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Pulse oximetry and pulse oximetry appeared in medicine relatively recently. A pulse oximeter is a clip-like device that fits over your index finger. How does a pulse oximeter work? What is pulse oximetry for?

The pulse oximeter(measuring device) is usually put on the finger, where a special sensor measures the absorption of radiation from the transmitter by red blood cells.

Pulse oxymetryis a branch of modern research that allows you to painlessly and non-invasively measure the heart rate and the degree of blood saturation with oxygen, i.e. saturation ( saturation is the saturation of the liquid with gas).

The result of the test performed with the camera is presented as a percentage. It represents the amount of hemoglobin that is saturated with oxygen.

The pulse oximeter sensor can be attached not only to the finger of the hand, but also to the toe, the auricle, the nose wing, and the forehead. In neonates, the sensor is placed on the foot or wrist.

Pulse oximeter - what is it?

Simply put, it is an electronic device consisting of two important parts, i.e. the central unit and the sensor.

The sensor is made of a red and infrared light emitter and a photo detector.

The test measures the absorption of radiation from the transmitter by the erythrocytes (red blood cells) in the capillaries.

Pulse oximeter - how does it work?

After selecting the place on the body where the camera sensor will be placed, it will be launched. If the hands or feet are cold, warm them up beforehand to restore normal blood flow in the limb. When the hands are cold, the blood flows slower, and this may cause false results.

The principle of transmission spectrophotometry is used to determine the oxygen saturation of arterial hemoglobin. The emitted radiation is to some extent absorbed by the blood in the blood vessels.

The photo detector measures the returning signal. The measured signal consists of two components: constant and variable (so-called pulsating). It is this component that describes the absorbance of pulsating arterial blood.

The test result is presented as a percentage. It represents the amount of hemoglobin saturated with oxygen, i.e.oxyhemoglobin.

The device also measures the heart rate (pulse).

Pulse oximeter - what is it for?

The determination of blood saturation with oxygen is an extremely important test that allows you to counteract respiratory failure developing in a patient. It is usually used in hospitalized patients.

The test should also be performed:

  • in patients with respiratory failure
  • when controlling vital functions of mother and fetus
  • when performing bronchoscopy
  • when qualifying the patient for oxygen therapy
  • during procedures performed under general anesthesia
  • in the postoperative period
  • with each child anesthesia
  • in every patient who is in serious condition
  • for ventilation of one lung

Pulse oximeter - saturation results

The blood oxygen saturation is at the level of 95-98%.

In people over 70 years of age, the correct saturation is considered to be 94-98%.

The oxygen saturation of arterial blood should reach the level of 98-100% during the oxygen therapy.

For smokers, the results will be slightly lower compared to non-smokers, but still the oxyhaemoglobin percentage will be above 90.

Abnormal blood oxygen saturation is below 90%, which may indicate severe respiratory failure.

It should be remembered, however, that the oximetry measurement applies only to the saturation of hemoglobin with oxygen, not to the oxygen metabolism at the cellular level. Thus, it may happen that the saturation is high but the oxygen value is decreased at the cell level.

Pulse oximeter - what affects the result?

There are many elements that can significantly affect the measurement of arterial hemoglobin oxygen saturation. They include:

  • factors that impair peripheral blood flow, i.e. blood flow in the extremities
  • low tissue perfusion, i.e. blood flow through the tissue
  • cool place of measurement
  • uncontrolled patient movements, muscle tremors
  • abnormal hemoglobin, e.g. methemoglibin, a form of hemoglobin that is formed as a result of oxidation in the course of poisoning with chemical substances (acetylsalicylic acid, sulfonamides)
  • presence of carboxyhemoglibine, which is formed as a result of carbon monoxide poisoning, or colloquially speaking, carbon monoxide
  • fluorescent light increases the saturation values ​​
  • diseases of the nail plate (mycosis) and in the case offemale dark nail polish
About the authorAnna Jarosz A journalist who has been involved in popularizing he alth education for over 40 years. Winner of many competitions for journalists dealing with medicine and he alth. She received, among others The "Golden OTIS" Trust Award in the "Media and He alth" category, St. Kamil awarded on the occasion of the World Day of the Sick, twice the "Crystal Pen" in the national competition for journalists promoting he alth, and many awards and distinctions in competitions for the "Medical Journalist of the Year" organized by the Polish Association of Journalists for He alth.

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