A-a gradient, a/A ratio, and P: F ratio - are all different views of the same item. These formulas do not have a complete view of oxygenation. Oxygenation is a huge topic, and there are more common values that we use:

• How well is the patient saturating?

• Is there dyspnea?

• How do the lungs sound (auscultation) or look (POCUS)?

• Where is the patient on the OHCD?

• What does the ABG show?