ABSTRACT
Haemoglobin saturation can be measured directly by arterial blood gas analysis, but is more conveniently measured by the use of a pulse oximeter. D?O2 is the rate at which oxygen is delivered to the tissues, given by the product of arterial blood oxygen concentration and cardiac output. Reduced haemoglobin is bluish in colour, giving the hypoxic patient a cyanotic appearance when severe. Well-oxygenated blood is cherry red. Pulse oximetry quantifies arterial blood colour by its light absorption, measured during arterial pulsation. The waveform is important in providing a means of ensuring good transduction of the arterial pulse. A normal waveform has a dicrotic notch on the downslope of the wave, as seen in an arterial pressure waveform. A low saturation reading should prompt a check of the pulse waveform. If low saturation is measured in the presence of a good waveform, real hypoxaemia must be assumed until proven otherwise, and poor transduction should not be implicated.
