A pulse oximeter is a medical device that measures heart rate and the oxygen level in the blood, expressed as the percent of oxygen saturation. Pulse oximeters operate by shining light through the skin to the blood vessels below. These devices are routinely used in many health care settings and are available over the counter. A high oxygen saturation -- close to 100 percent -- indicates that the red blood cells are fully loaded with oxygen from the lungs.
Turn on the pulse oximeter by firmly pressing the power button. The screen should light up almost instantly.
Place the sensor -- the part that opens and closes like a clothespin -- on any finger, with the sensor screen above the fingernail. If the sensor doesn't have a screen, run the cable along the back of the finger or hand. Don't use the thumb because readings are less reliable than finger readings.
Wait quietly while the pulse oximeter acquires a signal. This may take 10 seconds or more, depending on the device and the conditions. Excessive movement during measurement can decrease the accuracy of the result or may cause an error message.
Look at the display to see the heart rate, usually indicated with a heart or pulsing light. The percent of oxygen saturation is typically indicated by the symbol "SpO2." Many devices also have a pulse tone that beeps in time with the heart rate.
Leave the sensor on for continuous monitoring. The sensor can become uncomfortable or cause pressure sores if left on the finger too long. Check and/or move the sensor at least every two to four hours. If only a single measurement is required, remove the sensor and press the power button to turn off the device.