It is a mystery that has left doctors questioning the basic tenets of biology: Covid-19 patients who are talking and apparently not in distress, but who have oxygen levels low enough to typically cause unconsciousness or even death.
The phenomenon, known by some as “happy hypoxia” (some prefer the term “silent”) is raising questions about exactly how the virus attacks the lungs and whether there could be more effective ways of treating such patients.
A healthy person would be expected to have an oxygen saturation of at least 95%. But doctors are reporting patients attending A&E with oxygen percentage levels in the 80s or 70s, with some drastic cases below 50%.
“It’s intriguing to see so many people coming in, quite how hypoxic they are,” said Dr Jonathan Bannard-Smith, a consultant in critical care and anaesthesia at Manchester Royal Infirmary. “We’re seeing oxygen saturations that are very low and they’re unaware of that. We wouldn’t usually see this phenomenon in influenza or community-acquired pneumonia. It’s very much more profound and an example of very abnormal physiology going on before our eyes.”
Conventional medical wisdom is that as oxygen supplies fall, the heart, brain and other vital organs are placed at risk – and the effect is thought to be cumulative. Typically patients would lose consciousness below an oxygen saturation of 75%.
However, it is not the fall in oxygen levels itself that leaves people feeling breathless. Instead, the body senses the rising levels of carbon dioxide that typically occur simultaneously as the lungs are unable to clear gas as efficiently. But in some Covid-19 patients, this response does not appear to be kicking in.
“I don’t think any of us expect that what we’re seeing can be explained by one process,” said Bannard-Smith.
Swelling and inflammation in the lungs is 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 into the wider bloodstream are so tiny they can become blocked with the smallest of clots.
Read more via The Guardian
