Oxygen Saturation

Oxygen saturation is the percentage of hemoglobin in the blood that is carrying oxygen. It is usually measured with a pulse oximeter clipped to a finger and recorded as SpO2. Healthy people at sea level typically read about 95 to 100 percent; lower readings can mean the lungs are not transferring oxygen well.

Origin

Pulse oximetry was invented in Japan in the 1970s by the engineer Takuo Aoyagi and spread into hospitals in the 1980s. It is now a routine vital sign at almost every medical visit.

Significance in Asbestos Context

In asbestosis, scarring thickens the walls of the air sacs so oxygen passes into the blood less easily, and saturation may drop first during exercise or sleep. A resting or exercise saturation of 88 percent or lower is the usual threshold for prescribing supplemental oxygen. Pleural effusions, mesothelioma, lung cancer and treatment side effects such as pneumonitis can also lower it. Pulse oximeters are convenient but imperfect: readings can be off with cold hands, poor circulation, nail polish or movement, and the FDA has warned that they can overestimate oxygen levels in people with darker skin. A blood test from an artery (an arterial blood gas) is more accurate when precision matters. Because the number appears in nearly every chart, a series of saturation readings over time is a simple, objective record of declining lung function in a medical timeline.

Example Sentence

His resting oxygen saturation had slipped from 96 percent to 91 percent over two years, and on exertion it dropped to 87 percent.

Related Terms

Hypoxia, Supplemental Oxygen, Six-Minute Walk Test, Diffusing Capacity (DLCO), Asbestosis, Pulmonary Function Test (PFT), Dyspnea, Cor Pulmonale

Notes

• A home pulse oximeter can be useful, but ask your doctor what numbers should prompt a call.
• Warm your hands and sit still for a minute before taking a reading.
• Readings taken during exercise or sleep can matter more than resting ones in early lung disease; ask whether you need them.