Oximetry, Yes Please!
Oximetry is yet another vital sign, expressed by a single number known as SpO2. This is the percentage measurement of haemoglobin linked to oxygen and for this reason is usually denoted using the symbol SpO2.
Everyone, not just doctors, knows how important it is to be aware of her or his body weight, temperature, heart rate, arterial pressure and respiratory rate. These are all vitals which supply a simple number to measure our state of health. However few people are aware of their blood oxygen level.
Measuring another vital sign: oximetry
Oxygen is largely transported by the haemoglobin molecules present in the red blood cells. It can be said without exaggeration that when the haemoglobin is very low, as in acute anaemia, a risk of instant death exists! In the reality of our organism, haemoglobin molecules cannot always transport their maximum load. On the basis of our state of health, SpO2 is at best 99%.
Haemoglobin and its ability to bond to blood oxygen
Each haemoglobin molecule is like an automobile with a load capacity of 4 passengers, represented by the molecules of oxygen entering the lung at each breath. If all the haemoglobin molecules could manage to load 4 oxygen molecules, they would be at maximum capacity: i.e. the SpO2 would be 100%. Normal SpO2 values are comprised between 95–99%. When an individual has respiratory problems due to lung, cardiac or neurological pathologies, this percentage falls, with values of < 95%. The cause of the reduction will indicate the amount of the deficit.
How the Oximeter functions
The Oximeter calculates the percentage of oxygenated haemoglobin (SpO2) by measuring the variations signalled in a two-wavelength light beam (red and infrared) crossing a part of the body characterised by a good arterial flow (such as the fingers or toes and the earlobes). While it goes without saying that the Oximeter should be used with patients having respiratory symptoms such as shortness of breath, its use is less obvious, especially, in apparently asymptomatic individuals when a respiratory, cardiac or neurological pathology is suspected.