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Silent hypoxia is killing COVID-19 patients.

Mohamed Ibrahim Bassyouni
2020 / 4 / 27




As doctors see more and more COVID-19 patients, they are noticing an odd trend: Patients whose blood oxygen saturation levels are exceedingly low but who are hardly gasping for breath.

These patients are quite sick, but their disease does not present like typical acute respiratory distress syndrome (ARDS), a type of lung failure known from the 2003 outbreak of the SARS coronavirus and other respiratory diseases. Their lungs are clearly not effectively oxygenating the blood, but these patients are alert and feeling relatively well, even as doctors debate whether to intubate them by placing a breathing tube down the throat.
The concern with this presentation, called "silent hypoxia," is that patients are showing up to the hospital in worse health than they realize. But there might be a way to prevent that. If sick patients were given oxygen-monitoring devices called pulse oximeters to monitor their symptoms at home, they might be able to seek medical treatment sooner, and ultimately avoid the most invasive treatments.

This is not a new phenomenon. There are other conditions in which patients are extremely low on oxygen but don t feel any sense of suffocation´-or-lack of air. For example, some congenital heart defects cause circulation to bypass the lungs, meaning the blood is poorly oxygenated.

However, the increased understanding that people with COVID-19 may show up with these atypical coronavirus symptoms is changing the way doctors treat them. Normal blood-oxygen levels are around 97%, Moss said, and it becomes worrisome when the numbers below 90%. At levels below 90%, the brain may not get sufficient oxygen, and patients might start experiencing confusion, lethargy´-or-other mental disruptions. As levels into the low 80s´-or-below, the danger of damage to vital organs rises.

However, patients may not feel in as -dir-e straits as they are. A lot of coronavirus patients show up at the hospital with oxygen saturations in the low 80s but look fairly comfortable and alert. They might be slightly short of breath, but not in proportion to the lack of oxygen they re receiving. 

There are three major reasons people feel a sense of dyspnea,´-or-labored breathing, Moss said. One is something obstructing the airway, which is not an issue in COVID-19. Another is when carbon dioxide builds up in the blood. A good example of that phenomenon is during exercise: Increased metabolism means more carbon dioxide production, leading to heavy breathing to exhale all that CO2.

A third phenomenon, particularly important in respiratory disease, is decreased lung compliance. Lung compliance refers to the ease with which the lungs move in and out with each breath. In pneumonia and in ARDS, fluids in the lungs fill microscopic air sacs called alveoli, where oxygen from the air diffuses into the blood. As the lungs fill with fluid, they become more taut and stiffer, and the person s chest and abdominal muscles must work harder to expand and contract the lungs in order to breathe. 

This happens in severe COVID-19, too. But in some patients, the fluid buildup is not enough to make the lungs particularly stiff. Their oxygen levels may be low for an unknown reason that doesn t involve fluid buildup — and one that doesn t trigger the body s need to gasp for breath.




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