The Society of Critical Care Medicine has projected that 960,000 coronavirus patients in the U.S. may need to be put on ventilators at one point or another during the outbreak. But the nation has only about 200,000 of the machines, by the organization’s estimate, and around half are older models that may not be ideal for the most critically ill patients. Also, many ventilators are already being used by other patients with severe, non-coronavirus ailments.