What is silent hypoxia? What you should know about a dangerous effect of the coronavirus

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Silent hypoxia: a hidden killer 2:15

(CNN) - Some have nicknamed them "happy hypoxic." It's a pretty inappropriate name for what could be a long, slow recovery, or even worse.

These are patients who have "silent hypoxia", a dangerous effect of the coronavirus that does not make you short of breath.

This is what you should know:

What is hypoxia?

Hypoxia is a term to describe the lack of oxygen in the blood.

"It means the presence of a lower than normal oxygen level in the blood," explains the Mayo Clinic.

Normal blood oxygen saturation ranges from 95% to 100%, and any level below 90% is considered abnormal.

"When we breathe, air carries oxygen from the atmosphere to our lungs, and oxygen enters the blood in the lungs and carbon dioxide, the famous gas exchange, comes out. Oxygen is vital for humans and there is a brain mechanism that controls the level of oxygen, which is called saturation. It goes between 95 and 96, by the way, it never reaches 100 ″, explains Dr. Elmer Huerta, an oncologist and public health specialist, and CNN en Español collaborator.

The doctor says that if due to a disease or condition or because there is not enough oxygen in the environment, it will not reach the blood and saturation may drop.

"When your brain realizes that your red blood cells do not have oxygen, it triggers the alarm and the person drowns, they are restless because they do not have oxygen," adds Huerta.

So, are there those who have no symptoms?

Exactly. Huerta says he does not have an adequate explanation yet. There are a few cases of patients with coronavirus, explains Huerta, who have saturation of 85 or 84 percent "and are checking their cell phone, they do not realize that their body is in hypoxia."

"It is thought to be brain damage, as if the sensor had failed and does not detect the level of hypoxia. Another theory says that red blood cells are not carrying oxygen, "he adds.

Dr. Richard Levitan, who has been an emergency physician for about 30 years, recently spent nearly two weeks volunteering in the emergency room of a New York City hospital, near the epicenter of the city's devastating outbreak.

There, he observed patients enter the emergency room with very low blood oxygen levels, up to 50%, which should have caused them to be inconsistent, even unconscious.

Who can it happen to?

Huerta explains that it happens to 5% of coronavirus cases and occurs in the second week of the disease.

These patients have generally experienced some symptoms of covid-19 2-7 days before going to the hospital, with complaints of sudden chest tightness or inability to breathe deeply, Dr. Levitan said.

Why is it dangerous?

Levitán said that the tomography scans of these patients revealed signs of pneumonia so severe that they should be in terrible pain as they seek to breathe.

"Their X-rays looked horrible, their oxygenation was terrible, and yet they are wide awake, alert on a cell phone, and they all said they had been somewhat ill for days," he said.

"And then only recently did they notice shortness of breath or fatigue or something else," Levitan added. "That is what is so fascinating about this disease, and also so terrible."

It is horrible because when a person realizes that they are having trouble breathing deeply and decides to seek help, they are already dangerously ill.

"Some may ultimately require an artificial respirator," Levitan noted. "As carbon dioxide levels rise, fluid builds up in the alveoli and the lungs become stiff, leading to acute respiratory failure."

People may not be aware that their breathing rate is going faster and may not seek help, but blood oxygen levels continue to drop. Meanwhile, the body adjusts slowly to the reduction in oxygen, much like what happens when a person travels to a higher altitude than they are used to.

By the time these patients arrive at the hospital with impaired lungs and very low oxygen levels, "this has been going on for a while," said Rutland. "So your body is somehow used to it," he explained.

However, the damage has already occurred. Not only are the lungs severely devastated, but also a lack of oxygen may have compromised other organs in the body, such as the heart, kidneys, and brain.

Silent hypoxia that rapidly progresses to respiratory failure may explain why some young covid-19 patients, without any pre-existing health conditions, have died suddenly after experiencing no serious respiratory distress.