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Previous Volume 360:140-149 January 8, 2009 Number 2 Next

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ABSTRACT

Background The level of environmental hypobaric hypoxia that affects climbers at the summit of Mount Everest (8848 m [29,029 ft]) is close to the limit of tolerance by humans. We performed direct field measurements of arterial blood gases in climbers breathing ambient air on Mount Everest.

Methods We obtained samples of arterial blood from 10 climbers during their ascent to and descent from the summit of Mount Everest. The partial pressures of arterial oxygen (PaO₂) and carbon dioxide (PaCO₂), pH, and hemoglobin and lactate concentrations were measured. The arterial oxygen saturation (SaO₂), bicarbonate concentration, base excess, and alveolar–arterial oxygen difference were calculated.

Results PaO₂ fell with increasing altitude, whereas SaO₂ was relatively stable. The hemoglobin concentration increased such that the oxygen content of arterial blood was maintained at or above sea-level values until the climbers reached an elevation of 7100 m (23,294 ft). In four samples taken at 8400 m (27,559 ft) — at which altitude the barometric pressure was 272 mm Hg (36.3 kPa) — the mean PaO₂ in subjects breathing ambient air was 24.6 mm Hg (3.28 kPa), with a range of 19.1 to 29.5 mm Hg (2.55 to 3.93 kPa). The mean PaCO₂ was 13.3 mm Hg (1.77 kPa), with a range of 10.3 to 15.7 mm Hg (1.37 to 2.09 kPa). At 8400 m, the mean arterial oxygen content was 26% lower than it was at 7100 m (145.8 ml per liter as compared with 197.1 ml per liter). The mean calculated alveolar–arterial oxygen difference was 5.4 mm Hg (0.72 kPa).

Conclusions The elevated alveolar–arterial oxygen difference that is seen in subjects who are in conditions of extreme hypoxia may represent a degree of subclinical high-altitude pulmonary edema or a functional limitation in pulmonary diffusion.

Source Information

From the Centre for Altitude, Space, and Extreme Environment Medicine, University College London Institute of Human Health and Performance, London.

Drs. Grocott and Martin contributed equally to this article.

Address reprint requests to Dr. Grocott at the Centre for Altitude, Space, and Extreme Environment Medicine, University College London Institute of Human Health and Performance, 1st Fl., Charterhouse Bldg., Archway Campus, Highgate Hill, London N19 5LW, United Kingdom, or at mike.grocott{at}ucl.ac.uk.

Full Text of this Article

Related Letters:

Blood Oxygen on Mount Everest
Daley M. R., Hilberath J. N., FitzGerald D. J., Tasker R. C., de Vries A. P.J., Berend K., Hager A., Grocott M. P.W., Martin D. S., Levett D. Z.H.
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N Engl J Med 2009; 360:1908-1910, Apr 30, 2009. Correspondence

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