The poor, older adults most vulnerable to heat-related illness
The Chicago heat wave of 1995 — the deadliest in U.S. history — killed nearly 750 people. Most were older, sick and lived in the poorest sections of the city, with no escape from their stifling, upper story apartments. Even those who made it to overwhelmed emergency departments (EDs) didn't always fare well. Four patients with cardiac problems died of heatstroke while waiting to be examined in the sweltering halls of Cook County Hospital.
Heat exhaustion and heatstroke lie on a continuum of heat-related illnesses that occur when the body's thermoregulatory responses fail to preserve normal core temperature. Heat exhaustion is milder, and usually causes nonspecific symptoms such as dizziness, headache, nausea and profuse sweating. If not properly treated, heat exhaustion can progress to heatstroke, sometimes over a period of hours or even days.
Heatstroke is marked by an extreme elevation in body temperature — 104 F or higher. It's associated with central nervous system dysfunction that results from heat injury to vital tissues combined with coagulopathies and a systemic inflammatory response. Ultimately, heatstroke can lead to multisystem organ failure and death, explains David W. Claypool, M.D., an emergency physician at Mayo Clinic's campus in Rochester, Minnesota.
"Once the core temperature reaches 104 F, patients have crossed the line from heat exhaustion to heatstroke. They're often combative, confused or delirious, and their reduced mental status can make it difficult to take a full history," he says. "It also can be difficult to distinguish a heat-related illness from intoxication. That's why it's imperative to obtain an accurate core — rectal, esophageal, bladder — temperature.
Treating heat-related illness
Rapid cooling is the main treatment for both heat exhaustion and heatstroke and should start before transport by moving the person into a shady or air-conditioned area, removing restrictive clothing and, if possible, applying cool water to the skin. With these measures and proper hydration, many cases of heat exhaustion resolve fairly quickly.
In the ED, evaporative cooling is usually the most effective method for quickly reducing core temperature in patients with suspected heatstroke and preventing organ damage and death. The goal is to reduce core temperature to 100.4 F within 30 minutes. This can be accomplished in any hospital without the need for sophisticated equipment.
"A spray bottle of tepid water and an electric fan make the best cooling device," Dr. Claypool says. "Patients should be encouraged to drink water or a sports drink to replace fluids. It's a judgment call whether the person is sick enough to require IV fluids.
"Certainly, patients who are hypotensive or tachycardic are at higher risk, as are the very young, the very old, and people who are abusing substances or taking certain medications. In these patients, you would consider IV therapy sooner. You might also want to consider additional testing for electrolytes because heat illness puts tremendous stress on the cardiovascular system. Whether or not cardiac imaging is appropriate is again a judgment call," Dr. Claypool explains.
The need to transfer patients with heatstroke to a higher level of care is clearer. "Because heatstroke can cause multisystem failure, patients need ongoing monitoring and laboratory and neurological assessment in an intensive care unit. Critical access hospitals that don't have the resources to care for these patients should transfer them," Dr. Claypool says.
Even then, the prognosis isn't always good. Some patients experience permanent neurological dysfunction, and myocardial muscle damage can sometimes lead to cardiac arrest.
Who's at risk?
The Chicago heat wave confirmed what many studies have shown — older adults and the poor are the populations most vulnerable to heat-related illness, explains Kimberly (Kim) J. Lombard, injury prevention coordinator at Mayo Clinic's campus in Rochester.
Other groups at high risk include:
- Infants and young children because of their high ratio of surface area to weight and the inability to control hydration
- Athletes exercising strenuously in hot climates
- Outdoor laborers
- People using alcohol or drugs
- Patients with heart or respiratory disease
- People taking drugs that disrupt the body's heat regulatory system or have anticholinergic effects, such as antidepressants, antihistamines, lithium and beta blockers
Both Lombard and Dr. Claypool say most heat-related illness is preventable and that physicians and ED providers can play a vital role in prevention efforts.
"Physicians should discuss the risk of dehydration associated with certain medications, especially when prescribing them for older adults and outdoor workers," Lombard says. "If doctors know that an older patient is socially isolated, they can provide information about available community resources."
Lombard says trauma centers and hospital systems also have an obligation to provide education during unusually hot weather. She suggests that health systems coordinate their efforts with public health services, which are closely connected to the community and already have prevention plans in place. Partnerships between community leaders and health care providers that use the media to inform the public about heat dangers have been shown to improve outcomes among at-risk people.
"It's good to have medical expertise backing up prevention messages because people are more likely to pay attention when the messaging comes from physicians," Lombard says. "Working together, we can have some influence."