Heat Illness

What is Heat Illness?

Hyperthermia, also known as heat-related injury or illness, exists on a range, marked by the body’s struggle to regulate its own temperature. This condition can show up in many different ways and vary in its level of severity. It can be harmless conditions like heat cramps or heat swelling, or it can be life-threatening like heatstroke. In this discussion, we will only focus on non-life-threatening heat-related illnesses.

It’s crucial to identify and manage these conditions correctly because moderate heat-related illnesses can become heat strokes, which are life-threatening. Consequently, it’s important that these injuries are taken into account by medical professionals when making their decisions, swiftly recognized, and treated correctly.

We’ll also go over the demographics, including those who are at high risk, warning signs in patient symptoms, available treatment options and strategies, and ways to prevent these conditions. All of these factors have significant roles in reducing the harm, fatalities, and healthcare costs associated with these types of injuries.

What Causes Heat Illness?

Humans are able to keep their body temperature within a certain range, typically between 97.7 to 99.5°F. Our bodies have ways to regulate and adjust to temperatures between approximately 95.0 to 105.8°F. Beyond this, our bodies struggle to cope with the heat. The temperature we maintain is a balance of the heat generated from metabolism, physical work, and interaction with our surroundings. Many factors can tip this balance, such as our hormone levels, the external temperature and humidity, and the level of air movement in our environment. This can result in a net change in our body temperature.

Our bodies exchange heat with their surroundings through evaporation, air flow, direct contact, and heat emissions. However, when the temperature and humidity in our surroundings increase, dissipation of heat by emission and contact is less effective. In such situations, evaporation – that is, the release of heat through sweating – becomes the main way for our bodies to cool down.

This entire process is coordinated by sensory receptors. Thermoreceptors, which are found in the skin, organs, and spinal cord send temperature information to a part of the brain known as the hypothalamus. Based on this information, the body can make physical and behavioral changes to help bring the body temperature back to normal. Physical changes include dilation of blood vessels – especially in the hands, feet, and face which are critical areas to cool down quickly. Other changes can include an increase in sweat production and a decrease in metabolism, leading to less internal heat production.

Behavioral changes are also triggered, but these are under our control. For instance, we might feel the need to find shade, use air conditioning or a fan, or to take off layers of clothing. Risk of overheating can increase when these instincts are ignored, for instance, when athletes train in hot conditions or when elderly individuals may not have access to air conditioning during heatwaves. Other factors like existing health conditions, changes in mental status, or certain medications can also limit a person’s ability to respond appropriately to hot conditions.

Risk Factors and Frequency for Heat Illness

Heat illness is a common health issue worldwide and is the leading cause of weather-related deaths, according to the National Oceanic and Atmospheric Administration and the Centers for Disease Control. Between 2001 and 2010 in the United States, over 28,000 hospitalizations due to heat illness were recorded from a network of 20 states. It was more common in males and individuals over 65 years.

The majority of these hospitalizations happened in Midwest and Southern states, likely due to consistently high temperatures in these areas. Similar trends have been observed globally. Men are generally more affected by heat illness, possibly due to their greater presence in manual labor jobs, which often involve working in hot and poorly ventilated environments.

Several factors contribute to the risk of developing a heat-related illness:

• High temperatures and humidity
• Heatwaves (temperatures above 90.0°F for at least three days)
• Old or young age
• Obesity
• Current infections
• Hydration levels
• Alcohol consumption
• Use of certain drugs (diuretics, anticholinergics, beta- or calcium-channel blockers, antihistamines, amphetamines)
• Existing medical conditions (diabetes, skin disorders, sickle cell trait, cardiovascular disease)

Apart from old people who have many of these risk factors, adolescents, and athletes are also more prone to heat-related injuries. For instance, heat illness is common among teenagers and children during summer due to outdoor activities and sports. Additionally, athletes face considerable risks of heat stroke, which is one of the biggest causes of death within this group. All these risks are amplified by heavy sweating that can cause significant sodium and chloride losses and lead to dehydration.

Younger children are especially at risk for heat-related injuries as they:

• Have a greater surface area relative to their body mass
• Have a lower blood volume
• Have less mature body temperature regulation mechanisms
• Sweat less and at higher temperatures
• Acclimatize to hot environments slower

You can reduce the risk of heat illness by addressing modifiable factors like obesity, alcohol use, certain medication use, dehydration, and avoiding strenuous activities in hot and humid conditions.

Signs and Symptoms of Heat Illness

Getting accurate information from the patient, their family, or first responders is crucial in understanding what the patient was doing when the symptoms started and where they were found. Heat illness symptoms can differ depending on the specific type of heat injury. Here are a few examples of various heat-related injuries:

• Heat edema: This refers to swelling and potential discomfort in the hands and feet due to the widening of blood vessels and body fluids gathering in the lower parts of the body due to gravity. An example might be an older individual who recently moved to a hotter climate and experiences swelling in their hands and feet after a couple of days.
• Heat rash: Also known as miliaria or prickly heat, this is caused by the blockage of sweat glands when exposed to hot climates. Wearing tight clothing or using items like bandages might worsen the condition. It includes three types:
  • Miliaria crystallina: involves the outer layer of skin and usually appears on the face and trunk as small, clear blisters. It can also occur during infancy.
  • Miliaria rubra: affects deeper skin layers and appears as small, red bumps usually on the neck and upper body. These can be itchy or feel like a burn. The onset is typically days to weeks after heat exposure.
  • Miliaria profunda: affects even deeper skin layers, resulting in larger, white blisters that are usually not painful.
• Heat cramps: involuntarily and intense muscle spasms during or after physical activity, often due to a deficiency of sodium, potassium, chloride, or magnesium. Additional symptoms may include nausea, vomiting, fatigue, weakness, sweating, and a rapid heart rate.
• Heat syncope: temporary dizziness, weakness, or fainting during prolonged standing or sudden movements in a hot environment. It’s thought to be caused by dehydration and low blood pressure.
• Heat stress or heat exhaustion: symptoms can include nausea, vomiting, dizziness, irritability, headache, thirst, weakness, excessive sweating, muscle cramps, and less urination when high body temperatures are present. Temperatures may not necessarily be high if associated with intense physical activity. If not addressed immediately, this condition can progress to life-threatening heatstroke.
• Heat injury: presents with similar symptoms as heat exhaustion, and can also include organ damage or dysfunction (like heart, kidney, liver or muscle injury).
• Central nervous system involvement: includes symptoms or signs that may include seizures, gait abnormalities, delirium, or coma. These signs should raise concern for heatstroke when body temperature is high.

Testing for Heat Illness

Sometimes, just by understanding your medical history and doing a physical examination, a doctor can diagnose if you are suffering from heat stress, heat injury, or even heat stroke. Often, you might appear completely normal on the typical medical tests. However, if your symptoms are concerning or severe, your doctor might feel the need to check your body temperature with a rectal thermometer, if possible.

Usually, unless your doctor is worried about imbalances in your body’s electrolytes (minerals that help your body function properly), severe dehydration, damage to your organs, or they’re considering other diagnoses, you won’t need extra tests. The severity of your symptoms could require further testing to avoid critical health problems, like severe heart conditions (cardiovascular collapse) that can happen when heatstroke progresses. If your symptoms don’t match heat-related issues, you might be referred for additional medical tests.

Some tests that your doctor might consider include a complete blood count (CBC) and clotting factors. These tests can indicate an intense response in your body, which can lead to a dangerous condition where the blood starts to clot too much (disseminated intravascular coagulation) in severe cases. You might also have your electrolyte and magnesium levels checked. This is to see if there are any abnormalities due to an imbalance in the fluids in your body – for instance, drinking lots of water but not taking in enough electrolytes.

Your doctor might also want to test your kidney and liver function, to assess for any possible damage due to severe heat illness. A test to measure creatinine kinase levels could help evaluate if there’s skeletal muscle injury or a condition characterized by rapid breakdown of muscle tissue (rhabdomyolysis). Urinalysis allows a further evaluation of kidney health and checks for certain proteins in the urine.

An electrocardiogram (EKG) may be performed to check for irregular heartbeats or arrhythmias since severe heat illness can trigger these or expose underlying heart conditions.

If you have severe heat illness, you may have low blood sugar levels, requiring carbohydrate replacement. And because decreased organ perfusion (meaning less blood is getting to your organs) can occur with severe heat illness, you may also have elevated lactic acid levels. In some very specific circumstances, you might need other tests like a lumbar puncture (a test where fluid is taken from your spine) or a CT scan of the head if your doctor is worried about other causes for your symptoms.

Treatment Options for Heat Illness

In simple terms, the first step in treating heat-related illnesses is to stop what you’re doing and move to a cool place; this helps in all situations because it starts the cooling process. Mild conditions like swelling (heat edema), fainting (syncope), rashes, and muscle cramps can generally be managed by just taking care of yourself.

However, in more severe situations, like heat exhaustion, you might need immediate medical attention to ensure your breathing and heart are functioning properly. If anything seems wrong, it might be necessary to go to a hospital for more intensive care. But if you’re generally alright, drinking water or a drink with electrolytes on-site would help you rehydrate. Research shows that drinking fluids through the mouth and getting them through an IV (a method doctors use to supply fluids directly into your body) work just as well in treating heat-related illnesses. But it’s important not to drink too much too fast, as this could also cause problems, especially for people with heart issues.

For treating specific conditions:

– Heat edema (swelling): Raising the swollen area and wearing tight-fitting garments can reduce the swelling. There’s no real need for water pills (diuretics) in this case.

– Heat rash: A key treatment step is to avoid wearing tight clothes. Applying soothing lotions like calamine or mild cortisone creams like triamcinolone 0.1% cream can help with discomfort and inflammation. If there’s a bacterial infection on top of the rash, you may need to apply an antibiotic cream; mupirocin is one common choice because it treats one of the most common types of bacteria we see in these infections, Staphylococci.

– Heat cramps: Stop any physical activity and start drinking fluids. Resting and gently stretching the cramping muscles can provide relief. Taking certain medicines, like diazepam, magnesium, or calcium, won’t help.

– Heat syncope (fainting): Besides drinking water or an electrolyte beverage, lying down with your legs elevated higher than your heart can help. Tracking your heartbeat when lying and standing (known as orthostatic readings) can be used to make sure your body is getting enough fluids and to see if your symptoms improve as you change positions.

– Heat stress or exhaustion: More proactive steps should be taken to cool down, such as misting lukewarm water over the skin and using a fan to evaporate it. If the symptoms are bad or injurious to the point where you’re unable to drink enough fluids, you might need an IV. If your electrolyte levels or other mineral balances are disturbed, these might need to be corrected too.

Medications to reduce fever or relax muscles are not necessary or helpful in heat-related illnesses.

If things get serious and you start showing symptoms of heatstroke, that needs much more extensive treatment not addressed in this article.

What else can Heat Illness be?

When doctors are trying to diagnose heat-related illnesses, they consider some other health conditions that could cause similar symptoms. These conditions include:

• Infections like tetanus, sepsis, or meningoencephalitis, which can also lead to changes in mental status, body temperature, and specific neurological signs.
• Primary metabolic abnormalities such as thyroid storms or diabetic ketoacidosis.
• Brain disorders, including stroke or seizures.
• Poisoning from drugs, including conditions like anticholinergic syndrome, neuroleptic malignant syndrome, serotonin syndrome, and withdrawal symptoms.

On the other hand, symptoms of certain heat-related illnesses can also resemble other syndromes. For example, the swelling from heat edema shouldn’t be confused with swelling from heart failure, liver dysfunction, or a blood clot in a deep vein. Similarly, heat fainting should not be mistaken for fainting caused by other reasons such as heart-related, a sudden change in consciousness due to medical conditions like a lung clot, ruptured ectopic pregnancy, a tear in the aorta, or exposure to certain environmental gases.

What to expect with Heat Illness

The outlook is very good for the less severe heat-related illnesses mentioned above. They tend to resolve on their own when the person is moved out of the hot environment and provided with care like drinking water or sports drinks to rehydrate and replace lost salts in the body.

Possible Complications When Diagnosed with Heat Illness

Minor heat-related illnesses are generally harmless and don’t lead to any future problems. However, more severe forms, such as heat exhaustion, heat stress, and heat injury, can lead to complications which are worsened by factors such as the patient’s age, existing health conditions, any organ damage, or severe electrolyte imbalances. These patients might need to be admitted to a specialist hospital for further stabilization before they can go home. Some factors that might indicate a need for hospitalization could include being over 65 years of age, high body temperature, changes in mental awareness, and increased creatinine levels from the standard range.

Main Points:

• Minor heat illnesses are harmless and don’t lead to future problems.
• Severe heat-related illnesses can lead to complications worsened by the patient’s age, existing health conditions, organ damage, or severe electrolyte imbalances.
• Patients with severe heat illnesses might need to be admitted to a specialist hospital for stabilization before being discharged.
• Predictors of hospitalization can include being over 65 years old, high body temperature, mental changes, and increased creatinine levels.

Preventing Heat Illness

Teaching the general public about how to avoid heat illness should be a priority. This includes emphasizing the need to stay cool on hot days and to seek shade whenever possible. One good way to gauge the risk of heat illness is by using a measure called the wet-bulb globe temperature (WBGT) index, which takes into account temperature, humidity, and sunlight. If the WBGT index is not available, the heat index, which looks at temperature and humidity, can be used instead, although it’s not quite as accurate.

There are also tools that can be used to gauge an individual or a group’s vulnerability to heat illness, although experts disagree about how effective these are. Some other strategies for avoiding heat illness include using air conditioning, taking breaks in cool or shaded spots on hot days, and not overexerting oneself during the hottest parts of the day.

Getting used to the heat gradually in the days or weeks before exerting oneself in a hot place or at a hot time of day is one of the best ways to avoid heat illness. It’s generally recommended to take 7 to 14 days to acclimate, although this may need to be maintained over 2 to 3 weeks to prevent the benefits from fading away. Staying properly hydrated is also crucial in a hot environment. For instance, one suggestion for teenagers is to drink 240 mL (8 ounces) of fluid for each pound they lose through exercise.