Chapter 190. Hyperthermic Patient Management

The heatstroke victim can be difficult and challenging, even after a successful resuscitation and stabilization in the Emergency Department. Heatstroke is a multisystem insult. More than 300 people die of heat-related illness in the United States each year.1 This number was surpassed in a single week in 1995 during a heat wave in Chicago.2–6 This heat wave resulted in more than 400 deaths and 3300 Emergency Department visits. Although heatstroke is an uncommon medical emergency, it is considered one of the most important of all the environmental heat illnesses because of its potential for high morbidity and mortality in large numbers.7 Major complications of heatstroke include seizures, adult respiratory distress syndrome (ARDS), acute renal failure, liver disease, rhabdomyolysis, disseminated intravascular coagulation, and death.8 Survival is possible for the great majority of patients with rapid recognition and aggressive management.

The most effective means of cooling remains controversial. The techniques rely upon prompt recognition of symptoms, immediate intervention in the field, and immediate intervention in the Emergency Department. Begin cooling the patient in the prehospital setting by removing the patient from the heat stress, keeping their skin wet, and fanning the patient in transport. The patient must be exposed adequately and cooling must be initiated in the quickest and most efficient manner possible as stabilization is occurring.

Cooling measures must be modified to avoid hypothermia once the core temperature reaches 39°C or 102°F. Decreasing the core body temperature to less than 39°C or 102°F within 30 minutes of presentation improves survival.4 Cooling must precede the investigation for the cause. Evaporation and convection are the simplest and most efficient means of cooling victims of heatstroke or heat exhaustion. Evaporation of 1 g of water dissipates approximately seven times more heat than melting the same quantity of ice.4 Skin blood flow is preserved as compared with the use of ice, because evaporation and convection are much more efficient modes of heat exchange.9

The information in this chapter primarily pertains to hyperthermia from heat-related illness. Despite this, some of these techniques may be used for other causes of hyperthermia. These include endocrine disorders, head injury, infection, intracranial hemorrhage, malignant hyperthermia, neuroleptic malignant syndrome, sepsis, serotonin syndrome, stroke, toxins, or other causes. Consider discussing the use of these techniques to treat hyperthermia with the appropriate consultant if the etiology is not heat-related.

Heat-related illness comprises a spectrum of symptoms ranging from mild heat edema to heatstroke. Heat edema is self-limited. The patient presents with edema of the hands, feet, and ankles. This usually occurs in the first few days of heat acclimatization. Heat cramps occur most often in individuals who sweat profusely and are exercising or walking. The patient consumes water without salt, resulting in hyponatremia and muscle cramps. Heat syncope is dizziness or syncope after exposure to high temperatures. It is caused by vasodilatation and consequent postural hypotension. Heat exhaustion results from the excessive loss of body water, electrolytes, or both. The patient may complain of headache, nausea, vomiting, malaise, and myalgias. Heat exhaustion is distinguished from heatstroke by a normal mental status and, generally, a temperature below 39°C or 102°F.2,8

Heatstroke must be suspected in any patient who has acute mental status changes or other signs of central nervous system dysfunction in the setting of a high temperature and a history of heat exposure. The initial temperature is usually at least 40 to 42°C or 104 to 108°F. Central nervous system dysfunction may manifest as varying degrees of confusion, obtundation, seizures, delirium, or focal deficits.

Core body temperature is maintained within close limits by a balance between heat production and heat dissipation. Muscular and metabolic activity generates heat. Most fevers encountered are a response to microbial invasion. Some fevers are due to exposure to high temperatures or abnormalities in the thermoregulatory apparatus.10 Heatstroke may occur in previously healthy individuals who are subjected to severe environmental thermal stress, usually during extreme physical exertion. It may occur in patients with compromised homeostatic mechanisms who are subjected to lesser degrees of exposure (classic heatstroke). Factors that may compromise protective thermoregulatory mechanisms include chronic illness, psychiatric disorders, cardiovascular disease, endocrine disorders, nutritional deficiencies, metabolic disorders, infection disorders, medications, substance abuse, poor judgment, or extremes of age (Table 190-1).8

It has been speculated that oxidative phosphorylation becomes uncoupled and enzyme systems cease to function when temperature regulation is lost and the core body temperature exceeds 42°C or 108°F. Energy stores become depleted as maximum metabolic demands escalate. This causes the cell membranes to become increasingly permeable, thus increasing sodium influxes. These phenomena have been postulated to be part of a positive feedback loop involving progressive depletion of ATP, increased ion flux, increased rates of membrane depolarization and neurotransmitter activity, and a subsequent increase in heat production. Cell membranes eventually lose their integrity. Heat production accelerates, proteins denature, and widespread necrosis occurs as temperature-control mechanisms fail, leading to organ failure. Cellular damage occurs as a result of the elevated temperatures and the length of exposure to heat.8,11,12 Tissues at greatest risk for heat-related damage include the vascular endothelium, neural tissue, hepatocytes, and the kidneys.

Heat is dissipated by a combination of radiation, convection, conduction, and evaporation.10 Radiation is the transfer of heat to objects not in direct contact with the subject. Radiation accounts for approximately 65% of heat loss in cool environments. It is a major source of heat gain in hot climates. Convection is the transfer of heat to circulating fluid or gas. The amount of heat dissipated by convection becomes minimal as ambient temperature rises. Convective heat loss varies directly with wind velocity. Conduction is the direct transfer of heat to another object by direct contact. Evaporation is the conversion of a liquid to the gaseous phase. Evaporation becomes the dominant mechanism of heat loss as ambient temperatures rise.4,11

Cooling will not harm patients who are hyperthermic, regardless of the etiology. Cooling can be lifesaving in those with true heatstroke. Heatstroke may be difficult to identify if cooling was initiated in the field and the patient's mental functioning is intact. Initiate cooling immediately if there is any doubt.8

Patient stabilization always remains the top priority. Assess the patient's airway, breathing, and circulation first, despite the need for immediate cooling. Any life-threatening or limb-threatening conditions must be addressed simultaneously or before proceeding to cooling measures.

Do not initially waste time with typical fever treatments. The use of antipyretics such as acetaminophen and nonsteroidal anti-inflammatory drugs are not effective in treating hyperthermia due to heat-related illness. Do not administer medications used to treat malignant hyperthermia, neuroleptic malignant syndrome, or serotonin syndrome.13 These treatments do not work for heat-related hyperthermia.

There are specific contraindications to the individual cooling techniques. Iced gastric lavage is contraindicated in patients with altered mental status or depressed airway reflexes unless the patient is endotracheally intubated. It is also contraindicated if nasogastric intubation (Chapter 58) is contraindicated. Iced peritoneal lavage is contraindicated if the placement of a peritoneal lavage catheter (Chapter 66) is contraindicated. Refer to Chapters 58 and 66 for the complete details of placing these devices.

• Core thermometer (e.g., esophageal, rectal, or urinary)
• Large fans
• Spray bottles with a misting nozzle
• Water
• Ice
• Immersion tub
• Ice packs
• Wet sheets and towels
• Cooling blanket
• Peritoneal lavage kits
• Nasogastric tubes
• Iced saline

Immediately remove the patient from the heat-stress environment. Explain the cooling techniques to be employed to the patient and/or their representative. Remove the patient's clothes. Stabilize the patient's airway, breathing, and circulation as necessary. Patient outcome is directly related to the length of time the tissues are exposed to the thermal challenge. Cooling rates should not exceed 0.1 to 0.2°C per minute. Apply cardiac rhythm monitoring, a noninvasive blood pressure cuff, and pulse oximetry. Place an esophageal (if the patient is intubated), rectal, or urinary temperature probe to monitor the patient's core body temperature.

Evaporation

This technique is simple and causes very little to no discomfort to the conscious patient. An additional benefit is access to the patient should other interventions be necessary.4 Wet the exposed patient with tepid water. Place large and powerful fans to strategically direct high-flow air currents toward the patient's head, feet, and torso (Figure 190-1). Spray the patient with a mist of water from the spray bottles. Keeping the patient “wet and windy” provides a state-of-the-art cooling method for even the smallest Emergency Department without the need to purchase new or specialized equipment. Place ice packs wrapped in wet towels on the patient's groin, axilla, and neck.

Discontinue evaporative cooling when the core body temperature reaches 39°C or 102°F. Continued cooling can result in hypothermia as the core temperature continues to decrease after evaporative cooling is discontinued. Monitor the patient to ensure that their core body temperature does not increase.

The concept of evaporative cooling gained popularity with the Makkah Body Cooling Unit (BCU). The BCU is used today to provide field treatment for people participating in the annual pilgrimage to Mecca who may develop heatstroke. The BCU has been found to provide the fastest core temperature cooling rates of 0.31°C/min.11

Ice Water Immersion

Immersion in an ice water bath is a common method of cooling heatstroke patients. Place the patient in a tub of ice water for 10 to 40 minutes (Figure 190-2). Briskly massage the patient's extremities to maintain peripheral circulation and promote heat loss. Monitor the patient's core temperature carefully. Rectal temperatures will decrease approximately 0.16 to 0.21°C/min.8,11

Ice water immersion is recommended by some authors as the initial technique for hyperthermia management.6,13,14 Unfortunately, it has limited use in the Emergency Department.4,11 Preparing an ice bath can result in a delay in cooling the patient. Contact with the ice water results in intense vasoconstriction, which blocks heat exchange, paradoxically increases core body temperature, induces shivering, and is uncomfortable for the patient. Heat transfer from the core to the surface is reduced. The practical issues of impairing access to the patient, monitoring the airway, and initiating resuscitative measures are challenging when the patient is in an ice water bath.4,11,15 The tub and patient lift device are large, bulky, and not often available in the Emergency Department. Multiple caregivers are required to prevent the patient from drowning and to maintain their head above water.

A simpler and easier method is immersion of just the patient's hands and forearms.16 This method requires less patient cooperation than full body immersion. It also allows for full patient monitoring during the cooling process.

Ice Packing

Packing the heatstroke patient in ice is an alternative to ice water immersion. It can result in conductive heat loss that is as effective as evaporative cooling. Patients who are awake and alert do not often tolerate ice packing. Its use may require parenteral sedation. The complications and practical limitations are similar to those of ice water immersion.

Place the undressed patient in the center of the gurney. Completely cover the patient with ice. This technique requires a large quantity of ice, which may be unavailable in the Emergency Department. Consider placing plastic sheets or trash bags, with the edges curved upward, under the patient to prevent the ice and water from spilling onto the floor, as healthcare personnel may otherwise slip on the wet floor, fall, and sustain injuries. An easier alternative is to place the patient in a body bag and fill this with ice. Discontinue cooling when the core temperature reaches 39°C or 102°F.

Ice Packs

The placement of ice packs over select body areas is a more reasonable option than ice water immersion or ice packing. It may be used as the sole cooling method or in conjunction with evaporative cooling. Place plastic bags filled with ice or ice water in the patient's axilla and groin. Remove the ice packs when the core temperature reaches 39°C or 102°F.

Iced Peritoneal Lavage

Peritoneal lavage in hyperthermia has been investigated in canine models but used infrequently in humans. The advantages of this technique include the large surface area exposed to iced saline and direct cooling of the core. This technique is invasive, time-consuming, requires significant equipment and expertise, and is associated with significant complications. A case report indicated that iced peritoneal lavage with 2 L of normal saline was successful in decreasing the rectal temperature to 39.5°C or 103°F.9 The patient had responded only partially to external evaporative cooling and iced gastric lavage. Place 1 L bags of saline or Ringer's lactate solution into an ice water bath to cool down. The technique is similar to that used for warming the hypothermic patient. Refer to Chapter 189 for the complete details of this technique. Iced peritoneal lavage should be reserved for the patient who is not responding to other methods of cooling.

Iced Gastric Lavage

Central cooling techniques have not been studied extensively. An alternative core cooling technique is iced gastric lavage. This method has been compared to room-air cooling in an anesthetized canine heatstroke model.10 Gastric lavage with iced tap water cooled the canine models rapidly and safely. The technique yielded cooling rates five to six times faster than in controls. Significant differences in hemodynamic parameters were noted to return to baseline more quickly in the iced gastric lavage group than in the control group. The technique is similar to that used for warming the hypothermic patient. Refer to Chapter 189 for the complete details of this technique. Instill 10 mL/kg of iced sterile saline, allow it to dwell for 30 to 60 seconds, and suction out the fluid. Repeat the procedure as necessary. Potential hazards using this technique include aspiration, gastric mucosal injury, electrolyte imbalances with water lavage, and dysrhythmias.10

There has been much research in the last decade regarding the induction of therapeutic hypothermia. This research has primarily focused on those with brain injury, postcardiac arrest, and stroke. This has resulted in the development of a variety of externally applied and internally applied cooling devices. While not specifically designed to treat hyperthermia, they can easily be used to manage the hyperthermic patient. Refer to Chapter 188 for a discussion of these cooling methods and devices.

Monitor core body temperature closely with an esophageal, rectal, or urinary temperature probe. Monitor the patient's vital signs, neurologic function, urine output, and laboratory measurements (arterial blood gases and serum electrolytes). Consider monitoring central venous pressure and pulmonary artery pressure, especially in patients with heatstroke and limited cardiac reserve. Volume deficits may not be more than 2 to 3 L, especially in patients with classic heatstroke. Hypotension usually responds to intravenous fluids. If required, use an inotrope that produces little vasoconstriction, such as dobutamine. The use of H2 blockers may decrease the incidence of gastrointestinal bleeding.12 Treat rhabdomyolysis aggressively with saline diuresis, alkalinization of the urine, and an infusion of 0.5 gm/kg of mannitol with or without furosemide.12 Treat seizures with benzodiazepines.12

Patients with minor heat-related illnesses may be safely discharged home after cooling. Instruct the patient to rest, drink plenty of fluids, and avoid the heat. Discuss with the patient the methods to remain cool if they are exposed to heat. This requires adequate rest, hydration before physical exertion, periods of rest during exertion when the individual can cool off, and adequate oral fluid intake during exertion. Arrange follow-up within 24 hours for a reevaluation.

Admission is required in several circumstances. Admit patients with heat exhaustion for 23 hour observation if they have abnormal vital signs, abnormal laboratory investigations, or if they remain symptomatic after fluid therapy. Admit all patients with heatstroke to an intensive care unit. Permanently altered and unstable thermoregulatory mechanisms in the survivors of heatstroke increase their susceptibility to future heat illness. Prevention through education should be a part of every discharge plan.

Further management of the heatstroke victim can be difficult, even after successful initial resuscitation and stabilization. Heatstroke is a multisystem insult that affects virtually every organ system. Neurologic complications of hyperthermia include seizures, cerebral edema, and localized brain hemorrhages. Irreversible brain damage often occurs above 42°C or 108°F. Cerebellar impairment may persist after recovery. Cardiac complications include tachyarrhythmias, high cardiac output heart failure, and myocardial infarction. Pulmonary edema may be cardiogenic in patients with a limited cardiac reserve or secondary to ARDS. Pulmonary aspiration can be encountered in obtunded patients. Acute renal failure may be due to direct heat damage, renal hypoperfusion, or rhabdomyolysis. Mucosal ulceration of the gastrointestinal tract is common and can lead to gastrointestinal hemorrhage. Liver damage and dysfunction are common. The extent of hepatic necrosis and cholestasis may not be apparent until 48 to 72 hours after the heat injury. Hematologic complications include hemolysis, thrombocytopenia, and disseminated intravascular coagulation. Megakaryocytes are especially sensitive to heat injury. Disseminated intravascular coagulation is triggered by diffuse endothelial and organ damage. Its onset is usually delayed 2 to 3 days and is associated with a high mortality.17,18

Complications can occur during the cooling of the hyperthermic patient. Discontinue all cooling techniques when the core body temperature reaches 39°C or 102°F. Continued cooling can result in hypothermia as the core temperature continues to decrease after cooling is discontinued. Monitor the patient to ensure that their core body temperature does not increase. The patient may experience muscle fasciculations, shivering, and shaking during the cooling process. These can be managed with intravenous benzodiazepines. Ice water immersion and ice packing make patient monitoring and management difficult if not impossible. Iced peritoneal lavage and iced gastric lavage are invasive procedures associated with significant potential complications. Refer to Chapters 58 and 66 regarding the complications associated with the placement of the peritoneal lavage catheter and the nasogastric tube, respectively.

The best intervention for heat-related illness is prevention. If caught early, heat illness responds to rest, exposure to shade and a breeze, and the ingestion of cool liquids. External evaporative cooling is acknowledged to be the safest means of cooling the hyperthermic patient. The tragedy of heatstroke is that it so frequently strikes highly motivated young individuals under the discipline of work, military training, or sporting endeavors. Heat-illness precautions should be implemented even in temperate zones during the hot summer months.