Which arterial blood gas value is most important when determining the effectiveness of oxygen therapy if a client is receiving supplemental oxygen?

When you are determining whether the patient is receiving enough oxygen, the most important value is the partial pressure of oxygen. It should be about 100 in a normal person. Blood is drawn from an artery so it is freshly oxygenated giving us a measure of the oxygenating power of the lungs.

Even slight changes in the breathing efforts are manifested in the arterial blood gases which makes it a reliable test for detecting the pH of the blood as well as the supplemental oxygen. When the oxygen saturation starts to decrease the patient is unable to sustain his breathing on normal atmospheric oxygen and requires supplemental oxygen. If it does not improve, he needs ventilator support.