Heatstroke, or sunstroke, is the most severe heat-related illness and a fast-developing medical emergency. If left untreated, it can lead to rapid and severe damage to the brain, heart, kidneys, muscles, and even death.
Heatstroke typically develops after milder heat-related illnesses like heat cramps, fainting, and heat exhaustion. If one can cool down within 30 minutes, these milder conditions don’t require emergency medical care. However, heatstroke can occur suddenly or gradually, even without prior signs of heat injury.
Between 2004 and 2018, the United States witnessed an average of 702 heat-related fatalities each year. Among these, over half were directly attributed to heat.
What Are the Types of Heatstroke?
Heatstrokes are classified into two categories based on whether exertion is present: exertional and nonexertional heatstroke.1. Exertional
Exertional heatstroke primarily affects young and healthy individuals who engage in vigorous activities, such as sports, laborious work, or military training, in hot and/or humid environments.Sometimes, exertional heatstroke can even take place without a hot environment.
Unfortunately, those affected by exertional heatstroke are often less concerned about the potential impacts of heat on their health, leading to early symptoms being ignored or dismissed. In addition, people suffering from exertional heatstroke are typically younger and/or healthier than those suffering from nonexertional.
Under intensive care, exertional heat stroke has a mortality rate of 26.5 percent.
2. Nonexertional
Nonexertional heatstroke, also known as classic heatstroke, typically occurs in people who have difficulty regulating their body temperature, such as older individuals, young children, or those with chronic illnesses. Unlike exertional heatstroke, this type can take several days to develop.Related Stories
7/25/2021
In this case, even without intense physical activity, exposure to high temperatures in the surrounding environment can trigger heatstroke, with comorbidities such as obesity, diabetes, hypertension, heart disease, renal disease, dementia, and alcoholism.
Under intensive care, the mortality rate of classic heatstroke is 63.2 percent, higher than that of exertional heatstroke. This is because, in the case of exertional heatstroke, the individual typically ceases activities once the signs are noticed. Sometimes they are forced to stop, as their physical conditions (e.g., having fainted) no longer allow them to continue. However, in the case of nonexertional heatstroke, an individual's condition continues to deteriorate until medical help is received.
What Are the Symptoms and Early Signs of Heatstroke?
Currently, there are two sets of heatstroke criteria being used worldwide.According to the Bouchama heatstroke criteria, heatstroke occurs when the core body temperature exceeds 40 C (104 F), accompanied by dry skin and central nervous system abnormalities. This popular definition has been employed in clinical settings.
However, older patients often do not present with severe temperature elevation, and the Bouchama definition doesn’t include other organ damage markers. Therefore, the Japanese Association for Acute Medicine (JAAM) introduced its own heatstroke criteria that include components covering renal and hepatic complications and other factors but don’t have temperature as one criterion.
Since heat exhaustion is usually a precursor to heatstroke, and its symptoms are among those of heatstroke, with a minor exception, the signs of heat exhaustion can warn of impending heatstroke.
Symptoms of Heat Exhaustion and Heatstroke
Heat exhaustion has the following symptoms:- Increased heart rate or breathing.
- Throbbing headache.
- Lightheadedness.
- Mild disorientation/sense of confusion.
- Excessive thirst.
- Muscle weakness or cramps.
- Irritability.
- Nausea or vomiting.
- Pallor (pale skin).
- Profuse sweating.
- Fainting or loss of consciousness.
- Feverish body temperature.
- Fatigue.
- Decreased urinary output.
Additional Symptoms of Heatstroke
Heatstroke can share the same symptoms as heat exhaustion. However, classic heatstroke typically exhibits reduced or no sweating, whereas exertional heatstroke is characterized by sweating.When heat exhaustion develops into heatstroke, the patient’s mental condition also worsens, which can help differentiate heat exhaustion from heatstroke.
Additional heat stroke symptoms include the following:
- Extremely high body temperature: Core body temperature can reach 104 F (40 C) or higher.
- Reddened skin: This is due to elevated body temperature.
- Altered mental state or behavior: Besides confusion and irritability, the patient may experience slurred speech, agitation, severe restlessness, difficulty concentrating, hallucinations, and delirium.
- Seizures: The brain may get damaged when the body shakes uncontrollably for a prolonged period.
- Coma: Loss of consciousness can occur in both heat exhaustion and heatstroke.
- Lack of sweating: This is a sign the body no longer responds normally to sweat to cool itself, thus resulting in overheating.
- Sudden, extreme exhaustion: The patient can suddenly feel weak and tired.
- Dry, swollen tongue: Heatstroke can cause a person's tongue to swell and become dry.
What Are the First Aid Measures to Treat Heatstroke?
If someone shows signs of heatstroke, notably a high body temperature above 104 F (40 C), call 911. While waiting for help to arrive, take the following actions to cool the overheated individual:- Move the person to a shaded, well-ventilated area or indoors.
- Remove excess clothing.
- Cool the person immediately by:
- Giving him or her a cold water bath, which can also be safely done for older people (while monitoring their blood pressure and body temperature to avoid overcooling), until the body temperature drops below 100.4 F (38 C).
- Providing CPR, if needed.
- Spraying the person with a hose if a cold water bath is not possible.
- Placing ice packs or cold, wet cloths/sponges on the body, including the head, neck, armpits, back, and groin area. Cooling these areas can reduce body temperature, as they all have blood vessels near the skin’s surface.
- Fanning the person.
- If the person is fully conscious, offer half a glass of cool water (pdf) to drink slowly every 15 minutes. Avoid liquids with alcohol or caffeine. Sports drinks are also good choices, as they contain water and electrolytes.
- Stay with the person until medical professionals arrive.
What Are the Main Causes of Heatstroke?
Heatstroke occurs when the body’s temperature regulation system fails, usually in combination with dehydration and factors such as excessive metabolic heat production (from exertion), extreme environmental heat, and inadequate or impaired heat dissipation. This causes the body temperature to rise rapidly, rendering the sweating mechanism ineffective. As a result, the body becomes overwhelmed by heat and unable to cool down, which causes inflammation that harms cells.
According to a review article published in The New England Journal of Medicine (NEJM), the heatstroke-related inflammatory response is similar to a condition called systemic inflammatory response syndrome, which can lead to serious complications, such as disseminated intravascular coagulation, multiorgan failure, and even death. Reduced blood flow to the intestines during heatstroke can damage cell walls and cause toxins and possibly harmful substances to enter the bloodstream, leading to endotoxemia.
Since our bodies generate a large amount of internal heat, we rely on the hypothalamus to regulate our temperature, keeping it at around 98.6 F (37 C).
In both exertional and classic heatstroke, the following factors can contribute:
- Wearing excessive or excessively tight clothing, hindering sweat evaporation and body cooling. Sweating can account for up to 90 percent of the body’s heat reduction efforts.
- Becoming dehydrated by not drinking enough water to replace fluids lost through sweating.
- Staying in a humid and/or poorly ventilated place, where humidity reduces the body’s ability to cool down by sweating.
- Consuming alcohol, which can interfere with your body's thermoregulation.
- Getting sunburned.
- Taking medication. Side effects of certain drugs can make people prone to dehydration or raise their body temperature.
In the summer, the temperature within a car parked outside can rise by 20 degrees within 10 minutes and a staggering 40 degrees within an hour, even if the weather doesn’t seem very hot. In a phenomenon called forgotten baby syndrome, an adult may unwittingly leave a child in a car, resulting in the child experiencing heatstroke or dying.
What Are the Phases of Heatstroke?
According to the NEJM review, heatstroke typically exhibits three phases, more distinct in exertional heatstroke than in classic:- Hyperthermic-neurologic acute phase: This phase rapidly increases body temperature and neurological symptoms.
- Hematologic-enzymatic phase: This phase peaks 24 to 48 hours after the event and involves changes in blood parameters and enzyme levels. Multiorgan system dysfunction and failure may peak during this phase.
- Late renal-hepatic phase: If clinical symptoms persist for 96 hours or longer, this phase may occur and affect the kidneys and liver.
Who Is More Likely to Develop Heatstroke?
Anyone can develop heatstroke, but the following groups of people are at a higher risk:- People aged 60 years or older whose central nervous system has deteriorated and can no longer regulate body temperature sufficiently.
- People who live alone or are socially isolated/homeless.
- Pregnant or breastfeeding mothers, who tend to have higher body temperatures.
- Infants and young children whose central nervous system hasn’t fully developed and who have a low sweating rate.
- Males. Men are more prone to heatstroke than women, but not other heat-related illnesses.
- People who previously experienced heatstroke.
- Overweight or obese people, whose bodies generate more internal heat than average.
- Sleep-deprived individuals, as sleep deprivation can decrease sweating.
- Individuals with restricted mobility, such as those who are bedridden or require support in daily activities, and people with sensory or cognitive challenges.
- People who work outdoors, such as construction workers and laborers.
- People with chronic illnesses, such as diabetes, cystic fibrosis, and respiratory illness; mental disorders (e.g., schizophrenia and depression); or substance (e.g., cocaine, heroin, and ecstasy) abuse problems.
- People who take certain medications that can make them prone to dehydration (e.g., diuretics, drugs for acute and chronic renal disease and hyperglycemia) or high body temperature (e.g., penicillins, anti-tuberculars, quinidine, and phenytoin).
- People experiencing sudden hot weather, such as a heat wave.
- People living in a poorly-ventilated home without air conditioning.
- People who don’t drink enough water.
- People who drink excessive alcohol.
- People living in cities. These individuals are susceptible to the urban heat island effect, where cities and metropolitan areas tend to be hotter than nearby rural and suburban regions. This is due to concrete buildings’ ability to absorb heat during the day and slowly release it at night, leading to elevated nighttime temperatures.
- Athletes, soldiers, and physically active people under increased physical strain are susceptible to exertional heatstroke, especially if they are overly motivated or pressured by coaches and/or teammates.
- Firefighters and people who work in hot environments and wear bulky or heavy clothing (e.g., firefighting gear, mascot costumes, personal protective equipment).
What Are the Tests to Detect Heatstroke?
Heatstroke diagnosis is typically conducted by health care providers in the emergency department. They carefully assess the patient’s symptoms, conduct a physical examination, and measure his or her rectal temperature (considered the most accurate) to detect any other potential causes of elevated temperature to rule out other medical conditions.To further evaluate the condition, confirm the diagnosis, and/or assess organ damage, health care providers may request specific tests:
- A complete blood count (CBC), or a full blood count (FBC), is a specific type of blood test that provides valuable information about the cells in a person’s blood. The test measures the levels of white blood cells, red blood cells, and platelets in the blood. It evaluates the patient’s oxygen-carrying capacity by analyzing red blood cell indices, hemoglobin, and hematocrit.
- A blood gas analysis is a widely used diagnostic tool that evaluates the levels of gases and acid-base content in the blood. The blood gas test provides crucial information about the partial pressures of oxygen and carbon dioxide in the blood, thus providing insights into the patient’s oxygenation and ventilation status (essential for assessing respiratory function). It is also beneficial in critical illness to measure the blood's acidity and, thus, the body's metabolic stability.
- A serum sodium test measures sodium concentration in the blood, which must be maintained near normal to avoid damaging effects on the central nervous system. Sodium is an essential electrolyte that helps regulate fluid balance, nerve function, and muscle contractions.
- A serum potassium test measures the level of potassium in the blood serum. Potassium is a vital mineral that facilitates nerve and muscle communication, aids in cellular nutrient exchange, and ensures healthy heart function. This standard test is used to be sure that safe levels of the electrolyte are maintained. Potassium levels may be influenced by intake and by kidney malfunction. Dehydration and heatstroke may put a lot of stress on the kidneys.
- Prothrombin time (PT) and partial thromboplastin time (PTT) tests are two clotting studies that may indicate that a severe complication—disseminated intravascular coagulation—has begun. This often accompanies multiorgan failure.
- A creatine kinase test, also known as a creatine phosphokinase test, is a blood test that measures an enzyme found predominantly in muscle cells, including skeletal and heart muscles and brain tissues. Levels are elevated in skeletal muscle injury and rhabdomyolysis, a medical condition characterized by the breakdown of muscle tissue, leading to the release of creatine kinase and myoglobin, a muscle protein, into the bloodstream. The precipitation of myoglobin in the kidney can lead to acute kidney injury.
- A urinalysis, also known as a urine test, is obtained to check for infection, glucose, and kidney filtering problems, and myoglobin to evaluate possible rhabdomyolysis in heatstroke.
- A computed tomography (CT) scan of the head is conducted in most cases when a patient is experiencing confusion to exclude the presence of other treatable brain conditions or central nervous system injury.
- A magnetic resonance imaging (MRI) scan may be conducted for patients experiencing ongoing neurological symptoms to assess small-vessel lesions caused by ischemia or hemorrhage and identify cytotoxic edema associated with irreversible neuronal damage.
- A chest X-ray may be performed if there are specific respiratory symptoms or concerns about potential complications related to heatstroke.
- An electrocardiogram (EKG) test is an easy and painless procedure that can monitor the electrical activity in the heart, as heatstroke can sometimes cause abnormal heart rhythms or reveal existing heart rhythm issues that might need specialized medical attention.
- A lumbar puncture, also known as a spinal tap, is a medical procedure used to collect a sample of cerebrospinal fluid from the space around the spinal cord. It can rule out other causes of a high body temperature.
What Are the Complications of Heatstroke?
Prompt treatment can lead to milder clinical signs, and most patients recover from any stage of a heat emergency without lasting effects within a few days. The prognosis worsens when kidney and liver dysfunction last over 96 hours.Autopsy studies indicate that end-organ failure after heatstroke is primarily due to heat-induced cell death, microclotting, hemorrhage, and inflammatory injury. Some neurological sequelae may persist for several weeks to months. According to one study, there is a higher mortality risk in individuals who had prior hospitalization for heat illness.
Depending on how long the body temperature remains high, heatstroke can result in many complications, including the following:
- Coma.
- Acute respiratory distress syndrome (ARDS).
- Swelling and possible permanent damage to the brain (e.g., cerebellar atrophy) and other vital organs.
- Kidney and/or liver failure.
- Congestive heart failure.
- Irregular heartbeats.
- Nerve damage.
- Circulatory problems (e.g., reduced blood flow to the heart).
- Rhabdomyolysis.
- Acute respiratory distress syndrome.
- Anterograde amnesia.
- Cognitive disorders.
- Disseminated intravascular coagulation.
- Metabolic dysfunction.
- Compartment syndrome (very rare).
What Are the Treatments for Heatstroke?
Out of the three phases of heatstroke, the most important for primary care practitioners is the acute phase, as swift recognition and treatment during this stage can be life-saving.1. Cooling Methods
In clinical settings, treating heatstroke involves quickly cooling the body through mechanical means, accompanied by standard resuscitation procedures. As prognosis worsens when core body temperature remains high, cooling efforts can be delayed only by essential cardiopulmonary resuscitation (CPR). Common cooling methods include the following:- Cold water immersion: This method is considered the most effective, although it’s uncomfortable for the patient. Studies have shown that cold water immersion can achieve a typical cooling rate of about 32 F (0.2 C) per minute in exertional heatstroke.
- Water pouring: When cold water immersion is unavailable, cold water can also be poured on the person while fanning him or her.
- Cool air blowing: An electric fan can help cool the person.
- Cooling sheets/blankets: Medical staff can wrap the patient loosely in cooling or wet sheets.
- Ice packs: Medical staff can place ice packs on the patient’s neck, groin, back, and armpits. This method is well-tolerated by older patients.
- Cold water lavage: This treatment involves using thin, flexible tubes called catheters to fill body cavities with cold water, helping reduce the body’s overall temperature. The catheter may be inserted into the rectum, bladder, or down the throat for this purpose.
- Cardiopulmonary bypass: In extremely severe cases, the individual's blood is rerouted from the heart and lungs to a collection machine. There, it is cooled before being returned to the body. However, this method requires highly trained personnel and advanced equipment.
- Evaporative and convective cooling: This combination of methods uses cool water spray or cold compresses along with continuous airflow over the body, such as a fan or air conditioning unit, to achieve cooling rates up to nearly 33 F (0.31 C) per minute. This method is also well-tolerated by older patients.
- Cooled intravenous fluids: These are administered through a vein in the patient’s arm.
Unfortunately, pharmacologic agents cannot be used, as they cannot speed up cooling. Anti-pyretic drugs such as aspirin and acetaminophen are ineffective since heat-related illness increases the body temperature through a different pathway than a typical fever. Additionally, these drugs can worsen coagulopathy and liver injury in heatstroke patients.
2. Rehydration
Hydration is also essential when cooling the patient. Once the patient is in the hospital, the medical staff will rehydrate him or her with an IV to compensate for fluid or electrolyte loss.If fully conscious, the patient can also drink water and/or sports drinks to rehydrate.
3. Medication and Oxygen
During and after the cooling treatment, doctors may give the patient the following:- Benzodiazepine to stop shivering/seizures during the cooling treatments, as shivering/seizures generate internal heat.
- Supplemental oxygen.
- Antibiotics. According to an animal study, administering nonabsorbable oral antibiotics, a laxative, and an enema before the onset of heat stress improved mortality rates from heatstroke. Antibiotics may help decrease the amount of toxins released from intestinal bacteria through the heat-damaged bowel wall. Further studies are needed to know if this is helpful in patients presenting after the onset of heatstroke.
4. Therapies
Once the patient’s body temperature is reduced and doctors discontinue the cooling treatments, immediate intervention with symptomatic support of organ functions should be the standard of care while being mindful of the potential development of systemic inflammatory response syndrome (SIRS).Unfortunately, as of the late 2010s, limited therapeutic options are available for managing organ dysfunction. Currently, several new treatment approaches are being tested.
To treat the following organ dysfunctions or failures, doctors use the following therapies:
- Artificial liver support therapy: In one Japanese case, a patient experienced ongoing consciousness issues, leading to the application of continuous electroencephalogram (EEG) monitoring, which identified hepatic failure as the underlying cause. The patient was treated with artificial liver support therapy, which improved his condition.
- Anticoagulation therapy: A near-fatal heatstroke patient suffering from multiple organ failure and disseminated intravascular coagulation was treated with cooling, aggressive volume resuscitation, anticoagulation therapy (with type 3 anti-thrombin), and steroids. He later fully recovered with no lingering health issues.
- Blood purification therapy: In one case, five classical heatstroke patients exhibited rapid progression of multiple organ dysfunction syndrome (MODS). Three received blood purification therapy alongside conventional treatment, while the others only received conventional treatment. The first three recovered, while the others soon died, suggesting that the blood purification therapy might have led to more favorable outcomes, possibly by removing proinflammatory cytokines associated with heatstroke from the blood.
- Fasciotomy: In cases of compartment syndrome (an increase in pressure within a closed muscle compartment that hinders blood flow), doctors can perform a surgical procedure called fasciotomy, which involves the cutting of the fascia (i.e., thick layers of connective tissue that enclose muscle compartments) to alleviate pressure within the muscle.
- Vasopressor and inotropic support: In cases of heart failure, intravenous administration of dobutamine, milrinone, or epinephrine may be considered. For severe multiorgan failure, extracorporeal membrane oxygenation (ECMO) may be utilized as necessary.
How Does Mindset Affect Heatstroke?
Studies indicate that the mindset or expectations of healing can significantly affect the body’s biological systems, similar to the response seen with placebos, whose effectiveness is primarily influenced by the patient’s belief that they are effective. Therefore, positive mindsets may enhance the effectiveness of actual medications and treatments. While there is no concrete evidence positive attitude impacts the prognosis of heatstroke, evidence supporting optimism in other illnesses suggests it is likely more effective than pessimism.How Can I Prevent Heatstroke?
Although potentially fatal, heatstroke is a predictable and preventable illness. You can take the following steps to prevent heatstroke, especially during hot weather:- In sweltering weather, try to stay indoors when possible.
- When it gets hot indoors, close your blinds or curtains and use an electric fan or air conditioning.
- If air conditioning doesn’t work at home, you can go to an air-conditioned mall, movie theater, or library.
- If you have to remain outdoors, stay in a shaded area.
- Schedule vigorous activities and sports during cooler times of the day to avoid the peak heat.
- Protect yourself from the sun by using sunscreen, wearing a wide-brimmed hat, or using an umbrella for shade.
- Take frequent drink breaks during outdoor activities and use a spray bottle to mist yourself to prevent overheating.
- Gradually increase your time outdoors to allow your body to adjust to the heat.
- Stay hydrated by drinking plenty of fluids, particularly water, slightly salted water, broth, and sports drinks. Avoid soft drinks and alcohol, as they can dehydrate you. Also, avoid drinking very cold fluids, as they may give you stomach cramps.
- Eat smaller meals and meals that don’t require cooking.
- Choose lightweight, loose-fitting clothing made with breathable fabrics and in light colors to help you stay cool.
- Take cool showers when you feel like it.
- Check with your doctors to see if any of your medications may reduce your body’s ability to dissipate heat.
- Never leave anyone (especially children and seniors) in closed cars on warm or sunny days, as temperatures can quickly become dangerously high inside the vehicle. This is still the case even if windows are slightly open. Also, remember to lock a parked car, so no children can get inside it and become trapped.
- Remember to check on older, sick, and frail family members, friends, and neighbors who might need assistance dealing with the heat.
- Know the symptoms of heat-related illnesses to help yourself and others stay safe.
- Check the reported heat index, which combines air temperature and relative humidity to estimate how hot it feels to the human body. When the relative humidity is 60 percent or higher, it prevents sweat from evaporating effectively, impairing your body's natural cooling process.
- Remember that exposure to full sunshine can elevate the reported heat index by 15 degrees. An alternative measure used mainly in Canada is humidex.
- Drink 5 to 10 ounces (150 to 300 milliliters) of water every 15 to 20 minutes while exercising.
- Wear light-colored clothing made from breathable material.
- Exercise in an indoor gym.
- Pay attention to hydration when doing aquatic exercises.
- Increase the exercise intensity gradually to let your body get accustomed to the temperature.
