyperthermia, paralysis may be necessary to extinguish shivering and reduce endogenous heat production; therefore, patients may require sedation for supportive mechanical ventilation.[10] See the Medscape Drugs & Diseases topic on Tracheal Intubation, Rapid Sequence Intubation for more detail.



Noninvasive external cooling

See the list below:

  • Ice packs
  • Spray bottle
  • Tepid (15°C) water
  • Fan
  • Cooling blanket
  • Ice bath (eg, bathtub, decontamination tub, child’s wading pool)
  • Crystalloid intravenous fluids
  • Rectal thermometer probe

Noninvasive external cooling equipment is shown below.

Sample display of equipment useful for noninvasive Sample display of equipment useful for noninvasive cooling techniques. Clockwise from top: ice pack and water, air-cooling blanket, Foley catheter, and intravenous fluids.

Gastric lavage

See the list below:

Gastric lavage equipment is shown below.

Sample display of equipment useful for cooling via Sample display of equipment useful for cooling via gastric lavage. Clockwise from top: ice water, nasogastric tube, endotracheal tube, and lavage bag.

Peritoneal lavage

See the list below:

  • Peritoneal catheter set
  • Normal saline
  • Ice bath

Peritoneal lavage equipment is shown below.

Sample display of equipment useful for cooling via Sample display of equipment useful for cooling via peritoneal lavage. Clockwise from top: iced water, peritoneal catheter, and saline fluid.


Patients may be placed supine, as this is the most practical position for performing other interventions (eg, intravenous access, endotracheal intubation) that are likely to be performed concomitantly with cooling.



Noninvasive external cooling

Evaporative cooling

This is a fast and efficient noninvasive technique for cooling moderate hyperthermia. It was reported in volunteers that it reduces core body temperature by approximately 0.3°C per minute; however, in heatstroke patients, it reduced core body temperature significantly slower: from 0.05°C to 0.09°C per minute.[11]

Remove all of the patient’s clothing.

Insert a rectal thermometer for continuous monitoring.

Mist over patient constantly, using spray bottles filled with tepid (15°C) water.

Place large fans to circulate warm room air (ideally 40°C) directed at the patient.

Ice water immersion

This is the fastest and most efficient noninvasive technique for cooling. This technique involves immersing the patient in an ice water bath, which results in reduction of core temperature approximately 0.15-0.35°C per minute.[11, 12, 13, 14]

The vasoconstriction induced by ice water can be beneficial to patients experiencing hypotension. This technique is safe when used for patients suffering from exertional heatstroke (eg, athletes, military recruits) but caution should be used with patients suffering from classic heatstroke (eg, elderly patients, patients with alcoholism) who have been reported to have a mortality rate up to 14% associated with this cooling method.

Remove all of the patient’s clothing.

Position the patient in tub of water (0-15°C) so that the patient’s chest and extremities are completely immersed with the head supported outside of the tub.

If necessary, administer benzodiazepines to control shivering.

Remove the patient once core temperature reaches 39°C to avoid overshoot hypothermia.

Whole-body ice packing

This technique has the advantage of not requiring constant supervision. It can reduce core temperature approximately 0.03°C per minute.[5]

Remove all of the patient’s clothing.

Position the patient on plastic sheets or in a child’s plastic pool.

Cover the patient’s chest and extremities with crushed ice.

Remove the patient once core temperature reaches 39°C.

Strategic ice packing

This is a commonly used technique, often used in conjunction with evaporative cooling, that reduces core temperature approximately 0.02-0.03°C per minute.[5]

Remove all of the patient’s clothing.

Place ice packs in the patient’s groin, in the axillae, and around the anterior neck.

Remove ice packs once core temperature reaches 39°C.

Invasive core cooling in conjunction with external cooling techniques

Gastric lavage

Because gastric mucosa does not significantly vasoconstrict and the stomach lies in close proximity to the liver and inferior vena cava, gastric lavage is a reasonable method to rapidly cool hyperthermic patients. A core temperature reduction of approximately 0.15°C per minute can be achieved using this method.

Secure the patient’s airway.

Place a large-bore nasogastric or orogastric tube. (For details, see Clinical Procedures article Nasogastric Tube.)

Cut open a lavage bag and add water or normal saline and ice.

Hang the bag above the patient and connect to gastric tube using Y connector. Connect the other end of the Y connector to suction.

Rapidly instill 10 mL/kg of ice water (not ice) over 30-60 seconds.

Remove water with suction after 30-60 seconds.

Peritoneal lavage

Because of the large surface area of the peritoneum, peritoneal lavage is highly effective as a cooling technique. This technique can produce core body temperature reductions of 0.5°C per minute or up to 5-10°C per hour.[5] An advantage of peritoneal lavage over gastric lavage is that patients do not need to be endotracheally intubated. However, peritoneal lavage does require equipment and skilled personnel to surgically place the peritoneal catheter.

While preparing for the placement of the peritoneal catheter, prepare the lavage by placing 2-8 L of normal saline into an ice bath.

Place a standard peritoneal catheter.

Instill and withdraw ice cold saline in 500-1000 mL increments until the patient’s core body temperature reaches 39°C.



Antipyretics are not effective in treating environmental hyperthermia.

Use intravenous fluids modestly in the setting of hypotension and hyperthermia to avoid worsening pulmonary edema. Cooling is the treatment of choice to cause peripheral vasoconstriction and reduce venous pooling.

Consider using short-acting benzodiazepines to reduce agitation and shivering during initial cooling as well as to treat hyperthermia due to sympathomimetic ingestion.

Coagulopathy is a common physiologic response to hyperthermia; be sure to monitor for disseminated intravascular coagulopathy (DIC).

Consider a trial of glucose in any patient with altered mental status.

Avoid rapid replacement of free water, as hyponatremia and cerebral edema may develop.



Complications vary by cooling technique.

Evaporative cooling

Complications from this technique are rare.

Wet skin can interfere with cardiac monitoring.

Ice water immersion

Complications include patient discomfort or shivering.

Cardiac monitoring is difficult underwater.

Resuscitation is difficult underwater. If patient develops ventricular fibrillation, he or she must be removed and completely dried prior to defibrillation.

This technique is labor-intensive.

Whole-body ice packing

Complications include patient discomfort or shivering.

Overshoot hypothermia (cooling core body temperature to less than 39°C) must be avoided.

Cardiac monitoring is difficult with this technique.

Strategic ice packing

Complications include patient discomfort or shivering.

Overshoot hypothermia (cooling core body temperature to less than 39°C) must be avoided.

Prolonged skin contact to ice can cause cold injuries.

Gastric lavage

Aspiration is a risk if the patient’s airway is not protected.

The potential for hyponatremia or water intoxication can be avoided by using normal saline.

Peritoneal lavage

This technique can result in falsely low rectal temperature readings. To avoid this, use tympanic or esophageal measurements instead.

The bladder or bowel can be perforated.

The catheter can be inadvertently placed into the rectus sheath instead of the peritoneum.


Refractory Cases

For refractory cases of hyperthermia, the following techniques can be considered in consultation with the intensive care unit team:

  • Cardiopulmonary bypass
  • Cool air pulmonary jet ventilation
  • Iced water rectal lavage
  • Hemodialysis
  • Intravascular cooling (This technique has been successful in a few cases but is not a currently validated therapy for hyperthermia. [15] )
Contributor Information and Disclosures

Erik D Schraga, MD Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates

Disclosure: Nothing to disclose.


Laura W Kates, MD Emergency Physician, Swedish Cherry Hill Medical Center, Seattle, WA

Laura W Kates, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, Physicians for Social Responsibility, Wilderness Medical Society, Emergency Medicine Residents' Association, Physicians for Human Rights

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Chief Editor

Asim Tarabar, MD Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital

Disclosure: Nothing to disclose.

Additional Contributors

Luis M Lovato, MD Associate Clinical Professor, University of California, Los Angeles, David Geffen School of Medicine; Director of Critical Care, Department of Emergency Medicine, Olive View-UCLA Medical Center

Luis M Lovato, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

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Sample display of equipment useful for noninvasive cooling techniques. Clockwise from top: ice pack and water, air-cooling blanket, Foley catheter, and intravenous fluids.
Sample display of equipment useful for cooling via gastric lavage. Clockwise from top: ice water, nasogastric tube, endotracheal tube, and lavage bag.
Sample display of equipment useful for cooling via peritoneal lavage. Clockwise from top: iced water, peritoneal catheter, and saline fluid.
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