April 7, 2020 -- As doctors treat more patients who are severely ill from COVID-19, they’re noticing differences in how their lungs are damaged.

Some patients coming to the hospital have very low oxygen levels in their blood, but you wouldn’t necessarily know it from talking to them. They don’t seem starved of oxygen. They may be a little confused. But they aren’t struggling to breathe.

When doctors take pictures of their lungs -- either with a CT scanner or an X-ray machine -- those also look fairly healthy. The lungs may have a few areas of cloudiness and crazing, indicating spots of damage from their infection, but most of the lung is black, indicating that it is filled with air.

One doctor treating COVID-19 patients in New York says it was like altitude sickness. It was “as if tens of thousands of my fellow New Yorkers are stuck on a plane at 30,000 feet and the cabin pressure is slowly being let out. These patients are slowly being starved of oxygen,” said Cameron Kyle-Sidell, MD, an emergency room and critical care doctor at Maimonides Medical Center in Brooklyn who has been posting about his experience on social media.

“A whole bunch of these patients really have low oxygen, but their lungs don’t look all that bad,” says Todd Bull, MD, director for the Center of Lungs and Breathing at the University of Colorado School of Medicine, in Aurora.

Doctors in Italy have noticed the same thing. And in some cases, that might mean patients need to be treated a little differently to ensure the best outcome.

In an editorial in the journal Intensive Care Medicine, Luciano Gattinoni, MD, a guest professor of anesthesia and intensive care at the University of Gottingen in Germany, and one of the world’s experts in mechanical ventilation, says more than half the patients he and his colleagues have treated in Northern Italy have had this unusual symptom. They seem to be able to breathe just fine, but their oxygen is very low.