ABSTRACT
This chapter explains the working of a pulse oximeter. The equipment consists of an electronic processor, two light-emitting diodes (LEDs) and a photodiode. Oxyhaemoglobin and deoxyhaemoglobin absorb these wavelengths of light differently; this is why arterial blood appears brighter red than venous blood to the human eye. Beer-Lambert law, which relates the attenuation of light to the properties of the material through which the light is travelling. The LEDs and the photodiode are usually arranged on either end of an adhesive strip, or on a 'clip', that is placed around a thin part of the patient's anatomy, typically a finger, an ear lobe or the forefoot of an infant. Factors that may decrease the accuracy of pulse oximetry include movement artefact, severe anaemia, and methaemoglobinaemia. The human volunteers used to construct empirical saturation tables did not have their oxygen saturations dropped below approximately 85%; hence readings below this number are extrapolated, not validated.
