Another threat from the lung virus that causes Covid-19 has emerged that may cause swift, sometimes fatal damage: blood clots.
Doctors around the world are noting a raft of clotting-related disorders -- from benign skin lesions on the feet sometimes called "Covid toe" to life-threatening strokes and blood-vessel blockages. Ominously, if dangerous clots go untreated, they may manifest days to months after respiratory symptoms have resolved.
The clotting phenomenon is "probably the most important thing that's emerged over the last perhaps month or two," said Mitchell Levy, chief of pulmonary critical care and sleep medicine at the Warren Albert School of Medicine at Brown University in Providence, Rhode Island.
It's not unusual for infections to raise the risk of clotting. The 1918 Spanish flu pandemic, caused by a novel strain of influenza that killed some 50 million people worldwide, was also linked to downstream damage from clots that could end lives dramatically.
Viruses including HIV, dengue and Ebola are all known to make blood cells prone to clumping. The pro-clotting effect may be even more pronounced in patients with the coronavirus.
"There's something about this virus that's exaggerated that to the nth degree," said Levy, who is also medical director of the medical intensive care unit at Rhode Island Hospital. "We're seeing clotting in a way in this illness that we have not seen in the past."
The problem is visible in clots -- doctors call them thrombi -- that form in patients' arterial catheters and filters used to support failing kidneys. More pernicious are the clots that impede blood flow in the lungs, causing difficulty breathing.
Rapid Deterioration
These are probably what's causing patients who otherwise appear well to suddenly "fall off the ledge" and develop severe blood-oxygen deficiency, said Margaret Pisani, an associate professor of medicine at the Yale University School of Medicine in New Haven, Connecticut.
Clotting disorders in Covid-19 patients were noted by researchers in China in February, but their gravity has since become clearer. While doctors had thought the vast majority of lung damage was due to viral pneumonia, they're now looking more closely at clotting.
"When you look at autopsies now, we are seeing things that we didn't expect," said Anthony Fauci, the director of the National Institutes of Allergy and Infectious Diseases who's at the forefront of the U.S. pandemic response. Clumps of platelets inside blood vessels, or microthrombi, are probably why Covid patients can "rapidly and dramatically deteriorate," he said in an interview with CNN last week.
Separate studies from France and the Netherlands found that as many as 30% of severely ill Covid-19 patients suffered a so-called pulmonary embolism -- a potentially deadly blockage in one of the arteries of the lungs. These often occur when bits of blood clots from veins deep in the legs travel to the lungs. By comparison, the prevalence of pulmonary embolism was 1.3% in critically ill patients without Covid-19, one study found.
In Italy, the first European country gripped by the pandemic, it was after Covid-19 patients died from acute pulmonary emboli and other clotting-related events that doctors moved to inflammation-blocking treatments, such as tocilizumab, sold by Roche Holding AG as Actemra, said Frank Rasulo, a head of neuro critical care at Spedali Civili University Hospital in Brescia.
Some doctors are starting to see Covid as less of a typical respiratory disease, and more of one that involves dangerous clotting, said Rasulo, who is also an associate professor of anesthesia and intensive care. "That's quite frightening when you think of it, because we didn't know what we're up against until we were in a later stage."
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