Heat stroke occurs when your core body temperature rises above 104°F (40°C) while you also experience profound changes in brain function -- "alterations in consciousness or mental status," said Dr. Corey Slovis, a professor and chair of Emergency Medicine at Vanderbilt University Medical Center.
These two circumstances are also "usually associated with profound cardiovascular side effects of low blood pressure and elevated heart rate," said Slovis.
Under these conditions of heat stroke, "you are at risk for permanent brain, heart and kidney damage and you are at risk for death since heat stroke is potentially fatal," he said.
Heat stroke may also be referred to as hyperthermia and heat illness.
What happens when the human body endures extreme heat?
When temperatures rise inside the body, your cells become deranged and chaotic, said Craig Crandall, a professor of Internal Medicine at University of Texas Southwestern Medical Center. Crandall is also a director of the thermal and vascular physiology laboratory at Texas Health Presbyterian Hospital Dallas. The resulting cascade of events, then, "greatly affect the central nervous system, the brain, and ultimately the organs."
"As far as the brain is concerned, it starts to shut down," said Crandall. The brain swells, individual brain cells stop working and since it is their job to communicate throughout the system, "the organs stop receiving the appropriate information from the brain."
In addition, inflammation can begin affecting brain function and nerve function, said Crandall. Cytotoxins -- cytokines is the formal term -- are released throughout the body due to heat stress and these are detrimental to organ function.
"One of the things that happens is your intestines, your gut, the permeability increases because of these cytokines released," said Crandall. "Some of the substances that are normally kept within the gut get suddenly released."
This occurs because the blood vessels are massively dilated and pressure is reduced. "A septic shock would be an analogous scenario. That can be a big problem," Crandall said.
"When it gets too hot, the blood can clot or start to and that obviously will affect circulation and transportation of oxygen and nutrients," said Crandall. The oxygen and nutrients are necessary food for the body and its organs, including the brain.
"So the person would pass out and likely be in a coma and can convulse and if it continues will lead to organ failure and ultimately death, which happened, tragically, in some of these individuals who were in that trailer," said Crandall. "It's just a bad scenario all around."
What are the warning signs and symptoms of heat illness?
The warning signs of impending heat illness include high body temperature, according to the Centers for Disease Control and Prevention.
Hot, red, dry, or damp skin and a fast strong pulse are also warning signs, the CDC warns.
Symptoms might include headache, feeling dizzy, nausea, feeling confused and losing consciousness (passing out).
"You're really hyperventilating a lot and you're blowing off a lot of CO2 which can cause problems," said Crandall. "Of course, you're extremely dehydrated because you're releasing all this sweat and you're not taking in any fluid and that will exacerbate all these different [symptoms]."
Each case, though, varies. Some people may reach the danger zone, experience only mild symptoms, such as a headache, and then that disappears once they rest and rehydrate. In other cases, though, a cascade of events may occur where the organs begin to shut down and the body is no longer able to regulate blood pressure and the blood does not coagulate. Death could follow.
Are there different types of heat stroke?
There are two types of heat stroke. "One is called exertional heat stroke," said Slovis. This commonly affects athletes, such as football players or road racers in a tight pack, who exercise strenuously and their bodies can't dissipate the heat fast enough.
"More commonly, and what was seen in this case is the classic heat stroke -- passive heat stroke -- where people become increasingly dehydrated," said Slovis.
"We normally get rid of excess body heat by sweating and we evaporate and we lose heat via evaporation," said Slovis. With dehydration, though, we "lose the ability to sweat, the body loses the ability to get rid of heat, and so body temperature rapidly rises," he said.
The two things that increase the likelihood of heat related illness is inability to sweat and increasing humidity and heat.
"If you're in a hot container, as body temp rises, as humidity rises inside there, you cannot dissipate heat," said Slovis.
What is the treatment for heat stroke?
"When we treat people for heat stroke, what I like to say is the two things we want to do is keep the person wet, and keep the person winded," said Slovis, adding that you want "to rapidly cool the patient, to rapidly rehydrate the patient, and to get the body temperature to as close to normal as quickly as possible."
"People have used ice baths, they've used spraying people with tepid water and having fans blow on them," said Slovis. A combination of two is used in emergency rooms. "Ice packs are put under the groin, under the armpits, under the neck and the person is sprayed with water as fans run air current across them to maximize evaporation," he said.
In general, cooling the patient rapidly is most commonly used without any medication.
What is the likelihood of a complete recovery following heat illness?
Athletes who get heat stroke almost invariably do well, said Slovis. And it is "potentially totally curable" in healthier patients who receive treatment immediately. "Although many patients with heat stroke recover completely, they're at increased risk for heat stroke in the ensuing days, weeks and months," said Slovis.
Still, no matter who you are, once your temperature rises above 104 and profound changes in brain function occur, "you are at risk for permanent brain, heart and kidney damage and you are at risk for death since heat stroke is potentially fatal," said Slovis. "The things we fear the most are renal damage, cardiac events, and something called rhabdomyolysis -- or muscle break down that may cause permanent kidney damage. Anything is possible due to heat stroke."
The damage begins immediately, yet the results depend on both time and the individual. Essentially, the longer the body is at high temperatures, the greater the risk to each organ system.
"The sooner you're cooled, the healthier you are, the better you will do in a relatively unpredictable way," said Slovis. "I want to stress to you it is variable and each individual is different as far as how he or she is going to do. There's some point in each individual where the heat, the inflammation, the multi-organ system failure reaches a point where the patient can no longer be saved and that's different for each individual."
Who is vulnerable?
The two groups most vulnerable are the very young and the very old, said Slovis, who noted that neither group can "control heat regulation as well as a mature individual."
"And it's also based on the patient's underlying health, what medications they're on, whether they have heart, kidney, or liver disease, and just their underlying health and hydration prior to the heat stress," said Slovis.
What can be done to protect against heat shock?
Heat-shock proteins also factor into vulnerability, explained Crandall. Heat-shock proteins are stress proteins contained in each of our cells that protect the function of our cells, while also aiding immune response.
"The more that we're adjusted to heat, the more of these heat shock proteins we have," said Crandall. So people who work outside or exercise a lot are usually more acclimated to the heat and therefore are less likely to succumb to heat illness.
"There's no question exercise will increase core temperature and prove to be beneficial and adaptive responses will occur," said Crandall.
Along with acclimation, a person can wear loose-fitting clothing while in the sun
, drink plenty of water, take it easy during the hottest part of the day, and never remain in a enclosed space like a car, according to the Mayo Clinic.