The reason: Some hospitals have reported unusually high death rates for coronavirus patients on ventilators, and some doctors worry that the machines could be harming certain patients.

The evolving treatments highlight the fact that doctors are still learning the best way to manage a virus that emerged only months ago. They are relying on anecdotal, real-time data amid a crush of patients and shortages of basic supplies.

Mechanical ventilators push oxygen into patients whose lungs are failing. Using the machines involves sedating a patient and sticking a tube into the throat. Deaths in such sick patients are common, no matter the reason they need the breathing help.

Generally speaking, 40% to 50% of patients with severe respiratory distress die while on ventilators, experts say. But 80% or more of coronavirus patients placed on the machines in New York City have died, state and city officials say.