How to Read a Pulse Oximeter

Pulse oximeters are devices that are used to indirectly measure the amount of oxygen in the blood by measuring a quantity known as oxygen saturation, or SpO2. SpO2 is a measurement of the percentage of hemoglobin molecules that are bound to oxygen. Hemoglobin, the primary oxygen-carrying protein in the blood, changes color when it is bound to oxygen. By using sensors that detect the color changes in the blood due to movement of oxygen-bound hemoglobin, pulse oximeters can determine the amount of oxygen in the blood, which is useful for measuring a patient's respiratory function.

Step 1

Locate the SpO2 reading. This reading can be found on the digital readout of the pulse oximeter and will be given as a percentage, often between 90 and 100 percent. The exact location can vary depending on the type of oximeter that is being used. Some pulse oximeters will also have a bar that indicates signal strength, which is a measurement of the intensity of the signal that the sensor is generating; a high signal strength is less prone to errors. Normally, patients will have SpO2 levels between 96 and 99 percent, according to Konica Minolta Sensory Incorporated. Levels below 90 percent are generally indicative of acute respiratory failure. However, the normal range can vary from patient to patient; patients with chronic respiratory diseases may have an SpO2 level below 90 percent without having an acute respiratory problem.

Step 2

Identify the pulse rate. Pulse oximeters typically measure a patient's pulse rate in addition to his oxygen saturation. The pulse will be displayed as a two- or three-digit number, normally between 60 and 100 in an adult and higher in infants and children. It will often be displayed along with a heart shape or the letters BPM, which stands for beats-per-minute.

Step 3

Locate any other measurements on the display screen. Some pulse oximeters, such as the R Series from Zoll, also display a patient's ECG and plethysmogram. The ECG, which measures the electrical activity that the heart generates while beating, can be used to monitor cardiac function and identify arrhythmias. A plethysomogram, on the other hand, displays the changes in the amount of oxygen in the blood that occur with each pulse. These pulse oximeters generally are not available for home use.


The pulse oximeter setting for high and low readings can generally be changed at home. Do not change the settings unless your doctor suggests doing so.

If the pulse oximeter probe, which fits around the patient's finger or toe, is loose or falls off, the reading will be inaccurate.

While you can silence the monitor's alarm temporarily, it is a good idea to get in the habit of keeping it on, so you know when the heart rate or oxygen saturation level drop below normal.

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