Oxygen is vital to system and organ function in our bodies. In order to be carried around the body, molecules of oxygen attach to the haemoglobin proteins in red blood cells. The amount of oxygen (measured as a %) in haemoglobin proteins is called ‘oxygen saturation’ and this percentage can be determined using pulse oximetry. The values from pulse oximetry are useful as they tell us how much oxygen is actually reaching the different organs and systems in the body. Pulse oximetry uses devices called pulse oximeters that attach to an area on the patient where blood flow can be measured (most commonly on the finger). Light is then shone through the skin it is positioned on and a detector on the other side measures the amount of light that makes it through. The amount of absorbed light is indicative of the oxygen concentration and as such, a pulse oximeter does not directly measure oxygen saturation but rather closely estimates it. Normal levels of oxygen saturation are between 95-100%