Why Oxygen levels in Covid reduce?

The Covid spread in India is reaching dangerous heights- but more than that is the increase in videos and WhatsApp forwards that try to tell you how you can manage oxygen in Covid.

In normal circumstances, it has been observed that 98% of people suffering from Covid will recover. And out of this 98% only a meagre of 0.01% require ICUs or reach stage of critical illness. One of the major causes of death during covid infection is silent-Hypoxia- or in other words low oxygen level- this can damage the vital organs in the body- if gone undetected- or untreated.

The Oxygen level is maintained by lungs. Healthy lungs maintain the blood oxygen level between 95 and 100 percent -- if it gets below 92 percent, it's a cause for concern and doctor intervention might be needed.

In the initial months, it was presumed that since lungs get infected, that is the reason for low oxygen level in Covid patients. However, Boston University researchers, found that oxygen level was excessively low even in patients whose lungs showed little to no sign of any abnormality in lung scans. This made them question the theory- and eventually they found three reasons contributing to the low level of oxygen in human body under Covid infection:

1. Normally, the lungs have the ability to constrict blood flow to the areas of the lung that are infected or damaged. But in Covid this ability is lost and blood goes even to the damaged tissues. Nitric Oxide (NO) has been reported to improve blood flow in the areas of the lung that are getting air. And there are clinical trials- which are trying to investigate if NO can be helpful in treating Covid. And probably NO based nebulisers maybe useful.
2. The second reason is the presence of tiny blood clots in the lungs. The reason why blood clots are formed- is under investigation, and will tell you about it in other post. For now, it is sufficient to know that these tiny clots in the lungs reduce the oxygen capacity. To avoid clot formation- doctors have suggested anti-coagulants in the treatment of Covid.
3. And lastly Covid changes the ratio of air-to-blood flow in the lungs. For oxygen to transfer to the blood the ideal V/Q ration should be one. Here the V refers to ventilation-the air that reaches the alveoli in lungs, and Q refer to the perfusion- the blood the alveoli via blood capillaries. Covid results in V/Q mismatch. It has been observed that Prone position reduces the V/Q mismatch to some extent. Thus lying chest down and back up will be helpful to some extent.

Kindly note that in case oxygen level of the person goes below 92% immediately seek medical help. The aim of this article is to help you understand why Oxygen level goes down- and why just any Nebulizer or Steam inhaling or Steroids are not going to work - if the patient is in that unfortunate 2% slot.

Take care, stay safe, stay informed.

References

1. Jacob Herrmann, Vitor Mori, Jason H. T. Bates, Béla Suki. Modeling lung perfusion abnormalities to explain early COVID-19 hypoxemia. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-18672-6
2. Boston University. "Three reasons why COVID-19 can cause silent hypoxia: Biomedical engineers use computer modeling to investigate low blood oxygen in COVID-19 patients." ScienceDaily. ScienceDaily, 19 November 2020.
3. Worldometers.info, Dover, Delaware, USA.
4. Mure M, Domino KB, Lindahl SGE et al (2000) Regional ventilation-perfusion distri-bution is more uniform in the prone position. J Appl Physiol 88:1076-1083