NEW YORK (Reuters) - At least one New York hospital has begun putting two patients on a single ventilator machine, an experimental crisis-mode protocol some doctors worry is too risky but others deemed necessary as the coronavirus outbreak strains medical resources.

The coronavirus causes a respiratory illness called COVID-19 that in severe cases can ravage the lungs. It has killed at least 281 people over a few weeks in New York City, which is struggling with one of the largest caseloads in the world at nearly 22,000 confirmed cases.

A tool of last resort that involves threading a tube down a patient’s windpipe, a mechanical ventilator can sustain a person who can no longer breathe unaided. The city only has a few thousand and is trying to find tens of thousands more.

Dr. Craig Smith, surgeon-in-chief at New York-Presbyterian/Columbia University Medical Center in Manhattan, wrote in a newsletter to staff that anesthesiology and intensive care teams had worked “day and night” to get the split-ventilation experiment going.

By Wednesday, he wrote, there were “two patients being carefully managed on one ventilator.”

New York Governor Andrew Cuomo, who says his staff is struggling to find enough machines on the market, has touted the adaptation as a potential life-saver. “It’s not ideal,” he told reporters, “but we believe it’s workable.”

The U.S. Food & Drug Administration, which regulates medical device manufacturers, gave emergency authorization on Tuesday allowing ventilators to be modified using a splitter tube to serve multiple COVID-19 patients, though manufacturers still must share safety information with regulators.

Some medical associations oppose the unproven method.

On Thursday, the Society of Critical Care Medicine, the American Association for Respiratory Care and four other practitioner groups issued a joint statement saying the practice “should not be attempted because it cannot be done safely with current equipment.”

It is difficult enough to fine-tune a ventilator to keep alive even one patient with acute respiratory distress syndrome (ARDS), the statement said; sharing it across multiple patients would worsen outcomes for all. They proposed doctors instead choose the one patient per ventilator deemed most likely to survive.

At Columbia, Smith noted that they could not split a ventilator across just any two COVID-19 patients, but were only pairing patients with sufficiently similar respiratory needs.

Across Manhattan, Mount Sinai Hospital told staff in an email that officials were “working to figure out” whether they could split ventilators. The hospital has ordered the necessary adapters, a nurse there said in an interview on condition of anonymity because she was not authorized to speak to reporters.

Experts at Columbia pointed to a 2006 study where researchers, using lung simulators, concluded that a single ventilator could sustain four adults in an emergency scenario.

One author of that study, Dr. Greg Neyman, cautioned against the application in COVID-19 cases in part because the lungs themselves are infected. If one patient’s lungs were deteriorating faster, he said, it could cause imbalances in the closed system. One patient could starve for oxygen while the other patient’s lungs would get increased pressure.

“Unless they were very very closely monitored, such a set up may end up doing more harm than good,” Neyman wrote in an email to Reuters.