Blood oxygen saturation levels show how much oxygen is being carried by red blood cells. For people with healthy lungs, levels from 95 to 99% are normal. Levels above 99% are rare without the use of supplemental oxygen. Levels below 95% indicate hypoxemia, which often includes symptoms such as shortness of breath, chest pain, rapid heartbeat, headache, or confusion.
One way to measure blood oxygen saturation is with an arterial blood gas (ABG) test. For this test, a nurse or doctor draws a sample of blood from an artery and places it in an analyzer. The equipment measures partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), bicarbonate (HCO3), oxygen saturation (O2 Sat), and pH. This method is effective but invasive, can take several minutes to complete, and may be uncomfortable for the patient.
A noninvasive method for measuring blood oxygen saturation is pulse oximetry. For this test, a nurse or doctor–or even the patient–places a sensor on a finger, toe, or earlobe. The oximeter sends two wavelengths of light through the skin, measures how much is absorbed, and calculates the result, and shows it on a display. This method is fast, easy, and comfortable for everyone.
Note: Nonin offers pulse oximeters with PureSAT® technology in fingertip, handheld, and tabletop models. Nonin also provides external signal processors and internal circuit boards with full pulse oximetry functionality for integration in monitoring systems by other manufacturers. The Nonin equipment used in this study was an OEM III module with an 8000AA sensor.
Researchers at the Hypoxia Research Laboratory of the University of California San Francisco conducted a study to compare the accuracy of these two methods. They tested results from Nonin PureSAT® signal processing technology and a co-oximeter (blood gas analyzer) during patient motion. Co-oximetry is considered the gold standard of blood analysis. Measured by ABG, the normal range of PaO2 is 80 to 100 millimeters of mercury (mmHg). Measured by pulse oximetry, the normal range of SpO2 is 95 to 99%.
Researchers induced hypoxia symptoms in each of 12 subjects, following a standard protocol of rapid arterial desaturation, and simulated motion with tapping and rubbing by a mechanical fixture. They conducted the same test twice, measuring blood oxygen levels by both methods at each of five plateaus. As an additional reference, the researchers tested a pulse oximeter from another well known manufacturer. This second model was also marketed as motion-tolerant.
ABG testing is recognized as the most accurate method for measuring blood oxygen levels. For this study, ABG readings provided a baseline to which the noninvasive measurements could be compared. To learn more, see how closely the two pulse oximeters matched the ABG readings.