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It’s a mystery that has left doctors questioning the basic tenets of biology: Covid-19 patients who speak and are apparently not distressed, but who have oxygen levels low enough to cause unconsciousness or even death.
The phenomenon, known to some as “happy hypoxia” (some prefer the term “silent”) raises questions about how exactly the virus attacks the lungs and whether there could be more effective ways to treat these patients.
A healthy person would be expected to have an oxygen saturation of at least 95%. But doctors report that patients who attend E&E have oxygen percentage levels in the 80s or 70s, with some drastic cases below 50%.
“It is intriguing to see so many people walking in, how hypoxic they are,” said Dr. Jonathan Bannard-Smith, consultant in critical care and anesthesia at Manchester Royal Infirmary. “We are seeing oxygen saturations that are very low and they don’t know it. Generally, we would not see this phenomenon in influenza or community-acquired pneumonia. It is much more profound and an example of very abnormal physiology that presents itself to our eyes. “
Dr. Mike Charlesworth, an anesthetist at Wythenshawe Hospital in Manchester, said that while other lung conditions could cause severe hypoxia, these patients would normally appear extremely ill. “With pneumonia or a pulmonary embolism they would not be sitting on the bed talking to you,” he said. “We just don’t understand it. 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 a 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 that he was hypoxic, he said. “I was sending very strange messages on my phone. He was essentially delusional. Looking back, you probably should have come to the hospital. I’m pretty sure my oxygen levels were low. My wife commented that my lips were very dark. But it was probably hypoxic and my brain probably didn’t work very well. “
He recovered after a few days in bed, but he and others are aware that not all cases have positive results.
An anesthetist at a London hospital, who spoke anonymously, recalled a patient who attended A&E saying he was cold. “When we put the statistics probe on him, his saturation was 30% in the air,” he said. “Obviously we thought that was wrong, since patients generally 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 approximately one week before dying. “I’ve had a few patients like this,” said the doctor. “Unfortunately, their results tend to be bad in my experience.”
Conventional medical wisdom is that as oxygen supplies drop, the heart, brain, and other vital organs are at risk, and the effect is believed to be cumulative. Typically, patients would lose consciousness below 75% oxygen saturation.
However, it is not the drop in oxygen levels that makes people feel breathless. Instead, the body detects the increasing levels of carbon dioxide that generally occur simultaneously, since the lungs cannot eliminate gas as efficiently. But in some Covid-19 patients, this response doesn’t seem to be working.
“I don’t think any of us expect that what we’re seeing can be explained by a process,” said Bannard-Smith.
Swelling and inflammation in the lungs are likely to make it difficult for oxygen to enter the bloodstream. There is also emerging evidence that Covid-19 can cause blood clotting. The vessels in the lungs that collect oxygen and transfer it to the broader bloodstream are so small that they can become blocked by the smallest clots.
Several clinical trials are looking at whether blood thinners could prevent or treat Covid-19 complications, including respiratory problems and low blood oxygen levels.
Some have suggested that since people are often oblivious to decreased oxygen levels, those with Covid-19 symptoms 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 helps avoid severe results, and Charlesworth said the practicalities would be difficult.
“Transporting the devices would put more people on the road,” he said. “Then there are problems around the people who buy them on the Internet and if [have proper safety certificates] … If you are about to need to have your oxygen levels checked, it is time to go to the hospital. “
