A strategy for determining arterial blood gases on the summit of Mt. Everest

BACKGROUND: Climbers on the summit of Mt. Everest are exposed to extreme hypoxia, and the physiological implications are of great interest. Inferences have been made from alveolar gas samples collected on the summit, but arterial blood samples would give critical information. We propose a plan to insert an arterial catheter at an altitude of 8000 m, take blood samples above this using an automatic sampler, store the samples in glass syringes in an ice-water slurry, and analyze them lower on the mountain 4 to 6 hours later. RESULTS: A preliminary design of the automatic sampler was successfully tested at the White Mountain Research Station (altitude 3800 m – 4300 m). To determine how much the blood gases changed over a long period, rabbit blood was tonometered to give a gas composition close to that expected on the summit (PO(2 )4.0 kPa (30 mmHg), PCO(2 )1.3 kPa (10 mmHg), pH 7.7) and the blood gases were measured every 2 hours for 8 hours both at sea level and 3800 m. The mean changes were PO(2 )+0.3 to +0.4 kPa (+2 to +3 mmHg), PCO(2 )0 to +0.13 kPa (+1 mmHg), pH -0.02 to -0.04, base excess -0.7 to -1.2 mM. In practice the delay before analysis should not exceed 4 to 6 hours. The small paradoxical rise in PO(2 )is presumably caused mainly by contamination of the blood with air. CONCLUSION: We conclude that automatic arterial blood sampling at high altitude is technically feasible and that the changes in the blood gases over a period of several hours are acceptably small.