On the third day of the “heat dome” that enveloped the Pacific Northwest in the summer of 2021, Steven Mitchell, MD, FACEP, medical director of emergency services at the University of Washington (UW) Harborview Medical Center in Seattle, realized that he was witnessing a true disaster unfolding.
Three days of temperatures above 104 degrees, in a city where many residents had no air conditioning, was sending unprecedented numbers of patients to Harborview and its affiliated hospitals. The county’s emergency medical services responded to roughly 1,100 calls that day — more than twice the average and the busiest day on record. So many patients were coming into UW’s Valley Medical Center with severe, life-threatening heat stroke that the hospital was in danger of running out of ventilators.
“The people who were working that day at Valley Medical Center saw a career’s worth of heat stroke in a matter of a few hours,” says Mitchell, who also serves as medical director of the Washington Medical Coordination Center, which was established during the COVID-19 pandemic to assist in coordinating the state’s disaster preparedness activities. “It became overwhelming quickly for hospital systems in particular that had already been under a lot of stress and strain.”
The disaster that hit Seattle during that summer is likely to play out many times over in the coming years, as climate change accelerates the frequency, duration, and intensity of extreme heat events. The U.S. Environmental Protection Agency estimated there were three times as many heat waves annually during the last decade than there were during the 1960s (six per year across 50 major metropolitan areas, compared with two per year a half century ago). Those heat waves also are longer (four days compared to three) and hotter on average, creating havoc for humans and health care systems.
Indeed, in the United States, approximately 67,500 people visit the emergency department (ED), 9,200 people are hospitalized, and 700 people die each year due to heat, according to the Centers for Disease Control and Prevention’s Heat and Health Tracker. Globally, heat-related deaths increased by 68% between 2000-2004 and 2017-2021. Older people, infants, pregnant women, people who work outdoors, and those without social supports were most vulnerable, according to the 2022 Report of the Lancet Countdown on Health and Climate Change.
Heat and the human body
Humans actually are quite adaptable and can tolerate very high levels of heat and humidity — but only for short periods of time, says W. Larry Kenney, PhD, FACSM, a professor of physiology and kinesiology at Penn State University and an expert on the impacts of heat on the human body.
Kenney first began studying those impacts during graduate school at Penn State, when he did a series of research projects at the Three Mile Island nuclear power station, which had a catastrophic meltdown in 1979. Workers who were tasked with fixing the crippled reactor would dress in two — and sometimes three — layers of plastic clothing, with rubber gloves that were taped shut and respirators and hoods to protect them from radiation. “Essentially it was like trying to go to work in a Ziploc bag, where the temperatures were sometimes as high as 165 degrees Fahrenheit,” Kenney says. “These workers could go in and work for about 20 minutes and then were exhausted and overheated and had to come out.” His team monitored the workers, conducted medical screenings, and even developed a personal heat stress monitor that would tell them when it was time to get out.
That initial research sparked Kenney’s interest in the health-related outcomes of heat on other populations — work that has become even more relevant as climate change accelerates both the average surface temperature of the earth and the incidence of heat waves. His lab most recently won a multi-year grant from the National Institutes of Health to establish the upper limits of temperature and humidity beyond which humans are unable to cool themselves, a point the researchers call “uncompensable.” Already, heat waves across the globe have exposed people to these limits, with disastrous consequences, particularly in developing countries where resources are limited.
At its most basic, when humans are exposed to heat, either through the environment or during exercise, their core body temperature begins to rise, Kenney explains. The body compensates in two ways — by increasing blood flow to the skin and by producing eccrine sweat, which evaporates into the air, thus transferring that heat back into the environment.
Up to a certain point, the body is able to maintain its thermoregulatory capacity. But problems arise during a few scenarios.
Excessively humid conditions: In warm, humid conditions, sweat may not evaporate as well, which could cause the body to retain some of that excess heat. Any rise in core body temperature can have deleterious effects, from heat exhaustion to heat stroke.
Excessive sweating: Periods of prolonged sweating can result in dehydration and a loss of blood volume. Since greater blood volume is needed to pump excess heat to the skin and out of the body, a loss in blood volume can result in higher core temperatures.
Preexisting cardiovascular disease: All the mechanisms involved in cooling the body put a strain on the heart, as the left ventricle has to work extra hard to pump blood to the skin. The elderly and those with heart disease may find themselves quickly overwhelmed; in fact, most of those who die during heat waves actually succumb to cardiovascular disease, Kenney says. Between 70% and 95% of the people who die during heat waves are over the age of 65.
Prompt treatment is critical
When the first patients with acute heat stroke began arriving at the Harborview ED in the summer of 2021, Mitchell and his team immediately ordered extra body bags and ice to be on hand. Patients suffering from heat stroke were placed onto gurneys in body bags filled with an ice-water slurry, which allowed the medical team to begin administering lifesaving treatment while simultaneously cooling the patient as rapidly as possible.
It was a treatment first outlined the previous year in the Journal of the American College of Emergency Physicians, in a case study co-authored by Grant Lipman, MD, who at the time was an emergency medicine physician at Stanford Medicine and director of its Wilderness Medicine Fellowship program. Lipman and his team had treated an elderly patient who was found unconscious in a parking lot during the middle of a heat wave. Her core temperature had reached 104 degrees Fahrenheit, and she was confused — both signs of acute heat stroke.
Upon arrival at the hospital, Lipman and his team decided to try the body bag filled with ice water experiment. After 10 minutes of immersion in the icy water, the patient’s body temperature was down to 101.1 degrees Fahrenheit and her mental status was normal. She was discharged later that day with no residual issues.
“From all the research out there, we know that ice cold water immersion is the quickest way to just suck heat out of the body, since water transfers heat 25 times faster than air,” Lipman says. “But it’s just not very realistic” in an ED, where medical teams also need to be able to access the patient’s chest to monitor vital signs. “We were talking about using a body bag, but no one I knew had really done it. And literally that next day … this patient showed up.”
Lipman and his team published their findings, which were read by the ED team in Seattle. “The whole point of publication is to get knowledge to people who need it,” Lipman says. “When I wrote this, I was thinking, ‘In the case of an extreme heat emergency, this is a quick, easy, scalable solution.’ Then I hear these folks in Seattle are using it. … It’s really exciting to see that being implemented and hopefully saving some lives.”
Cooling the body rapidly is the key to saving not just lives, but organ function. Lipman describes the pathophysiology of heat stroke as being similar to that of sepsis. Once the core temperature rises to a dangerous level, there’s a breakdown of protective heat-shock proteins, the gut starts leaking bacteria and other toxins into the bloodstream, the inflammatory response kicks in, and organs start deteriorating. “If you think of the time-temperature curve, the longer you’re injuring cells and structures and systems, the worse you’re going to do,” Lipman says. Cold-water immersion can cool down the body in less than 10 minutes, whereas evaporative cooling can take up to 45 minutes.
Preventing heat illness
As one of the first physicians to be certified in wilderness medicine, Lipman was instrumental in developing the Wilderness Medicine Society Practice Guidelines for the Prevention and Treatment of Heat Illness — a how-to guide for treating heat illness outside the hospital.
He has also developed an app called GOES Health: Global Outdoor Emergency Support, which offers on-demand wilderness medical support 24/7, to help people prepare for outdoor activities — and make emergency decisions when off the grid.
Perhaps one of the best prevention methods for successfully weathering an extreme heat event is acclimatization, or a slow adjustment to the heat. An average person needs to be exposed to the heat for 1 to 2 hours over nine to 14 days to become fully acclimatized, Kenney says, with most of the heat acclimatization occurring in the first four or five days. “That’s because the key thing that allows humans to acclimate to the heat is an expansion of blood volume,” he says.
Seattle normally has a temperate climate, which meant that few were acclimated to the heat when the heat dome hit in the summer of 2021. Many also didn’t have the ability to escape the heat. “Almost to a person, those who died were living in housing without air conditioning,” Mitchell says.
“Air conditioning is the great savior and equalizer,” Kenney acknowledges. “If you’re 90 years old, but you have access to air conditioning, you’re not going to be harmed by the heat. But somebody who’s homeless, for example, and outside in those conditions, or an individual [who] because of socioeconomic factors doesn’t have access to air conditioning, is … going to be affected.”
That’s why hospitals in Seattle and the surrounding environs have implemented a new disaster preparedness plan for heat events — in addition to existing plans for events such as earthquakes, fires, and tornadoes. “Whenever high temperatures are forecasted, all of the hospitals in the region meet to review best practices,” Mitchell says. “And that includes, ‘Do you have body bags? Do you have ice available? Do you have fans that can blow cool air in addition to cooling catheters?’
“We have to be better prepared,” he adds. “Our infrastructure, our communities, our education in how we care for vulnerable populations, has got to be better because the impacts are going to increase as the frequency of these events increases.”