In modern day medical sciences, knowing the oxygen saturation of a person’s blood is as easy as feeling for the patients pulse if you are in possession of a pulse oximeter. This device makes use of pulse oximetry which is a technology that was first introduced in 1974 and had since then progressed into a relatively reliable measure of the oxygen saturation in arterial blood.
What is pulse oximetry?
The technology used in modern day pulse oximeters is ‘pulse oximetry’. Although the first ever device used to assess the oxygen saturation was invented in 1930s, it took many decades as mentioned before for the modern day oxygen saturation measuring method to announce its existence.
In this technology, the device makes use of a light with the same wave length as red light and an invisible infrared light of a different wave length to measure the oxygen saturation of hemoglobin molecules. These lights will be emanated using a probe and will be applied to a thin section of the body such as the fingers, ear lobes or else to the foot in small infants. A sensor known as a photodetector is present on the opposite side which will be able to measure the light of both wave lengths reaching the detector through various tissue structures such as venous blood, blood vessels, muscles, skin, bones…etc. Although the measure can be disrupted by the presence of low oxygen saturated venous blood, the pulse oximeter will be able to detect the changing absorption with each pulse and therefore would be arriving at a relatively accurate measure regarding the arterial blood oxygen saturation, which is a representation of the number of oxygen molecules bound by one hemoglobin molecule, in an ideal environment.
What is the ideal circumstance for a pulse oximetry to become accurate?
There are several factors in which the reading from the pulse oximeter can become misleading and among them poor pulsations felt at the application site is a significant contributor. Thus, when a person is having cold hands and the heart does not beat at a regular and an adequate manner to be felt as a relatively prominent pulse, the reading seen in the oximeter may not be reliable.
At the same time, when the probe is not applied correctly and when the skin is too thick for the light to pass through, the measures may become unreliable. At the same time, when the patient is shivering too much or else at a time of having a fit, the readings may not be accurate at all.
In instances of carbon monoxide poisoning and cyanide poisoning the initial readings from the pulse oximeter may delay the detection of oxygen depletion and if the person is on oxygen therapy, the reading would not be indicating the actual oxygen saturation of the patient but will be measuring the result of the ongoing oxygen therapy.
Therefore, interpretation of pulse oximetry should be done by health care professionals who are trained in the said interpretation and it should be understood that, this is not a replacement for measuring arterial blood gases in order to detect respiratory function.
