Doctors fighting coronavirus face a ventilator Catch-22

As critically ill patients struggle to breathe, healthcare workers have deployed invasive ventilators that take on the job for them—and help protect those around them from infection. Critically ill Covid-19 patients usually display symptoms of acute respiratory distress syndrome (ARDS)—they can’t efficiently transfer oxygen from damaged lung tissue to their blood. Typically, the first line of treatment for ARDS is a non-invasive form of assisted breathing: Doctors try to raise oxygen levels by delivering it through a nasal tube, a face mask, or helmet.