Pulse oximetry is a simple, non-invasive method of monitoring the percentage of hemoglobin (Hb) which is saturated with oxygen.  The pulse oximeter consists of a clip attached to the patient's finger or ear lobe, which is linked to a computerized unit.  The unit displays the percentage of Hb saturated with oxygen.  Some units may also have an audible signal fo reach pulse beat, a calculated heart rate and/or graphical display of the blood flow past the clip.

How does an oximeter work?
A source of light emitted in two wavelengths (650 nm and 805 nm) by the clip is partly absorbed by Hb, in amounts which differ depending on whether it is saturated or desaturated with oxygen.  The processor computes the proportion of saturated Hb by calculating the absorption at the two wavelengths.

Oximeters are accurate in the range of oxygen saturations of 70-100 percent, but less accurate under 70 percent.

Pulse oximeter readings may be affected by:  body temperature; cold extremities; puffy, swollen fingers from edema; heart conditions; blood pressure; peripheral vascular disease; venus congestion; bright overhead lights; shivering; Hb mixed with carbon monoxide; methylene blue used in surgery; and nail polish, acrylic nails or thick nails may cause false low readings, although the units are not affected by jaundice, dark skin or anemia.

What do the numbers mean?
Oxygen saturation levels should be between 95 percent and 100 percent. If you have an underlying respiratory or lung condition, normal oxygenation for you may be different from someone else.  Normally, an oximetry reading is expected to be greater than 92 percent.  Pulse oximetry offers a guideline for assessing oxygen status.  If your saturation is less than 92 percent, your doctor may order additional tests.

The most common physical symptoms associated with a decrease oxygen level include:

• Shortness of breath
• Breathing at a fast rate
• Increase heart rate
• Restlessness
• Paleness in skin tone
• Bluish color around lips and under nail beds
• Confusion

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