Pulse oximetry (or pulse oxymetry) is a non-invasive method allowing the monitoring of the oxygenation of a patient’s hemoglobin. Pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient’s blood and changes in blood volume in the skin, producing a photoplethysmograph. A blood-oxygen monitor displays the percentage of arterial hemoglobin in the oxyhemoglobin configuration. Portable battery-operated pulse oximeters are also available for home blood-oxygen monitoring. Pulse oximeter is often attached to a medical monitor so hospital staff can see a patient’s oxygenation at all times. Most digital healthcare monitors also display the heart rate.

Pulse Oximetry: Operation of Pulse Oximeter

A sensor is placed on a thin part of the patient’s body, usually a fingertip or earlobe, or in the case of an infant, across a foot. Light with red wavelengths and light with infrared wavelengths is sequentially passed from one side to a photodetector on the other side. Changing absorbance of each of the two wavelengths is measured, allowing determination of the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) fingernail polish. Based upon the ratio of changing absorbance of the red and infrared light caused by the difference in color between oxygen-bound (bright red) and oxygen-unbound (dark red or blue, in severe cases) blood hemoglobin, a measure of oxygenation (the per cent of hemoglobin molecules bound with oxygen molecules) can be made.

Advantages of Pulse Oximeter

  • A pulse oximeter is useful in any setting where a patient’s oxygenation is unstable, including intensive care, operating, recovery, emergency and hospital ward settings, pilots in unpressurized aircraft, for assessment of any patient’s oxygenation, and determining the effectiveness of or need for supplemental oxygen.
  • A patient’s need for oxygen is essential to life; no human life thrives in the absence of oxygen (cellular or gross). Although pulse oximetry is used to monitor oxygenation, it cannot determine the metabolism of oxygen, or the amount of oxygen being used by a patient.
  • Because of their simplicity and speed, pulse oximeters are of critical importance in emergency medicine and are also very useful for patients with respiratory or cardiac problems, especially COPD, or for diagnosis of some sleep disorders such as apnea and hypopnea.
  • Portable battery-operated pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise. Some portable pulse oximeters employ software that charts a patient’s blood oxygen and pulse, serving as a reminder to check blood oxygen levels.

Disadvantages of Pulse Oximeter

Pulse Oximetry is not a complete measure of respiratory sufficiency. Pulse oximetry measures solely of oxygenation, not ventilation, and it is not a substitute for blood gases checked in a laboratory because it gives no indication of base deficit, carbon dioxide levels, blood pH, or bicarbonate HCO3-concentration.