Silent hypoxia is when pulse oximetry checks on a patient who does not appear to be short of breath, which results in oximetry finding lower than a physical would expect.
This occurred in a number of situations, but most recently it has made headlines because of the large number of incidences of this occurring in individuals who are diagnosed with COVID-19.
Why Is Hypoxia Thought To Occur In Some Of The COVID-19 patients? Why Is It Occurring As Silent Hypoxia?
As with lots of things regarding COVID-19, we are going to rely on more data and studies that show how many individuals develop the sign of silent hypoxia. There are probably many COVID-19 patients with hypoxemia who get missed because they are admitted and diagnosed with many other symptoms such as fever, cough, or other symptoms like this.
I think we are going to need to look at a large group of people to figure out why exactly the virus causes silent hypoxia, compared to other viruses like influenza where it is not seen as often.
There is something different new about this virus in the way that it affects the blood vessels and the airways. There are even some ideas that the virus is affecting the nervous system and affecting the actual mechanism in our brain which helps in regulating respiration.
The mechanism of why oxygen levels drop has to do with, how well the blood flows through the lungs that match the airflow through the lungs. For some reason, which we cannot identify in certain patients the virus affects the blood vessels in the lungs as well as air sacs in the lungs, mismatching the flow of blood and air that cause the oxygen levels to drop.
The reason that individuals are not feeling as short of breath or appear to be short of breath is still a bit of mystery. As with a lot of things to do with COVID-19, this has not been determined till now.
Perhaps the virus is affecting the blood vessels lack ability to constrict the way they are supposed to, or perhaps there is actually some central effect on the brain where the respiratory effort is not picked up because the virus is affecting the brain’s ability to identify the hypoxia.
It may be that the oxygen level is dropping without changing in the way of the lung mechanics, meaning that the lung is not becoming stiffer and the patient does not feel any distress when they are breathing in and out, because there is no increase in breathing work.
The lungs may not be sensing that the oxygen level is dropping, but the concern is that the other organ in the body is not getting as much oxygen as required.
There are a lot of theories right now as to why this virus is acting differently, but answers are identified yet. We cannot identify how many people or which individuals are going to develop silent hypoxia at the moment.
What Leads To Silent Hypoxia In COVID Patients?
COVID-19 triggered pneumonia causes oxygen deprivation that is difficult to detect since the patients do not feel any noticeable difficulties in breathing. Patients with Covid may be suffering from this despite any signs of breathlessness and may be seriously ill without being aware of the condition like hypoxia.
Usually, a low level of oxygen is accompanied by an unpleasant subjective sensation of breathlessness felt by the patient. However, breathlessness is a complicated symptom and is affected by lots of factors apart from blood oxygen levels. If the lungs become stiff or fluid-filled, the muscle must work harder to ventilate the lungs. This also contributes to the sensation of shortness of breath.
Usually, in pneumonia, the lungs become filled with fluid. In contrast, in patients with COVID-19, there is little fluid in the lungs, in the early stages of illness. This is because COVID-19 uniquely attaches to a protein called ‘ACE2’ that is present in the blood vessels. When blood passes through the vessels in the lungs, it takes oxygen from the air. This oxygen-rich blood is then transported across the whole body. It is now understood that COVID-19 may affect blood vessels of the lungs thereby impairing oxygen delivery to the body. Hence, in COVID-19 there may be a low amount of blood oxygen levels. This triggers the patient to breathe deeply however the lungs are not fluid-filled or stiff, the patient may not experience any breathlessness that the disease becomes more advanced.