A Comparison of Pulse Oximetry with Invasive Mixed Venous Blood Oxygen Saturation Monitoring

Abstract

Pulse oximetry is a useful method for measuring arterial haemoglobin oxygen saturation clinically under both stable and rapidly changing conditions. It also provides a possibility for continuous non-invasive monitoring. Figure 5.1 illus- trates the variables that influence arterial oxygen saturation and it will be seen that they are predominantly pulmonary. Thus pulse oximetry can be regarded as a method that above all monitors the ability of the lungs to oxygenate the blood. There must be adequate perfusion if the sensor is to be effective either on the ear lobe or on the finger. The nasal septum might offer a location with adequate perfusion if the ear lobe or finger perfusion is inadequate. Thus while pulse oximetry is valuable in assessing respiratory function, sometimes it may be less effective in assessing tissue oxygenation, for example when cardiac output is low.