Normal oxygen saturation levels (SpO2) are between 95 to 100 percent for both adults and children. Oxygen saturation levels below 95% are considered abnormal, and the brain may be affected when SpO2 levels drop below 80 to 85 percent. Bluish discoloration of the skin or mucous membranes (cyanosis) occurs when SpO2 levels fall below 67% . However, older adults usually have slightly lower oxygen saturation levels than younger adults and children. People over 70 years of age may have oxygen levels closer to 95%, which can be normal for that age group, while normal SpO2 rates for infants and children are usually 97% and higher. It is important to note that the oxygen saturation level varies considerably based on a person’s state of health. Thus, it is important to understand both baseline readings and underlying physiology associated with certain conditions to interpret oxygen saturation levels and changes in these levels. In practice, the SpO2 range of 92–100% is generally acceptable for most clients. Some experts have suggested that a SpO2 level of at least 90% will prevent hypoxic tissue injury and ensure client safety.