Pushing the Limits of Hypoxia

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Picture of Gene Macogay, MSc, RRT, RRT-ACCS
Gene Macogay, MSc, RRT, RRT-ACCS

Registered Respiratory Therapist since 2010. Master of Science in Respiratory Care Leadership from Northeastern University. Still practicing bedside prn and working as full-time as the Director of Clinical Education at St. Petersburg College in Florida. Interests include mechanical ventilation, fundamentals of respiratory care and digging into research articles. My favorite part of my job is helping people discover their potential in this field.

The Pre-brief

Climbing Mt. Everest without supplemental oxygen is a feat that pushes the limits of human tolerance to the brink of death as a result of hypobaric hypoxia. However, nearly 200 have done it. Let’s explore…

Mt. Everest, the world’s highest peak above sea level, stands at 29,029 ft. In 2007, a group of climbers summited the mountain without the use of supplemental oxygen. Acclimatization is the term used to describe the incredible adaptive response of those exposed to prolonged and extreme environmental hypoxia.

So, what happens?

Dramatic decreases in partial pressure of oxygen (PaO2) are directly proportional to the decrease in barometric pressure associated with an increase in altitude. The barometric pressure at the peak of Mt. Everest is 253 mm Hg. However, subjects studied by Grocott et al. were able to maintain arterial oxygen saturation (SaO2) levels relatively well (group mean of 54%) in spite of a group mean PaO2 of 24.6mm Hg. It was theorized that this was due to the characteristics of the oxygen-hemoglobin dissociation curve and respiratory acclimatization (increase in hypoxic ventilatory response) causing a decrease in partial pressure of carbon dioxide (PaCO2) (group mean 13.3 mm hg). The mean pH of the group studied was 7.53, indicating a respiratory alkalosis. This, coupled with increases in hemoglobin concentration (group mean 19.3 g/dl), assured that arterial oxygen content (CaO2) was maintained until subjects reached over 23,000 ft. 

The alveolar-arterial oxygen difference was calculated as a mean of 5.4 mm Hg. This represented near normal differential and minimal diffusion impairment. Despite chronic hypoxic conditions, none of the subjects exhibited hyperlactatemia. The group mean was 2.2 mmol/liter. This suggests that increased lactate may have been used as a fuel source due to extreme conditions. 

Conclusion 

Understanding the numerous mechanisms by which the human body adapts and compensates for extreme conditions can be insightful for those treating critically ill patients. Studying the limits of hypoxic tolerance can give guidance to directed interventions that may better benefit patients.

The Debrief

  • The human body’s ability to adapt and compensate in adverse conditions is nothing short of amazing!
  • There is a more to blood gases than pH, PaO2, PaCO2, and HCO3
  • Hemoglobin matters
  • Look at the whole picture

References

  1. Grocott, M. P. W., Martin, D. S., Levett, D. Z. H., McMorrow, R., Windsor, J., & Montgomery, H. E. (2009). Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest. New England Journal of Medicine, 360(2), 140–149. https://doi.org/10.1056/nejmoa0801581

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