Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest

Michael Grocott and his colleagues were part of the prodigious Caudwell Xtreme Everest Research Expedition that took a team of climbers and scientists to Mount Everest, in order to learn more about high altitude medicine and physiology. Their work is being published as the data are analyzed. In an article entitled "Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest" (New England Journal of Medicine 2009;360:140-9), Grocott's team measured arterial blood gases in climbers breathing ambient air (not supplemented with oxygen) during their ascent to and descent from the summit of Mt. Everest. Measuring arterial blood gases provides direct determination of the partial pressures of oxygen and carbon dioxide, as well as pH (measure of acid-base balance). This involves taking a sample of blood directly from an artery. The team also measured hemoglobin (carried in red blood cells) and lactic acid levels in the blood samples. Finally, they calculated oxygen saturation, which indicates the degree to which red blood cells take up oxygen, as opposed to the precise amount of oxygen present in the blood.

Their determinations showed some interesting findings. As one might expect, the partial pressure of oxygen declined with increasing altitude. However, the hemoglobin (oxygen-carrying molecule) concentration in the blood rose with increasing altitude, allowing the oxygen content of arterial blood to remain at or above sea-level values until the climbers reached an elevation of 7100 meters (23,294 feet). At 8400 meters (27,559 feet) altitude, the mean arterial oxygen content was 26% lower than it was at 7100 meters. In conjunction with other observations, the authors concluded that in addition to the extreme hypoxia (low oxygen in the bloodstream) noted in the climbers at extreme altitude, the climbers may also have suffered from a degree of high altitude pulmonary edema (HAPE: fluid in the lungs) or some limitation in the ability of oxygen to move from the air spaces within the lungs into the bloodstream.

Very few persons (less than 4%) summit Mt. Everest without using supplemental oxygen. The summit of Mt. Everest is at 8848 meters (29029 feet), which is considered to be close to the limit that a person acclimatized to high altitude can tolerate in a manner compatible with survival, while not breathing supplemental oxygen.

Weather conditions precluded this particular research expedition's ability to obtain arterial blood samples at the summit of Mt. Everest. The samples obtained at 8400 meters were obtained from within a small erected shelter during descent at a location known as "the Balcony." These samples demonstrated the remarkable adaptive response (acclimatization) achieved by the climbers. Whereas a nonacclimatized person transported suddenly to such an altitude would become unconscious within a few minutes from lack of oxygen, these climbers were thinking clearly. It was noted by the investigators that supplemental oxygen had been used intermittently during the climb, but that the arterial blood samples were obtained after a 20-minute rest period in which there was no supplemental oxygen use. The effect upon hyperventilation posed by intermittent supplemental oxygen use is also similarly not definitively resolved.

The authors wisely make comment about the relevance of this sort of research to lowlanders. It may be helpful to understand the human tolerance for limits of hypoxia, and the effects of supplementing red blood cell oxygen-carrying capacity for persons with respiratory failure or other critical illnesses.

Photo by Mathias Schar

Tags: arterial blood gas, blood gas, oxygen, Mt. Everest, climbers, healthline