If the iconoclasts are right, putting coronavirus patients on ventilators could be of little benefit to many and even harmful to some.

What’s driving this reassessment is a baffling observation about Covid-19: Many patients have blood oxygen levels so low they should be dead. But they’re not gasping for air, their hearts aren’t racing, and their brains show no signs of blinking off from lack of oxygen.

That is making critical care physicians suspect that blood levels of oxygen, which for decades have driven decisions about breathing support for patients with pneumonia and acute respiratory distress, might be misleading them about how to care for those with Covid-19. In particular, more and more are concerned about the use of intubation and mechanical ventilators. They argue that more patients could receive simpler, noninvasive respiratory support, such as the breathing masks used in sleep apnea, at least to start with and maybe for the duration of the illness.