What explains coronavirus's "happy hypoxics"?

Hypotheses about what causes it are emerging. Many doctors now recognize clotting as a major feature of severe COVID-19. Negri thinks subtle clotting might begin early in the lungs, perhaps thanks to an inflammatory reaction in their fine web of blood vessels, which could set off a cascade of proteins that prompts blood to clot and prevents it from getting properly oxygenated.

Negri developed this idea after treating a woman whose breathing troubles coincided with circulatory problems in her toes. Negri’s team gave the woman heparin, a common blood thinner, and not only her toes but her breathing recovered. Negri wondered whether heparin could boost patients’ low oxygen levels regardless of whether they were struggling to breathe. On 20 April, she posted a preprint detailing her hospital’s experience with 27 COVID-19 patients. Patients with hypoxia received heparin, and the dose was increased if they had elevated levels of D-dimer, a blood marker of excess clotting.

One of the 27 was lost to follow-up after transferring to another hospital. But 24 others are recovering—including six of eight who needed mechanical ventilation, a better rate of positive outcomes than has been reported elsewhere.