Many patients with COVID-19 disease have low oxygen levels even when they are feeling well. Low oxygen levels can be an early warning sign that medical intervention is needed.
Pulse oximetry is the method that measures the percentage of blood hemoglobin carrying oxygen. Many consider it a vital sign, like blood pressure.
A beam of red light is passed through the fingertip by using a device called a pulse oximeter. Oxygen level, or saturation (SpO2), is determined by measuring how much light is absorbed as it passes through the fingertip.
Why pulse oximetry is important in COVID-19?
Normal SpO2 is usually at least 95%. Some patients with chronic lung disease or sleep apnea can have normal levels around 90%.
A warning for any health care provider is if patient experience shortness of breath or when measured SpO2 is <95%.1
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.2