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Research at Mass General
Massachusetts General Hospital anesthesiologist Paul Firth, MBChB, has spent the past two decades studying the medical case histories of climbers and other adventurers in order to create a more complete picture of how the body responds to the lack of oxygen at high altitudes.
Billy Joel once sang, “I don’t know why I go to extremes.”
For Massachusetts General Hospital pediatric anesthesiologist Paul Firth, MBChB, the question is not just why people go to extremes, but what physiological changes happen to them when they do.
Firth, an avid mountain climber, explorer and distance runner, has spent the past two decades studying the medical case histories of climbers and other adventurers in order to create a more complete picture of how the body responds to hypoxia, or the lack of oxygen, during periods of intense exertion.
In addition to making him smarter and safer when taking on his own tough physical challenges, this research has given Firth new insights into managing anesthesia delivery for patients with sickle cell disease—an inherited disorder in which oxygenated blood has difficulty traveling through the body.
In a recent interview, Firth said his interest in the science of extremes kicked into gear in 2004, when he was running marathons and planning for a mountaineering expedition to the 29,000-foot peak of Mount Everest.
None of the climbers in his four-person group had ever climbed at heights comparable to Everest before, so Firth researched everything he could about how the body processes oxygen at high altitudes.
Firth's climbing team on the slopes of Mount Everest.
As part of this research, he learned that one of the biggest risks to climbers on Everest is cerebral edema, a condition where fluid passes through the blood brain barrier and causes swelling in the brain.
The swelling restricts the flow of blood, which lowers oxygen levels in the brain and causes a variety of problems, including lethargy, fatigue, the loss of coordination and balance, confusion, and coma.
The rapid onset of these symptoms has led many hikers to make fatal mistakes during climbs on Everest. Due to the unforgiving conditions on the mountain, anything that compromises a climber’s ability to make good decisions and stay on schedule can quickly prove deadly. But Firth’s research revealed something unexpected about the presentation of neurological disability at extreme altitude.
If neurological symptoms were caused primarily by the lack of available oxygen, than one would expect that the most likely time for them to develop would be climbing vigorously right below the summit. For a climber, this would be the time when you are expending a lot of energy with little available oxygen, and arterial oxygen levels are correspondingly lowest.
But after looking back through the death records, Firth found that more climbers developed neurological symptoms on their way back down the mountain, when presumably they would be expending less energy and have more oxygen available. Thus it wasn’t just a lack of arterial oxygen causing the problem, but presumably the progression of cerebral edema arising from the loss of integrity of the blood vessels in the brain.
This knowledge helped Firth make one of the toughest decisions of his mountaineering life back in 2004—to turn back from the summit of Everest when he was just 500 meters (about a third of a mile) from the top.
Firth made the call after an equipment failure cut off part of the team’s supplemental oxygen supply. While all of the factors that contribute to cerebral edema are still not known, taking in supplemental oxygen while you climb has been shown to reduce the risk. “I knew we were [already] climbing too slowly—as a sign something was wrong and that we were not adequately acclimatized—our effort tolerance was down. We were therefore at high risk of developing leaky blood vessels and dying on the way down.”
Firth’s research into cerebral edema on Mount Everest has also informed his research into the anesthetic management of patients with sickle cell disease (SCD).
SCD patients have a genetically inherited disorder in which their red blood cells take an elongated, sickle-like shape (as opposed to the cells’ typically round shape). Patients with SCD experience frequent obstructions in their blood vessels, which can cause episodes of bone pain, difficulty breathing, organ damage and early death.
Traditional anesthetic management of patients with SCD has been founded on the belief that these obstructions and related complications of SCD are exacerbated by low oxygen levels. Thus doctors have traditionally been reluctant to use anesthetics or painkillers that may lower respiration levels, even if that is the proscribed treatment for patients without SCD.
However, Firth’s review of SCD research led him to develop an alternative school of thought—one that suggests the primary cause of SCD complications is due damage to the blood vessels themselves.
This damage impairs the ability of the vessels to deliver oxygenated blood to the body, and makes the vessel walls sticky and more likely to cause blockages. If this approach proves to be correct, than it could be possible to make SCD patients much more comfortable during surgeries, and to give them more options for managing the often-painful side effects of their disease.
More than 10 years after his Everest expedition, Firth still believes he made the right call. In reviewing almost a century’s worth of death reports from Everest, he has found that many climbers encountered similar setbacks on their way up the mountain, but elected to carry on in pursuit of the summit.
They may have reached the top of the world’s tallest mountain, but one climber out of every 30 never made it back down.
“That’s why I turned around and why I think we all survived, because I’d researched what the problems were going to be.”
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