Heat-Related Illnesses
SUMMARY:
Climate change is causing unprecedented extreme heat events throughout the globe, with greater shares of the world population exposed to dangerous levels of heat. Critical heat waves are predicted to occur with greater frequency in the next few decades as the earth’s atmosphere continues to warm to previously unseen levels. This extreme heat has led to an increase in heat-related illnesses and deaths, as well as exacerbations of heat-sensitive conditions. Heat-related illnesses are preventable, and prompt recognition and treatment can decrease morbidity and mortality.
General Principles
- Heat-related illness incidence has been on the rise
- In the past 20 years, there has been a 54% increase in heat-related mortality among persons > 65 years of age
- The clinical presentation of heat-related illnesses varies depending on severity
- Mild to moderate heat related illnesses can generally be treated in clinic or at home
- Severe heat related illness requires prompt treatment in a hospital setting
- Heat-related illnesses can be present in the absence of a heat wave and clinicians should have a high index of suspicion for diagnosis
- Clinicians can help identify patients at risk for heat-related illnesses and counsel them prior to the hotter seasons on methods to stay cool
- Use of evaporative coolers | Heat pumps | Air conditioning | Fans
- Check a weather app for the heat index and adjust outdoor exposure on hot days
- Increased water intake on hot days
- Develop a heat plan for hot days (e.g., Plan to seek shelter)
- If able, have a social worker check on patients at risk for heat-related illnesses
Risk Factors
- Susceptibility to heat-related illnesses is dependent on individual patient, societal and environmental factors
- Individual susceptibility
- Age (e.g., Older than 65 years | Infants | Young children
- Pregnant people
- Outdoor workers | Athletes
- Pre-existing medical conditions (e.g., Cardiac disease | Kidney disease| Obesity | Disabilities
- Social isolation | Immobility |
- Medications (e.g., Diuretics | Anticholinergics | Weight loss supplements) | Drugs (e.g., Cocaine | Amphetamines) | Alcohol
- Heat exposure
- Humidity | Indoor heat sources | Lack of access to cooling | Heat amplification (e.g., Concrete spaces)
- Sociocultural factors
- Poverty
- Structural and environmental racism (e.g., Urban heat islands due to history of red lining neighborhoods)
- Housing status | Literacy
- Limited worker protections
Mild Heat-Related Illness
Heat rash
- Inflammatory disorder of the epidermis due to blockage of sweat glands
- May develop superimposed bacterial infection
- Treatment
- Remove patient’s clothing
- Evaporative cooling (e.g., Fanning + Misting)
- Topical glucocorticoids | Topical antibiotics
- Avoid topical emollients which may further occlude sweat glands
- Advise patient to wear loose clothing and avoid hot environments
Heat cramps
- Painful muscle cramps and spasms throughout the body
- Typically occurs during or following activity in the heat
- Results from excess loss of salt from sweating
- Treatment
- Remove patient from heat | Rest
- Oral hydration that includes electrolytes
Heat edema
- Swelling of the limbs due to the physiologic compensatory mechanism of peripheral vasodilation in the setting of heat exposure
- Treatment
- Elevated lower extremities | Remove patient from heat
- No indication for diuretics
Heat syncope
- Brief loss of consciousness due to pooling of blood in extremities from heat edema
- Treatment
- Remove patient from heat | Rest in a supine position
- Passive cooling (e.g., Air conditioning | Fans | Remove clothes)
- Oral or IV rehydration
- Monitor mental status
- If no clinical improvement with above, or if concern for cardiac cause of syncope, then further work up is necessary
Sunburns/Thermal Burns
- Sunburns occur following sun exposure, generally after 4 hours
- Symptoms include: Erythema | Warm and tender skin | Swelling
- More serious sunburns can lead to: Blistering | Headaches | Fever | Fatigue | Nausea
- Thermal burns are a serious skin injury caused by contact with excessively high heat sources
- Serious burns require admission to the hospital for wound care and IV hydration
Moderated Heat-Related Illness
Heat exhaustion
- Caused by a decrease in body water content or blood volume due to excessive salt and/or fluid losses in the setting of heat exposure
- Body temperature may be mildly elevated (< 40°C)
- Characterized by: Profound fatigue | Weakness | Headache | Dizziness | Nausea/vomiting
- Notably, no changes in mental status or neurologic symptoms
- Lack of neurologic changes helps differentiate heat exhaustion from heat stroke
- Treatment
- Remove patient from heat | Rest in supine position
- Evaporative cooling
- Intravenous or oral rehydration
- Monitor mental status
- If no clinical improvement with above, then consider further work up and possible hospital-based treatment
Severe Heat-Related Illness
Heat Stroke
- Medical emergency that requires prompt diagnosis and treatment
- Take complete history
- Check core body temperature
- Presentation classically composed of a triad of signs and symptoms:
- Hyperthermia (e.g., Internal temperature > 40°C) | Neurologic changes | Recent exposures to hot weather and/or physical exertion
- Neurologic changes and an elevated core body temperature help differentiate heat stroke from heat exhaustion
- Other common signs: Tachycardia | Tachypnea | Hypotension
- Two categories of heat stroke
- Classic heat stroke: More common in patients during a heat wave with pre-existing conditions | Mortality nearly 80% if untreated
- Exertional: Healthy patients who preform demanding tasks | Mortality 33% if untreated
- Hot and dry skin a feature of classic heat stroke
- Sweating is more common in exertional heat stroke
- Severe neurologic symptoms may occur such as: Seizures | Incontinence
- Presents in three phases:
- Acute phase: Hyperthermic-neurologic
- Hematologic–enzymatic phase: Peaking 24 to 48 hours later | Inflammation | Coagulopathy
- Late hepatic–renal phase: Occurring ≥ 96 hours after symptom onset | Organ failure
- While treating for heat illness, consider differential diagnosis in these critically ill patients:
- Sepsis | Stroke | Toxicological emergencies (e.g., Serotonin syndrome | Anticholinergic toxidrome) | Endocrinologic emergencies (e.g., Thyroid storm)
- Treatment
- Move patient to cool environment and immediately work to lower body temperature
- Assess and manage: Airway | Breathing | Circulation
- Diagnostic tests: CBC | CMP | U/A | Urine Drug Screen | PT/PTT | CK | EKG CXR if any respiratory symptoms
- If outside of hospital setting: Pour copious amounts of cool water on patient | Use evaporative cooling
- Insider the hospital: Rapidly cool patient to 38°C to 39°C within 30 minutes of presentation
- Effective methods for cooling: Cold water/Ice water immersion (most effective) | Cold fluid infusion | Ice packs to neck, groin and axilla | Evaporative cooling
- Benzodiazepines may be used for: Agitation | Discomfort | Shivering
- Antipyretics are NOT recommended can worsen coagulopathy and end organ damage
- ICU admission is needed for management of end organ failure if present
KEY POINTS:
- Climate change has led to increasing extreme heat events and an increase in heat-related illness incidence and mortality
- Clinicians can help prevent heat-related illnesses by identifying and counseling high risk patients on strategies to stay cool
- Heat-related illnesses can range from mild, which can be treated at the home or office, to severe, which requires prompt hospital evaluation
- Treatment of heat-related illnesses generally relies on prompt cooling and hydration
Primary Sources – Learn More
NEJM: Treatment and Prevention of Heat-Related Illness
