The result from the blood test, which is called an arterial blood gas
(ABG), of 55 mm Hg is a measure of gas
pressure, like the pressure of air in your tires. This should be 90 to 100 mm Hg at sea level, so your result of 55 mm Hg is abnormally low. This discrepancy suggests that one of these measurements is wrong. Both the oximetry and the arterial blood gas determinations should be repeated, before the final decision is made on your oxygen needs.