Just when it seems the hottest days of summer have passed, high heat-index days return. In July, McDonough District Hospital’s emergency department treated nearly 50 patients for heat-related illness this summer. There were more cases during this month’s stretch of excessive heat and humidity.
Community News Brief spoke with Steven Parkes, M.D., medical director of the hospital’s emergency department, about recognizing, preventing and responding to heat-related illness.
What are the symptoms of heat exhaustion?
People often begin by simply feeling unusually tired. If they continue to push through while becoming dehydrated, symptoms progress to headache, heart palpitations, nausea, vomiting, diarrhea and eventually collapse. These signs reflect progressive fluid and electrolyte loss.
What is the difference between heat exhaustion and heat stroke?
Heat stroke is defined by a change in mental status – confusion, delirium, inability to speak clearly or failure to recognize familiar people. It is a medical emergency. Headache and vomiting can occur in both conditions, but once mental status is altered, the situation has become critical. Severe cases commonly produce significant electrolyte disturbances, particularly low potassium, magnesium and sodium.
Why is the most severe form of heat illness called a “stroke?” The name reflects the profound effect on brain function. In a typical ischemic stroke, a blood clot kills brain tissue. In heat stroke the brain is not dying from lack of blood flow, but its normal function is severely disrupted by extreme body temperature.
Are there long-term complications from heat stroke?
Most people who receive prompt cooling and supportive care recover fully, sometimes after a few days of hospitalization. However, medical literature documents that severe heat stroke can leave lasting effects in some patients, including neurological changes (particularly cerebellar dysfunction), increased long-term cardiovascular risk, and, less commonly, kidney or other organ issues. It is not something to take lightly.
Does extreme heat and humidity affect older and younger people differently?
Tolerance declines with age. Older adults generally have reduced ability to regulate temperature, diminished thirst sensation and less physiologic reserve. Younger people often rebound more quickly at the cellular level, yet they are also more likely to be outdoors performing physical work or exercise and ignore early warning signs. Hydration status, energy reserves and the intensity of activity matter more than age alone.
Does the spiral of symptoms often occur before people realize how serious it has become?
Yes, especially among younger individuals. They may feel mildly tired, remain in “work mode” and keep pushing. By the time they recognize the problem, they can already be near collapse. Early signals should never be ignored; they only grow louder.
What is the first thing to do if heat exhaustion is suspected?
Move the person out of the heat immediately – into air-conditioned space, if possible. Shade alone is not enough when the outdoor temperature is still in the mid-90s with high humidity.
What about heat stroke?
Call 911 or arrange immediate transport to an emergency department. Do not drive yourself.
Is water or an electrolyte sports drink better for dehydration?
Water is the best starting fluid. When someone has been sweating heavily, some electrolyte replacement is useful. Roughly one-quarter to one-half of fluid intake can come from an electrolyte beverage.
Avoid relying on coffee, energy drinks or sodas. These are sometimes called “anti-waters” because they add physiologic stress when the body is already dehydrated. Caffeine has a mild diuretic effect (especially at rest) and can mask fatigue, prompting people to push further when they should be recovering. That combination raises the risk of progressing to heat stroke.
How much should a person drink?
A practical baseline is approximately one-half ounce of fluid per pound of body weight per day. In hot weather or during physical exertion, needs can easily double or triple. Thirst is an imperfect guide; pale urine is a more reliable marker of adequate hydration.
Steven Parkes, M.D.
Are heart and lung problems made worse by excessive heat and humidity?
Yes. Any chronic medical condition is stressed by heat.
Patients with COPD, emphysema or prior heart disease must work harder to maintain circulation and oxygenation.
Being outdoors in high heat and humidity is physiologically similar to a stress test, except the person is not monitored.
Simply sitting in extreme heat can elevate heart rate as much as moderate exercise would in cooler conditions.
Is there a cumulative effect of successive hot days?
Definitely. The third or fourth consecutive high heat-index day is typically more dangerous. The body has already accumulated stress and has less residual resilience. A single abrupt hot day after a stretch of milder weather usually produces fewer cases than a multi-day heat wave.
Why is a 116-degree heat index caused by humidity more dangerous than 116 degrees of dry heat?
In dry heat the body can still cool itself effectively through evaporation of sweat. In the high-humidity conditions typical of the Midwest, sweat does not evaporate well; cooling fails. An 88-degree day with very high humidity can therefore be more physiologically stressful than a hotter but drier day. Local relative humidity commonly ranges from 70 to 90 percent.
Does staying inside an air-conditioned building fully prevent heat-related illness?
Air conditioning is protective and far preferable to outdoor exposure. However, continuous air conditioning can dry the air and increase insensible fluid losses, so people still need to maintain intentional hydration even indoors.
