How to Read Pulse Oximetry Results

Pulse oximeters, whether they are the large units you see in hospitals, or the portable ones that you can simply clip on a finger, are interpreted with a standard value. There might be a variation in their size, but like most medical equipment, their results are always compared with a value that is considered normal in the field of medicine.

Oxygen that is inhaled from the atmosphere diffuses through the lungs and into the bloodstream to be used up by body tissues for energy. In the blood, most of the oxygen is bound to the hemoglobin component of a red blood cell while a few are dissolved in plasma. A pulse oximeter reads the concentration of oxygen bound to hemoglobin in the blood by shining infrared and red light through a translucent part of the body and measuring the ratio of light reflected and light absorbed by oxygenated and deoxygenated hemoglobin. Hence, it becomes a good indicator of the oxygenation status of a person, especially hypoxemia.

Pulse oximeters read the value of the saturation of peripheral oxygen or SpO₂ or simply the oxygen saturation of the peripheral blood. The value is read in percentage form. In most literature, the accepted normal value of a pulse oximeter reading is between 95-100%. Anything that falls below 95% is already categorized as hypoxemia. That’s why it would be necessary to set the alarm (if any) at 95%. When the reading is at 85% and below, the person is already at a critical level. Cerebral hypoxia (low oxygen level in the brain) may follow in a few minutes and cause irreversible brain damage. Several vital organs might also be affected. The person warrants immediate treatment and oxygenation.

Oxygen saturation can never be more than 100%. But the results may display 100% and still exhibit signs of hypoxia. This happens in cases of anemia because of a low blood hemoglobin level and carbon monoxide poisoning.

Reading a pulse oximeter is easy, but the accuracy of the results rests on several factors, limitations, and medical conditions. Hence, before the interpretation of a result, it is essential to make a quick but thorough assessment of the person’s condition.