A pulse oximeter measures the oxygenation in the blood in a non-invasive way, by evaluating the percentage of hemoglobin that is saturated with oxygen in the blood. Because no blood tests are needed, the procedure is comfortable for the patient. The pulse oximeter sounds an alarm at a number set for the individual patient.
Uses
A pulse oximeter is commonly used for people during and after surgery, to ensure adequate oxygenation while under anesthesia and for people receiving oxygen therapy, to assess the effectiveness of treatment.
Method
A pulse oximeter works on the principal that oxygenated blood absorbs more infrared light and allows more red light to pass through, while less oxygenated blood absorbs more red light and allows more infrared light through, Oximetry.org states. Because red light and infrared light occur at different wavelengths, the pulse oximeter calculates absorption of light by hemoglobin in the blood to determine how much of the blood is oxygenated, Dr. S.J. Fearnley of the Torbay Hospital Anesthesia Department in the United Kingdom reports in a 1995 issue of "Update in Anaesthesia." The probe fits around a relatively translucent part of the body such as a finger, toe or earlobe.
Benefits
A pulse oximeter is painless and simple to use. Because it's difficult to visually determine hypoxemia, or low oxygen levels, until the levels drop to below 80 percent, pulse oximetry provides a continuous evaluation of oxygenation without drawing blood. Normal oxygenation stays above 90 percent, Amal Jubran of Loyola University Stritch School of Medicine in Illinois reported in the 1999 issue of "Critical Care."
Limitations
Pulse oximeters have limitations. Motion can disrupt the signal, and conditions that cause perfusion problems, such as low cardiac output, may make it hard to register a signal, Jubran states. Finger probes pick up changes in oxygenation less quickly than probes placed on earlobes. Probes can also come off, setting off false alarms. Use of certain dyes can artificially lower readings for a short time; nail polish can also lower readings artificially.
Considerations
A pulse oximeter must be properly applied and set by personnel who understand its function and the significance of low readings. Jubran reported that one survey of doctors and nurses using pulse oximetry revealed that 30 percent of physicians and 93 percent of nursing staff incorrectly identified what the pulse oximeter was measuring. Frequent false alarms can lead to complacency and lack of response to a true drop in oxygenation. Pulse oximeters don't measure carbon dioxide and so have less usefulness in people who have respiratory failure for retained carbon dioxide, notes Jubran.
