he Covid-19 pandemic is an unprecedented event in modern medical practice, and health care providers are seeing extraordinary numbers of severely ill people. Many providers think the novel coronavirus is causing the human body to behave in weird ways. In some cases, they may be right — but not in all of them.
Some of the side effects associated with Covid-19 are unusual symptoms for a respiratory infection while others are simply being observed by doctors more often because of the sheer number of people infected. As the pandemic unfolds, both physicians and the public are struggling to differentiate between the two as a way to better understand the virus. Below are three symptoms that have received recent attention.
Easily clotting blood
One symptom that has been described as a mysterious complication of Covid-19 infection is the presence of blood clots in people with more severe forms of the disease.
In a prepublication study recounting the autopsy findings of 20 people in Louisiana who died from Covid-19, the authors described clotting in the small blood vessels of many patients’ lungs. A group of Dutch scientists also described a series of hospitalized people who had clotting complications; most of those complications were in the veins of the lungs.
The process of clot formation in human blood involves hundreds, if not thousands, of proteins and cells. Doctors who specialize in blood diseases can usually identify the cause of a clotting disorder by looking for patterns in blood tests that measure those proteins and cells’ abundance.
But the clotting that accompanies many severe Covid-19 infections evades that effort. Blood tests in people with these infections “don’t fit into the usual patterns,” says Adrienne Phillips, MD, a specialist in hematology and oncology at Weill Cornell Medicine in New York City. This makes it hard to determine the root cause of clotting in these people, which in turn makes it difficult to make broad recommendations for preventing or treating those clots.
Another unusual feature of the clotting associated with Covid-19 is related to the size of the blood vessels where the clots are found. Critically ill people who do not have Covid-19 often develop clots in large blood vessels as a side effect of not moving much and having disease-related inflammation in their bodies. These factors make clotting so likely that for years, most critically ill people have received clot-preventing medication as a matter of course while they’re in the hospital.
But many people with Covid-19 who are on clot-preventing medications are nevertheless developing clots in their lungs — and not just in the large blood vessels but in very small ones, too. “That’s what makes this clotting unique,” says Phillips. The unusual locations of these clots raise the concern that clotting is not just a side effect of a Covid-19 infection but is actually a feature of it.
Because these clots’ characteristics are so unusual, and because of the growing concern that clotting is responsible for much of the havoc the infection wreaks, several studies are underway to investigate whether drugs that prevent or bust clots can help people infected with the novel coronavirus.
While this set of symptoms might feel unusual, it’s really the number of people experiencing it that’s unusual rather than the symptom itself.
The presence of “happy hypoxia,” a phenomenon in which people with low blood oxygen levels do not actually feel short of breath, has also been treated in news reports as a clinical conundrum. Although the spectrum of lung disease that Covid-19 causes is still not completely understood, this particular symptom is nothing new, says Martin Tobin, a professor of pulmonary and critical care medicine at Loyola University.
When it comes to the ways lungs work in the setting of Covid-19 infection, “our understanding of how the body reacts to major challenges remains the same,” he says.
At baseline, human bodies need a steady supply of fresh oxygen to live, and so people constantly produce carbon dioxide waste as a side effect of normal metabolism. Healthy lungs exchange oxygen for carbon dioxide in the lungs’ many tiny air sacs.
When a portion of the lungs has a complete blockage of air or blood flow, that exchange doesn’t happen and oxygen levels drop. But carbon dioxide, which exchanges more readily than oxygen, can still escape the lungs as long as the rest of the lung tissue is relatively healthy and not stiffened by age or disease, like uncontrolled asthma or severe pneumonia.
That results in low oxygen levels and low carbon dioxide levels — and people can actually feel pretty comfortable with low oxygen levels if they are not exerting themselves, says Tobin. Before this pandemic, doctors occasionally saw this same pattern in people with healthy lungs who had developed a bacterial pneumonia called “lobar” pneumonia.