Gunshot victims with massive blood loss and failing lungs packed the emergency room of Sunrise Hospital in Las Vegas late on the night of Oct. 1, 2017. A man had opened fire on a music festival from the 32nd floor of the Mandalay Bay Hotel, spraying more than a thousand rounds of ammunition into the crowd, wounding hundreds.

The hospital soon ran out of ventilators, machines that breathe for patients who can’t. Dr. Kevin Menes, a critical care physician, had several patients in respiratory failure. Menes remembered that a colleague from his medical residency had studied how to connect multiple people to a single ventilator. When a respiratory therapist said to Menes, “‘We don’t have any more ventilators,’ I said, ‘It’s fine,’” he later recalled. He asked for tubing and began splitting one machine’s oxygen flow into two patients, saving their lives.

Now, Menes’ makeshift strategy may well be adopted by desperate caregivers worldwide. As hospitals anticipate more COVID-19 patients with respiratory failure to arrive than they have ventilators to hook them to, the idea of using one ventilator for two or more patients has gained widespread attention and support, including at two prominent Manhattan hospitals.

But interviews with critical care workers and a review of the medical literature show that plugging more than one person into the same ventilator is a stopgap that risks harming patients’ lungs. At best, many doctors say, it’s a last resort for patients who have stopped breathing on their own and have no other prospect of surviving.

A ventilator is designed and can be set for only one patient at a time. Since two patients are unlikely to require oxygen at the same amount and pressure, one might get too little oxygen while the other receives too much, injuring their lungs either way. Also, the air tubes might distribute contaminants between patients. Reflecting these concerns, one major ventilator manufacturer and the American Association for Respiratory Care both discourage hospitals from connecting machines to multiple patients. Some hospitals are reluctant to try it under any circumstances and are looking for other backup plans.

“This is not a panacea,” said Dr. Lewis Rubinson, chief medical officer at Morristown Medical Center in New Jersey and a longtime critical care physician. “We don’t want a solution that’s a distraction, and that’s what this has become.”

Some see it not as a distraction but as a lifesaver at a time when the U.S. health care system has about 160,000 ventilators available, less than half of the number most statistical models estimate it will need to treat gravely ill coronavirus patients. A YouTube video posted by a critical care doctor in Detroit, demonstrating how to connect up to four patients to one ventilator, has been viewed more than 800,000 times in the past 10 days. A physician at a rural hospital in Canada told reporters he has doubled the number of patients he can ventilate at one time by following the video’s directions.

In New York City, which has almost 30% of the nation’s coronavirus cases, intensive care units at NewYork-Presbyterian Hospital and the Columbia University Irving Medical Center are testing how to use “split-ventilation,” Dr. Craig Smith, the hospitals’ chief surgeon, said in a note to staff this week. Smith lauded plans to care for multiple patients with one ventilator as a critical innovation, and he wrote, “Today a technique forged in the crucible of mass trauma is helping our medical colleagues manage COVID-19.”

New York Gov. Andrew Cuomo on Tuesday endorsed its use. “We are going so far as to try an experimental procedure where we split the ventilators,” he said. “We use one ventilator for two patients. It’s difficult to perform, it’s experimental, but at this point we have no alternatives.”

Some hospitals are already on the brink of running out of ventilators. A critical care physician in New Jersey, who asked not to identify herself or her employer, said the facility was treating dozens of patients who had tested positive for COVID-19, while several dozen others awaited test results. A young patient arrived, struggling to breathe, and “suddenly there was panic around where we were going to get the next ventilator from,” the doctor said. Eventually, a ventilator was found for the child.

A ventilator pumps oxygen into a patient’s airways when the lungs are too injured or sick to breathe on their own. Typically, for COVID-19 patients, physicians and respiratory therapists first run tubes into the airway to deliver oxygen to the lungs. Then they set how often the machine breathes for the patient and how much oxygen it sends. Using sensors, the ventilator tracks everything about the breaths — their length, the amount of resistance the air hits in the body and how much the lungs expand and contract. Medical staff use the information to determine whether the treatment is working and to make adjustments.

With multiple patients connected, a ventilator becomes a blunt instrument. The tubes are adjusted so the air the ventilator pumps out is divided between two or four tubes, each going into a different set of lungs. It moves air in and out of each person, or at least tries to. Doctors and therapists must choose carefully which patients to pair, matching them by gender, body size and diagnosis.

This is highly inexact, Rubinson said. Sicker patients, whose lungs resist more, take in less of the oxygen. Stronger patients take in more air, which can cause its own problems. The machine cannot adjust, and it is difficult for the critical care staff to do so either.

Early studies of whether ventilators could work on more than one patient involved testing them on artificial lungs that simulate the function of actual lungs. In 2006, a pair of emergency doctors at St. John’s Hospital and Medical Center in Detroit, anticipating “a large outbreak of botulism” or other disaster for which hospitals would not have enough ventilators to go around, found that a ventilator could inflate and deflate multiple artificial lungs, but could not address whether there would be adequate oxygen or any potential for lung injuries. A follow-up study on animals found that ventilators struggled to distribute air evenly. There has never been a controlled test on human subjects.

The flaws are well understood on most intensive care units. Even hospitals including the technique in emergency plans for COVID-19 plan to use it only as a last resort. “In a short term scenario, it would be a potentially lifesaving choice” when a hospital has run out of ventilators, said Dr. Gregory Martin, head of critical care at Grady Memorial Hospital in Atlanta.

However, “there isn’t a way to necessarily decide how much oxygen, or how much carbon dioxide removal, or what size breath to give” to multiple patients on one ventilator, Martin continued, adding, “We wouldn’t use this solution if we had really any other options.”

At the University of California-San Francisco, the intensive care units are working on ways to cope with a shortage and avoid using the multiple patient technique, said Dr. J. Matthew Aldrich, the system’s executive director of critical care. It is unproven and “I’m not aware of any successful use in this kind of situation.”

Anesthesia machines in operating rooms have ventilators built in, which could at times be used to treat ICU patients, Aldrich said.

The American Association for Respiratory Care, which represents more than 40,000 respiratory therapists, discourages hospitals from connecting two or more patients to a single ventilator, said Tim Myers, an executive at the association. The technique does not allow caregivers to ensure patients are receiving the right amount of air, or to track their respiration.

“How will we know that your lungs are getting better?” Myers said.

Hamilton Medical AG, one of the largest ventilator manufacturers, warns against the multiple patient technique. “Ventilators use sensors to adapt ventilation to every individual patient. This is important with critically ill patients — like COVID-19 patients,” a spokeswoman for Hamilton Medical said in a written response to questions. “If there were several patients on one ventilator, to whom should the ventilator adapt?”

When one patient’s lungs resist the airflow, it travels to the other patients, who then receive more than their lungs need and potentially more than they can tolerate, said Audrey Mak, a retired respiratory therapist in south Texas.

“Say you have a balloon and you’re blowing it all the way, the balloon is going to get weak,” Mak said. “You can do the same thing with lungs.”

Update, April 10, 2020: New York City hospitals have cut back on using the same ventilator for multiple patients because the experimental practice appeared to endanger patients, The New York Times reported.

Maya Miller contributed reporting

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