Cooling Techniques for Hyperthermia

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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. Patients may also present with hyperthermia as a consequence of agitated delirium states, which require sedation in addition to aggressive cooling. Understanding basic principles of thermoregulation and the pathophysiology of hyperthermia is essential to treatment. ^{[1, 2]}

The image below depicts items used for noninvasive cooling techniques.

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 conductive (more effective at conducting heat) than air.

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.

Phase change: The conversion of a solid to a liquid (melting) or a liquid to a gas (evaporation) results in heat transfer. Evaporation of 1 L 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, MDMA)

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, alpha- and beta-blockers), especially in hot weather; deaths from cocaine are markedly increased when the ambient temperature increases ^[7]

Recognizing the clinical signs associated with heat illness determines the appropriate therapy, from fluid replacement for heat exhaustion to rapid aggressive cooling for heatstroke. ^{[4, 5, 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 ^[8] (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, 9]}

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 implemented concomitantly with administration of specific pharmacologic treatment (eg, dantrolene for malignant hyperthermia). ^[10] 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. ^[11] See the Medscape Drugs & Diseases topic on Rapid Sequence Intubation for more detail.

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.

See the list below:

Nasogastric tube

Ice water

Endotracheal intubation equipment, if airway needs to be protected (see Rapid Sequence Intubation)

Y connector

Lavage bag

Gastric lavage equipment is shown below.

See the list below:

Peritoneal catheter set

Normal saline

Ice bath

Peritoneal lavage equipment is shown below.

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.

Evaporative cooling

This is a 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 more slowly: from 0.05°C to 0.09°C per minute. ^[12]

Remove all of the patient’s clothing.

Insert a rectal probe 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, and it should be the first-line treatment for patients with severe hyperthermia of any etiology. 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. ^{[12, 13, 14, 15]}

The vasoconstriction induced by ice water can be beneficial to patients experiencing hypotension. This technique is safe when used for patients with exertional heatstroke (eg, athletes, military recruits), but caution should be used in patients with classic heatstroke (eg, elderly patients, patients with alcoholism), who have been reported to have a mortality rate of up to 14% associated with this cooling method. However, even in these patients, the benefits of rapid cooling usually outweigh the risks of the procedure.

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 a tub is unavailable, an unsealed body bag may be used.

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 and in the axillae. Ice packs around the neck should be avoided to prevent interference with thermoregulation in the brain.

Remove ice packs once core temperature reaches 39°C.

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 benzodiazepines to reduce agitation and shivering during initial cooling and 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.

Complications from this technique are rare.

Wet skin can interfere with cardiac monitoring.

Cooling by this technique can be slow, and it is insufficient for patients with severe hyperthermia.

Complications include patient discomfort or shivering.

Cardiac monitoring is difficult underwater.

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

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

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.

Complications include patient discomfort or shivering.

Prolonged skin contact with ice can cause cold injuries.

This technique is not very effective and is insufficient for patients with significant hyperthermia.

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.

This technique is labor-intensive.

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.

This technique is labor-intensive.

The time to place the catheter may delay cooling.

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. ^[16] )

However, because ice water immersion is so effective, these methods are rarely necessary.

Overview

What is hyperthermia?

What is the pathophysiology of hyperthermia?

What causes hyperthermia?

Who is at risk for hyperthermia?

What are the signs and symptoms of heat exhaustion in hyperthermia?

What are the signs and symptoms of heatstroke in hyperthermia?

When is cooling indicated for the treatment of hyperthermia?

What are the contraindications to cooling for the treatment of hyperthermia?

What is the role of anesthesia in cooling treatments for hyperthermia?

What equipment is needed to perform noninvasive external cooling for hyperthermia?

What equipment is needed to perform gastric lavage for hyperthermia?

What equipment is needed to perform peritoneal lavage for hyperthermia?

How are patients positioned for the administration of cooling for hyperthermia?

How is evaporative cooling performed in the treatment of hyperthermia?

How is ice water immersion cooling performed in the treatment of hyperthermia?

How is whole-body ice packing cooling performed in the treatment of hyperthermia?

How is strategic ice packing cooling technique for hyperthermia?

How is gastric lavage cooling performed in the treatment of hyperthermia?

How is peritoneal lavage cooling performed in the treatment of hyperthermia?

What are pearls for the use of cooling in the treatment of hyperthermia?

What are the possible complications of evaporative cooling for hyperthermia?

What are the possible complications of ice water immersion cooling for hyperthermia?

What are the possible complications of whole-body ice packing cooling for hyperthermia?

What are the possible complications of strategic ice packing cooling for hyperthermia?

What are the possible complications of gastric lavage cooling for hyperthermia?

What are the possible complications of peritoneal lavage cooling for hyperthermia?

How is refractory hyperthermia treated?

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Plattner O, Kurz A, Sessler DI, Ikeda T, Christensen R, Marder D, et al. Efficacy of intraoperative cooling methods. Anesthesiology. 1997 Nov. 87(5):1089-95. [Medline].

McDermott BP, Casa DJ, Ganio MS, Lopez RM, Yeargin SW, Armstrong LE, et al. Acute whole-body cooling for exercise-induced hyperthermia: a systematic review. J Athl Train. 2009 Jan-Feb. 44(1):84-93. [Medline].

Smith JE. Cooling methods used in the treatment of exertional heat illness. Br J Sports Med. 2005 Aug. 39 (8):503-7; discussion 507. [Medline].

Broessner G, Beer R, Franz G, Lackner P, Engelhardt K, Brenneis C, et al. Case report: severe heat stroke with multiple organ dysfunction – a novel intravascular treatment approach. Crit Care. 2005 Oct 5. 9(5):R498-501. [Medline].

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.

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.

Sage W Wiener, MD Assistant Professor, Department of Emergency Medicine, State University of New York Downstate Medical Center; Director of Medical Toxicology, Department of Emergency Medicine, Kings County Hospital Center

Sage W Wiener, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Medical Toxicology, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

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.

Cooling Techniques for Hyperthermia

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