Ordinarily, in patients with healthy lungs, an oxygen-saturation level below 90 per cent is cause for grave concern: when vital organs such as the heart and brain become starved for oxygen, the risk of death skyrockets. But doctors are finding, bizarrely, that some COVID-19 patients can remain subjectively comfortable even when their saturation levels fall far below these ranges. Watch more: http://nyer.cm/Er1lst0 | The New Yorker