Oxygenated blood appears as a brighter red, which means that red wavelengths are reflected back towards the device. The opposite is true for deoxygenated blood, causing it to absorb more red light and instead, scatter infrared light.
To put it simply, by measuring the absorbance of two different wavelengths of light, red light and infrared light, the pulse oximeter can gauge how much of the blood is oxygenated.
A pulse oximeter reading of anywhere from 95% and above is often considered an acceptable and healthy value. A percentage below that however, puts a patient at risk of hypoxemia: a deficiency of oxygen in their blood.
Hypoxia is a general term used to describe oxygen deficiency in tissues and organs following hypoxemia. It causes a multitude of health issues, most commonly shortness of breath, but can also be linked to headaches, dizziness, and other conditions. Hypoxemia’s effects on the respiratory system have been of particular interest recently because of its connection to COVID-19.
Pulse oximeters have become a popular device to detect coronavirus-related hypoxia because of the phenomena of silent hypoxemia: one that does not present any symptoms, including the telling sign of shortness of breath.
There are a multitude of theories as to why silent hypoxemia emerges in COVID-19 patients, with ongoing research to find the true cause. One such theory is that the virus causes the production of thrombi, or blood clots, in pulmonary vessels to cause inefficient oxygen exchange between the lungs and the blood.
Silent hypoxemia presents medical concern based on the fact that abnormally low oxygen levels that go undetected, and therefore untreated, may cause long-term negative effects on a patient’s body.
Patients that are deemed to be at risk of hypoxia, but are healthy enough to warrant against hospitalization, may be sent home with a pulse oximeter to monitor their health. Upon presenting oxygen saturation levels that indicate hypoxemia, they are advised to seek medical attention.