When a patient’s blood oxygen levels drop below 90 percent in the emergency room in the United States, many doctors panic.
The body needs oxygen in order to transfer the energy stored in food into usable energy. If the body is deprived of oxygen for too long, organs begin to shut down.
However, on top of Mount Everest— the tallest mountain in the world at 29,029 feet—many people reach oxygen levels of 60 percent and yet manage to function reasonably well.
An international medical research team known as Xtreme Everest studies how people respond to low-oxygen levels at high altitudes in order to better understand critical illness. The organization, which was started by scientists in the United Kingdom, has hosted more than five expeditions over the past 15 years in which teams of investigators, scientists, volunteer trekkers, and Sherpas were monitored during ascent and descent of Mount Everest.
Three Duke researchers participated in the 2013 and 2017 expeditions— Richard Moon, MD, a professor of anesthesiology and medicine, and medical director of Duke’s Center for Hyberbaric Medicine and Environmental Physiology; Chris Young, MD, a critical care specialist and professor of anesthesiology; and Eugene Moretti, MD, a critical care specialist and professor of anesthesiology.
At a symposium held June 14 at Duke University, hosted by Duke Anesthesiology, scientists from Duke, the University of Southampton, University College London (UCL), and University of Cambridge, met to discuss their most recent findings. Listeners from all over the world—including Australia, Portugal, Croatia and Argentina— tuned in live.
“We wanted to have the opportunity to present an up-todate summary of what we have learned so far, including data from our Sherpa volunteers,” said Kay Mitchell, senior research manager in the critical care research area at the NIHR Southampton Biomedical Research Center and co-founder of Xtreme Everest.
Last year, in 2017, the group published a paper in the journal Proceedings of the National Academy of Sciences reporting their findings. Their research showed that there are metabolic adaptations in the Sherpas who guide people up Mount Everest that allow their tissues to use oxygen more efficiently. This adaptation, which is reinforced by genetic differences, allows Sherpas to conserve muscle energy at high altitudes and possibly contributes to their superior climbing abilities at extreme altitudes.
The ways in which individuals adjust differently to low-oxygen environments is a key point of study for Xtreme Everest. Over the past several years, the researchers have been able to identify what the body can withstand when it acclimates, such as a disruption to the cardiovascular system’s microcirculation, an alteration in mitochondrial function and, in some cases, high-altitude cerebral edema— the potential fatal condition in which the brain swells and fills with fluid. However, they have not yet solved the mystery as to why some people acclimate differently than others.
In many cases, those considered most physically fit prior to the trip are not the ones who make it up the mountain and back most quickly or easily.
“It’s very counterintuitive,” said Michael Grocott, MD, professor of anaesthesia and critical care medicine at the University of Southampton and co-founder of Xtreme Everest. “We have this delightful phenomenon where by those who are the fittest lose the largest amount of oxygen, not just in absolute terms, but proportionally. This completely fits with the anecdotes you get from guides at Everest who take people up every year.”
Understanding how an individual might uniquely acclimate to lower oxygen levels is important not only on mountain tops but also in the hospital room.
Patients suffering from any lung-related condition, such as an asthma attack, pneumonia, pulmonary edema, lung injury, or some drug overdoses in which hypoventilation occurs, may receive oxygen treatment while in the hospital. However, there is debate in the scientific literature about whether critical care doctors are overusing oxygen, or rather, giving higher concentrations of oxygen to patients than is needed.
“Administering oxygen can be toxic to the lung,” said Richard Moon, MD, a professor of anesthesiology and medicine, and medical director of Duke’s Center for Hyberbaric Medicine and Environmental Physiology and member of Xtreme Everest. “An alternative approach to that would be to give a drug, if it existed, to reacclimatize the person to low-oxygen levels. If there were such a medicine, it would be extremely useful and maybe life-saving to a lot of people.”
Moon uses the word ‘reacclimatize’ because everyone has been exposed to a low-oxygen environment as a fetus in the mother’s womb. Over time, our bodies acclimated to the oxygen-rich environment outside of the fetus. A person can re-acclimate to a low-oxygen environment if given enough time. This is why Mount Everest climbers must carefully plan out their journeys over days to allow the body time to acclimate.
Moon, who has studied the body’s response to altitude since 1980, first participated in an Xtreme Everest study in 2013, along with Young and Moretti. They were also joined by Anna Grodecki, a former Duke fellow, Nelson Diamond, a former Duke medical student, and Richard Moon’s son, Peter Moon.
Moon will never forget the moment the group landed in Lukla, Nepal, which is historically home to the world’s most dangerous airport; at an altitude of 9,383 feet, it is precariously situated on a cliff in the Himalayan mountains with a short runway that leaves little room for error. High winds, cloud cover, rain and unpredictable visibility complicates landing.
Lukla serves as an entryway to Everest, and this is where most people begin the excruciating 40-mile climb to base camp, which is located at 17,500 feet. From there, trekkers ascend more than 10,000 feet to the summit of Everest. Since Sir Edmund Hillary’s initial summit in 1953, only about 4,000 people have summited Mount Everest. Each year, approximately 800 people attempt the climb, and a handful of people, on average, die each year as a result. In addition to the physical fitness required, trekkers face the dangers of avalanche, ice collapse, frost bite, exposure, and the mountain’s “death zone”—the area above 26,000 feet where the oxygen level is not sufficient to sustain human life. Trekkers who reach that altitude without supplemental oxygen have a limited amount of time before major organs begin to fail from oxygen deprivation.
Moon was there to participate as a volunteer for Xtreme Everest, which was sending groups of 14 people up the mountain in two-day intervals, and monitoring their heart rate, blood pressure, and weight throughout the course of the trip. But he was also there to collect his own data from 10 people wearing pulse oximeters in order to determine the level of oxygen saturation in their blood.
The numbers that Moon began to see on the pulse oximeters as the group ascended from Lukla to base camp to the village of Namche and beyond were alarming.
“It was quite surprising to me, and I think to the other physicians, because in the United States we all start getting nervous when a patient’s oxygen saturation drops below 90 percent, but when we landed in Lukla and our oxygen saturation was in the mid-80s, everyone felt perfectly fine,” said Moon. “And then, when we started walking, it dropped further, and over the next few days we realized we were in the 70s and, then, the 60s at night. The human body is much more resilient than we think, or at least the healthy human body. Obviously, when people have disease, it’s different.”
Moon said the data, which is still being analyzed, along with data collected from the follow-up trip in 2017, will provide some degree of reassurance to doctors that low oxygen levels are not intrinsically harmful to most people, even very low oxygen levels.
The 2013 and 2017 expeditions were extremely successful with just a few hiccups. One member of Moon’s group during the 2013 expedition had to be helicoptered back to Lukla when the group noticed she was having trouble putting sugar in her tea. A neurologist back home confirmed high altitude cerebral edema and the group member received care for weeks afterwards. Likewise, during the 2017 expedition, two physicians in his group had to leave due to high altitude cerebral edema. Luckily, everyone recovered once back at lower altitude.
“The view of so many 8,000 meter plus peaks was both unique and magnificent,” said Moretti. “It was a formidable challenge on the part of the UCL and Duke teams to manage the logistics involved in the research endeavor. However, this provided us with an extraordinary opportunity to conduct high quality research in multiple areas of physiology. Doing this in one of the most extreme environments in the world, made this a truly remarkable experience.”
The Duke group continues to analyze data from the 2013 and 2017 expeditions, and has their sights set on 2020 for another potential data-gathering adventure in the mountains.
First published in BluePrint