Millions of Americans have been languishing for weeks in the oppressive heat and humidity of a merciless summer. Deadly heat has already taken the lives of hundreds in the Pacific Northwest alone, with numbers likely to grow as the full impact of heat-related deaths eventually comes to light.
In the final week of July, the National Weather Service issued excessive heat warnings for 17 states, stretching from the West Coast, across the Midwest, down south into Louisiana and Georgia. Temperatures 10° to 15° F above average threaten the lives and livelihoods of people all across the country.
After a scorching heat wave in late June, residents of the Pacific Northwest are once again likely to see triple-digit temperatures in the coming days. With the heat, hospitals may face another surge of people with heat-related illnesses.
Erika Moseson, MD, a lung and intensive care specialist, witnessed firsthand the life-threatening impacts of soaring temperatures. She happened to be running her 10-bed intensive care unit in a suburban hospital in Gresham, Ore., about 15 miles east of Portland, the weekend of June 26. Within 12 hours, almost half her ICU beds were filled with people found unconscious on the street, in the bushes, or in their own beds, all because their body’s defenses had become overwhelmed by heat.
“It was unidentified person after unidentified person, coming in, same story, temperatures through the roof, comatose,” Dr. Moseson recalled. Young people in their 20s with muscle breakdown markers through the roof, a sign of rhabdomyolysis; people with no other medical problems that would have put them in a high-risk category.
As a lifelong Oregonian, she’d never seen anything like this before. “We’re all trained for it. I know what happens to you if you have heatstroke, I know how to treat it,” she trailed off, still finding it hard to believe. Still reeling from the number of cases in just a few hours. Still shocked that this happened on what’s supposed to be the cooler, rainforest side of Oregon.
Among those she treated and resuscitated, the memory of a patient that she lost continues to gnaw at her.
“I’ve gone back to it day after day since it happened,” she reflected.
Adults, in their 50s, living at home with their children. Just 1 hour prior, they’d all said goodnight. Then 1 hour later, when a child came to check in, both parents were unconscious.
Dr. Moseson shared how her team tried everything in their power for 18 hours to save the parent that was brought to her ICU. But like hundreds of others who went through the heat wave that weekend, her patient didn’t survive.
It was too late. From Dr. Moseson’s experience, it’s what happens “if you’re cooking a human.”
How heat kills
Regardless of where we live on the planet, humans maintain a consistent internal temperature around 98° F for our systems to function properly.
Our bodies have an entire temperature-regulating system to balance heat gain with heat loss so we don’t stray too far from our ideal range. The hypothalamus functions as the thermostat, communicating with heat sensors in our skin, muscles, and spinal cord. Based on signals about our core body temperature, our nervous system makes many decisions for us – opening up blood vessels in the peripheral parts of our body, pushing more blood toward the skin, and activating sweat glands to produce more sweat.
Sweat is one of the most powerful tools we have to maintain a safe internal temperature. Of course, there are some things under our control, such as removing clothing, drinking more water, and finding shade (or preferably air conditioning). But beyond that, it’s our ability to sweat that keeps us cool. When sweat evaporates into the air, heat from our skin goes with it, cooling us off.
Over time, our sweat response can work better as we get used to warmer environments, a process that’s known as acclimatization. Over the period of a few days to weeks, the sweat glands of acclimated people can start making sweat at lower temperatures, produce more sweat, and absorb more salt back into our system, all to make us more efficient “sweaters.”
While someone who’s not used to the heat may only produce 1 liter of sweat per hour, people who have become acclimated can produce 2-3 liters every hour, allowing evaporation to eliminate more than two times the amount of heat.
Because the process of acclimatization can take some time, typically it’s the first throes of summer, or heat waves in places where people don’t typically see high temperatures, that are the most deadly. And of course, the right infrastructure, like access to air conditioning, also plays a large role in limiting heat-related death and hospitalization.
A 2019 study showed that heat-related hospitalizations peak at different temperatures in different places. For example, hospitalizations typically peak in Texas when the temperature hits 105° F. But they might be highest in the Pacific Northwest at just 81° F.
Even with acclimatization, there are limits to how much our bodies can adapt to heat. When the humidity goes up past 75%, there’s already so much moisture in the air that heat loss through evaporation no longer occurs.
It’s this connection between heat and humidity that can be deadly. This is why the heat index (a measure that takes into account temperature and relative humidity) and wet bulb globe temperature (a measure commonly used by the military and competitive athletes that takes into account temperature, humidity, wind speed, sun angle, and cloud cover) are both better at showing how dangerous the heat may be for our health, compared to temperature alone.
Kristie L. Ebi, PhD, a professor in the Center for Health and the Global Environment at the University of Washington, Seattle, has been studying the effects of heat and other climate-sensitive conditions on health for over 20 years. She stresses that it’s not just the recorded temperatures, but the prolonged exposure that kills.
If you never get a chance to bring down that core body temperature, if your internal temperatures stay above the range where your cells and your organs can work well for a long time, that’s when you can have the most dangerous effects of heat.
“It depends then on your age, your fitness, your individual physiology, underlying medical conditions, to how quickly that could affect the functioning of those organs. There’s lots of variability in there,” Dr. Ebi said.
Our hearts take on the brunt of the early response, working harder to pump blood toward the skin. Water and salt loss through our skin can start to cause electrolyte changes that can cause heat cramps and heat exhaustion. We feel tired, nauseated, dizzy. With enough water loss, we may become dehydrated, limiting the blood flow to our brains, causing us to pass out.
These early signs are like a car’s check engine light – systems are already being damaged, but resting, refueling, and, most importantly, turning off the heat are critical steps to prevent fatal injury.
If hazardous heat exposure continues and our internal temperatures continue to rise, nerves stop talking to each other, the proteins in our body unfold and lose their shape, and the cells of our organs disintegrate. This in turn sets off a fire alarm in our blood vessels, where a variety of chemical messengers, including “heat-shock proteins,” are released. The release of these inflammatory proteins, coupled with the loss of blood flow, eventually leads to the death of cells throughout the body, from the brain, to the heart, the muscles, and the kidneys.
This process is referred to as heatstroke. In essence, we melt from the inside.
At a certain point, this cascade can’t be reversed. Just like when you cool a melting block of ice, the parts that have melted will not go back to their original shape. It’s a similar process in our bodies, so delays in cooling and treatment can lead to death rates as high as 80%.
On the outside, we see people who look confused and disoriented, with hot skin and rapid breathing, and they may eventually become unconscious. Core body temperatures over 105° F clinch the diagnosis, but at the first sign of feeling unwell, cooling should be started.
There is no fancier or more effective treatment than that: Cool right away. In emergency rooms in Washington State, doctors used body bags filled with ice and water to cool victims of the heat wave in late June.
“It was all from heat ... that’s the thing, you feel so idiotic ... you’re like, ‘I’ve given you ice’ ... you bring their temperature down. But it’s already set off this cascade that you can’t stop,” Dr. Moseson said.
By the time Dr. Moseson’s patient made it to her, cooling with ice was just the beginning of the attempts to resuscitate and revive. The patient was already showing evidence of a process causing widespread bleeding and clotting, known as disseminated intravascular coagulation, along with damage to the heart and failing kidneys. Over 18 hours, her team cooled the patient, flooded the blood vessels with fluids and blood products, attempted to start dialysis, and inserted a breathing tube – all of the technology that is used to save people from serious cardiovascular collapse from other conditions. But nothing could reverse the melting that had already occurred.
Deaths from heat are 100% preventable. Until they’re not.