Description of event

A heat wave is defined in meteorological terms as a prolonged period of unusually hot weather. The duration and intensity of the heat play an important role in how people are affected. Illness tends to occur within 2 days of excessive heat. However, there are certain populations who are at increased risk and who may exhibit symptoms earlier. The elderly, children, infants under 1 year of age, persons with preexisting diseases, those taking various drugs and medications, and urban dwellers are more susceptible to heat-related illness. Prolonged exposure to heat can exacerbate preexisting chronic conditions, including various respiratory, cerebral, and cardiovascular diseases. Heat waves have a greater observable effect on respiratory mortality than on cardiovascular mortality, but the underling mechanisms remain unclear. Risk factors for serious heat-related injury are outlined in Box 99-1 . ^,

Each year, an average of about 700 people die from heat-related illnesses in the United States, with greater mortality during heat wave events. The Centers for Disease Control and Prevention estimated that from 1999 to 2009 there were about 7000 U.S. deaths attributable to extreme heat. There were 600 deaths during the Chicago Heat Wave of July 1995. The next summer, during the 1996 Summer Olympics in Atlanta, Georgia, 1059 people were treated for heat-related illness. During summer 2003, Europe experienced one of the worst heat waves in history, with an estimated mortality between 25,000 and 70,000 deaths in Western Europe. A 2010 heat wave in Moscow, Russia, which lasted 44 days, became a public health crisis when it caused major wildfires and resulted in 11,000 deaths. ^,

The human body is able to dissipate heat by four mechanisms. Radiation is the passive transfer of heat by electromagnetic waves. This accounts for 65% of heat transfer. Evaporation is the transition of liquid into gas. This only occurs when the outside temperature reaches 95 °F, and it accounts for 30% of heat transfer. Convection is heat loss to air and water vapor molecules surrounding the body, and it accounts for 10% of heat transfer. Finally, conduction is heat transfer via direct physical contact. It is only responsible for 2% of heat transfer.

Heat waves are among the most common emergencies and are the leading environmental cause of death in the United States, followed by cold-related deaths during winter months. Within the twenty-first century, exposure to heat is expected to increase as the average global temperature rises at least 3 °F. Moreover, climate change is expected to increase the frequency and severity of heat waves. Given the projected increase in global prevalence of chronic respiratory and cardiovascular disease and the aging of the U.S. population, an increased proportion of the population will be susceptible to heat-related morbidity. Heat wave mortality risk is ultimately influenced by multiple factors, including intensity and duration of heat, physical acclimatization of various communities, community preparation such as heat wave warning systems, and public willingness to take protective measures.

Pre-Incident actions

The most important action in preventing illness during a heat wave is proper preparation and public education before the heat wave begins. Proactive heat wave response plans are crucial in reducing heat-related morbidity, and many states have developed their own effective interventions to heat wave events. One should identify vulnerable populations (e.g., the elderly, socially isolated, chronically ill, mentally ill, or homeless) and target interventions to those most at risk. Interventions should include staying cool, hydrated, and informed about heat alerts in the area, as well as remaining cognizant of symptoms of heat illness. Some states have launched campaigns encouraging residents to check on their at-risk neighbors, whereas other efforts have included enlisting local students or the National Guard to participate in home visits. Utility companies should be represented in emergency operations centers to work with states in prioritizing power restoration to vulnerable populations. Multiple media formats, including press releases, social media, calls, and web updates, should be used to disseminate up-to-date information about resources.

Educating the public allows people to protect themselves from excessive heat exposure. People should reduce strenuous activity or reschedule outdoor activities until the coolest time of day. They should wear lightweight clothing and light colors, and avoid restrictive hats that will block sweating and evaporation of heat. They should drink large amounts of water or other nonalcoholic beverages while avoiding alcohol intake. They should know the forecasted temperature and continuously monitor their dwelling’s indoor temperature in case cooling systems fail. Finally, people should spend as much time as possible in air-conditioning and avoid direct sun exposure.

Hospitals and emergency departments should be prepared for an influx of patients presenting with heat-related illnesses. Administrators should consider activating their emergency operations center, and should ensure that staffing and resources are adequate. Heat waves are associated with higher levels of emergency medical services (EMS) activity and may require a coordinated regional disaster response. Emergency medicine providers are engaged at a regional and national level, through Disaster Medical Assistance Team (DMAT) deployments, and in triage and care for evacuated patients.

Post-Incident actions

In the prehospital setting, remove the patient from the heat. Disrobe the patient and apply ice packs to the neck, axilla, and groin. If a prehospital medical tent is immediately available, a patient should be cooled to under 104 °F (40 °C) before transport, as every minute of hyperthermia increases morbidity. Otherwise, transfer to an emergency department should be made rapidly. Intravenous (IV) fluid should be started, and blood sugar should be measured.

Always assess vital functions and obtain an accurate core temperature with a rectal probe. Temperature, neurologic status, and vital signs should be monitored continuously. Laboratory evaluation should include a complete blood count, electrolyte and lactate levels, and a urinalysis. Hyponatremia or hypernatremia can occur depending on the patient’s salt and water balance. Acute renal failure and myoglobinuria may be present with rhabdomyolysis. If heat stroke is suspected, liver function tests and coagulation studies are needed to assess for hepatic necrosis or disseminated intravascular coagulation.

Further diagnostic tests should include an electrocardiogram, computed tomography of the head for patients with undifferentiated altered mental status, and a chest x-ray in cases of respiratory distress.