Therefore, your PR interval may or may not be short and I wouldn't worry until you receive a full report. The PR interval is short in children and lengthens as we get older. A normal value in adults is 120 to 200 milliseconds. It is however shorter than 120ms in approximately 2 to 4% of the adult population.
It is SaO2 that measures oxygen saturation of hemoglobin, and it should be clear that it depends on the partial pressure of arterial oxygen. If PaO2 drops, there's less dissolved oxygen, and therefore less saturation of hemoglobin with oxygen.
Step 1 Identify the Pao2 and determine whether it is below or within normal range. The normal predicted Pao2 is dependent on the patient's age, FIO2, and barometric pressure. In general, a Pao2 lower than 80 mm Hg in a patient younger than 60 years of age is abnormal, and hypoxemia is occurring.