Oxygen saturation refers to the amount of oxygen carried in the red blood cells. Harvard Medical School explains that 95 to 100 percent of the red blood cells should contain oxygen as they pass through the lungs. Medical professionals use information on oxygen saturation level to determine if a patient has a problem with the heart or lungs.
Definition
Dr. Ken Miller of the University of California, Irvine, defines a pulse oximeter as a device that measures the saturation of hemoglobin with oxygen. Hemoglobin is a protein molecule that carries oxygen in the red blood cells. Medical professionals use this device by attaching it to the fingertip of a patient in the hospital or physician’s office.
Features
The pulse oximeter consists of light emitting diodes and a photodiode. These components emit different types of light to help determine oxygen saturation. The oximeter also has a clip for attachment to a patient’s finger. Some hospitals connect pulse oximeters to heart monitors so medical staff can quickly view the oxygen saturation level of a patient in distress.
Function
Oxygenated hemoglobin absorbs light differently than hemoglobin that has less oxygen than normal. Oxygenated hemoglobin absorbs infrared light, whole deoxygenated hemoglobin absorbs red light. The photodiode receives the light signals and calculates the amount of red light compared to infrared light. Using this ratio, the pulse oximeter determines an approximate oxygen saturation level.
Benefits
The use of a pulse oximeter has several benefits in emergency and acute care settings. In cases of trauma or serious illness, using a pulse oximeter allows medical professionals to quickly assess the status of a patient. Patients with low oxygen saturation levels can receive the oxygen they need to prevent serious complications. In the operating and recovery rooms, the use of the pulse oximeter helps medical professionals determine if a patient is progressing normally through a procedure and the initial recovery period.
Accuracy
Pulse oximeters have fairly good accuracy when estimating oxygen saturation levels of 80 percent or above. The oximeter has a memory that contains a chart of oxygen saturation values. Researchers derived these values by administering hypoxic mixtures to human volunteers. Hypoxic mixtures reduce the amount of oxygenated hemoglobin. Because it would be unethical to subject human volunteers to oxygen levels below 80 percent, the oximeter memory bank does not have stored values below this level. Dr. Vijaylakshmi Kamat explains that accuracy below oxygen saturation levels of 75 to 80 percent cannot be determined.
Dissolved Oxygen
Since the pulse oximeter cannot determine the amount of oxygen dissolved in the blood plasma, it does not provide a complete picture of a patient’s oxygen level. Doctors may use additional tests, such as a carbon dioxide blood test, to determine if a patient needs oxygen administration.
