A child's organs and tissue require a constant supply of oxygen to function normally. Red blood cells (RBCs) contain an oxygen-transporting protein called hemoglobin, which picks up oxygen in the lungs and delivers it the rest of the body. When the hemoglobin within RBCs is carrying the maximum amount of oxygen it can hold, it's said to be saturated. The oxygen saturation test measures the percentage of hemoglobin in the RBCs that is fully saturated. A normal oxygen saturation level in healthy child breathing room air is typically 96 percent or higher.
Oxygen saturation is usually measured with a pulse oximeter. A painless clip is attached to the child's finger, toe or ear lobe. One side of the clip shines red and infrared light through the area. The other side senses the amount of light that passes through. The machine performs an internal calculation and displays the oxygen saturation level. This noninvasive measurement is often sufficient for monitoring purposes. In certain medical circumstances, however, direct measurement of the oxygen saturation is preferred. This is accomplished by drawing a sample of arterial blood, which is then tested in the laboratory.
Oxygen saturation generally reflects how well a child's lungs and circulatory system are working together to supply oxygen to the body. Both the lungs and circulatory system must be functioning normally for a child to have a healthy oxygen saturation level. Conversely, problems with the heart, circulatory system or lungs can cause an abnormally low oxygen saturation level, which typically requires urgent medical attention to prevent possible damage to the body organs and tissues caused by lack of oxygen.
An oxygen saturation of 95 percent or lower in a child usually indicates a breathing or circulatory problem. Breathing problems account for most cases of temporary decreases in oxygen saturation among children. Common examples include an asthma attack or pneumonia. Less commonly, circulatory system problems are to blame, such as a congenital heart malformation or shock caused by blood loss or a severe infection. Supplemental oxygen administered through a mask or nasal prongs often helps relieve a short-term decrease in oxygen saturation.
Continual oxygen saturation monitoring with a pulse oximeter is commonplace during hospital stays and at home for children with chronic lung diseases, such as cystic fibrosis. Pulse oximetry is simple and painless, and is an efficient method for detecting a decrease in oxygen saturation before complications develop. Home-use pulse oximeters are widely available for monitoring oxygen saturation levels at rest, during exercise or when breathing symptoms flare up. Your doctor will clarify when and how to use the pulse oximeter, and what to do if the oxygen saturation falls.
Warnings and Precautions
If you are monitoring your child's oxygen saturation at home, contact your doctor right away if it falls to a critical level. Talk with your doctor if you're unsure what level requires medical attention or at-home treatment. If your child's oxygen saturation falls below 95 percent and you cannot reach your doctor right away, seek emergency medical care. Also seek immediate medical care if your child is struggling to breathe, turns blue or pale, seems confused, inattentive or agitated, or loses consciousness -- regardless of the oxygen saturation level.
Reviewed and revised by: Tina M. St. John, M.D.