17 Nov, 09 | by BMJ Group
Dan Martin undresses in 20-knot winds beneath the Everest summit to prepare for a femoral artery blood sample and muscle biopsy while a team of sherpas look on, entertained by what they see. The critical care anaesthetist and his three colleagues ended up on the top of the world’s highest peak two years ago as part of their research project to quantify the limit of human tolerance for hypoxia.
Describing the experiment so far at a Wellcome Collection event in London last week, Martin said he and his three colleagues recorded an average blood oxygen level of 54% (3.28 kilopascals or kPa). His was the lowest, at 34% (2.55 kPa). Patients with a level below 8 kPa are considered critically ill.
The samples were put into non-permeable glass syringes, which are very difficult to handle, and transferred to ice-filled vacuum containers, which the sherpas quickly deposited at a lab 200m below.
The research team’s bid to discover “how low can you go” via Everest was seen as preferable to putting a large number patients on a round of low oxygen in a hypobaric setting. Martin said: “Hypobaric is unpleasant. It’s a windowless steel tube. We were at altitude for 72 days I would not have liked to sit in a tube for 72 days.”
Neither was it practicable. A large chamber study would have risked some people suffering the bends, he added. Even so, the team spent two years using this environment to measure their equipment’s efficiency in preparation for the trip.
They encountered scepticism along the way. The team was thought to be “a bit mad,” so they could not seek funding through the normal routes. Eventually the gas/oxygen company BOC provided finance, even through, ironically, their research was about the lack of it.
Martin’s “madness” extends to his physiological reaction to hypoxia. It’s very rare to gain weight at altitude. Most people shed kilograms, mainly due to a dramatic loss of muscle density (often 30%), despite a daily diet of up to 6000 calories, including eating neat butter to keep the weight on.
But Martin, as well as recording a 34% arterial blood sample hypoxia reading (something most doctors would never see in a hospital patient), gained 3kg.
The team also hauled exercise bikes up the mountain, to test metabolic efficiency, in a similar way to Olympic athletes training at high altitudes to make them more efficient when the perform closer to sea level.
The research team’s goal, given that oxygen is highly toxic, is to see if a hypoxic patient’s physiology can somehow be altered to enable them to survive better in a critical care setting.
Elsewhere in the animal kingdom, for example, mammals “switch their bodies into different modes” to handle low-oxygen environments.
So what’s the next step? For Martin, it’s moving beyond an observational study to an intervention or pharmacological one.
But might sherpas, who regularly function at high altitudes, hold the key?
Martin told the meeting: “From the few experiments that have been done on sherpas they don’t carry any more oxygen than we do. If sherpas become ill in ITU we expect them to do better.
Why was their arterial blood and muscule tissue not sampled on the summit? “They were very keen for us to take their blood but we couldn’t for ethical reasons,” explained Dan.
David Payne is editor, bmj.com and doc2doc.bmj.com
Everest also featured in the Christmas 2008 BMJ: