OXYGEN

Clinical Scenario 1 Solution
 

An 18 year old male is brought to the recovery room following an appendectomy. He has just been extubated. He is awake and breathing normally, but his SpO₂ is 88%. You administer 60% oxygen, and after a few moments his SpO₂ increases to 99%.

What has just happened?

This is a process known as diffusion hypoxia, which is not uncommon after anesthesia with nitrous oxide. This agent is floods back into the alveoli from the blood at termination of anesthesia, along the concentration gradient, and displaces oxygen. As the partial pressure of oxygen in the alveoli has fallen, so too has the tension of oxygen in the blood. The treatment is to increase the FiO₂, which, according to the alveolar gas equation, will increase the PAO₂. Patients who hypoventilate, such as those given opioids, have increased alveolar levels of CO₂ and may require supplemental oxygen.

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