Pulse Oximetry Health Information

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Pulse Oximetry Health Information

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Pulse Oximetry, Part 6

Principles of modern pulse oximetry, cont.
Arterial partial pressure of oxygen / Arterial oxygen saturation

The relationship between the arterial partial pressure of oxygen (PaO2) and the oxygen saturation is described by the haemoglobin-oxygen dissociation curve (see figure 1). The sigmoid shape of this curve facilitates unloading of oxygen in the peripheral tissues where the PaO2 is low and oxygen is required for respiration. The curve may be shifted to the left or right by various patient characteristics e.g. recent blood transfusion, pyrexia.

A pulse oximeter consists of a peripheral probe, together with a microprocessor unit, displaying a waveform, the oxygen saturation and the pulse rate. Most oximeters also have an audible pulse tone, the pitch of which is proportional to the oxygen saturation - useful when one cannot see the oximeter display.

The probe is placed on a peripheral part of the body such as a digit, ear lobe or the nose. Within the probe are two light emitting diodes (LED's), one in the visible red spectrum (660nm) and the other in the infrared spectrum (940nm). The beams of light pass through the tissues to a photodetector. During passage through the tissues, some light is absorbed by blood and soft tissues depending on the concentration of haemoglobin. The amount of light absorption at each light frequency depends on the degree of oxygenation of haemoglobin within the tissues.

Back: Practical Applications Also See: Pulse Oximeters Next: Principles of modern pulse oximetry, cont.
  1. Update in Anaesthesia. Practical Procedures, Issue 11 (2000) Article 4. Dr E Hill, Dr MD Stoneham, Nuffield Department of Anaesthetics, Oxford Radcliffe NHS Hospitals Headington, Oxford OX3 9DU