It is a mystery that has prompted doctors to question the basic principles of biology: Covid-19 patients who speak and seemingly not in distress, but have oxygen levels low enough to usually cause loss of consciousness or even death.
The phenomenon, known by some as “happy hypoxia” (some prefer the term “silent”), raises questions about exactly how the virus attacks the lungs and whether there might be more effective ways to treat these patients. .
A healthy person should have an oxygen saturation of at least 95%. But doctors report that patients attend A&E with percentage oxygen levels in the 80s or 70s, with some drastic cases below 50%.
“It is fascinating to see so many people arriving, how hypoxic they are,” said Dr. Jonathan Bannard-Smith, an intensive care and anesthesia consultant at the Manchester Royal Infirmary. “We see very low oxygen saturations and they don’t know it. We wouldn’t usually see this phenomenon in the flu or community-acquired pneumonia. It is much deeper and an example of very abnormal physiology taking place before our eyes. “
Dr Mike Charlesworth, an anesthesiologist at Wythenshawe Hospital in Manchester, said that while other lung conditions could cause severe hypoxia, these patients normally appeared to be extremely ill. “With pneumonia or pulmonary embolism, they would not be sitting in bed talking to you,” he said. “We just don’t understand. We don’t know if it’s causing organ damage that we can’t detect. We don’t understand if the body is compensating.”
Charlesworth had personal experience of the problem while suffering from Covid-19 in March. After feeling bad with a cough and fever, he spent 48 hours in bed, during which there were signs of hypoxia, he said. “I was sending very strange messages on my phone. I was basically delusional. Looking back, I probably should have come to the hospital. I’m pretty sure my oxygen levels were low. My wife said my lips were very dark. But I was probably hypoxic and my brain was probably not working very well. “
He recovered after a few days in bed, but he and others are aware that not all cases have had positive results.
An anesthesiologist from a London hospital, who spoke anonymously, recalled a patient who had consulted A&E saying she was cold. “When we asked him the statistics probe, his saturation was 30% in the air,” he said. “We obviously thought it was wrong, because generally patients are likely to have hypoxic cardiac arrest.” But when a blood sample was taken, his blood was very dark and had oxygen levels equivalent to those seen in people acclimatized at high altitudes. The patient was placed on a ventilator and survived for about a week before dying. “I have had a few patients like this,” said the doctor. “Unfortunately, their results tend to be poor in my experience.”
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Conventional medical wisdom is that as oxygen supplies decrease, the heart, brain and other vital organs are put at risk – and the effect is believed to be cumulative. As a rule, patients lose consciousness under 75% oxygen saturation.
However, it is not the drop in oxygen levels itself that leaves people breathless. Instead, the body detects the increasing levels of carbon dioxide that generally occur simultaneously, as the lungs are unable to purify the gas as effectively. But in some Covid-19 patients, this response does not seem to be triggered.
“I don’t think any of us expect what we see can be explained by a single process,” said Bannard-Smith.
Swelling and inflammation of the lungs will likely make it difficult for oxygen to enter the bloodstream. There is also new evidence that Covid-19 can cause blood clotting. The pulmonary vessels that collect oxygen and transfer it to the larger bloodstream are so tiny that they can become blocked with the smallest clot.
Several clinical trials are looking at whether blood thinners could prevent or treat the complications of Covid-19, including breathing problems and low oxygen levels in the blood.
Some have suggested that, as people are often oblivious to the drop in oxygen levels, people with symptoms of Covid-19 or a positive test result should receive pulse oximeters, a simple device that attaches to the finger and can be used to detect oxygen levels at home. However, so far there is no evidence that early detection of hypoxia would avoid serious outcomes and Charlesworth said the practicalities would be difficult.
“Transporting the aircraft would put more people on the road,” he said. “Then there are problems with the people who buy them on the Internet and [have proper safety certificates] … If you are about to need to monitor your oxygen levels, now is the time to go to the hospital. “
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