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Friday, February 23, 2024

The Cold, Hard Work of Delivering Oxygen to Ventilators

Two hospitals in Queens, New York moved 10 Covid-19 patients to a Navy hospital ship docked offshore last week, after their ventilators couldn’t supply as much oxygen as the patients needed. The problem lay not with the hospitals’ total oxygen supply or with the ventilators themselves, but with coils of aluminum in which oxygen changes from a liquid into a gas. And the fix came from the hoses of the New York Fire Department.

As the novel coronavirus attacks the lungs of infected patients, officials worry about the nation’s supply of ventilators, which help the sickest patients breathe. An impromptu cadre of automakers, satellite companies, hobbyists, and others has mobilized to build more ventilators. But those ventilators need a reliable supply of oxygen. So a second network of suppliers and health care workers is racing to shore up a supply chain that’s rarely seen—partly because it’s literally invisible.

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Oxygen is stored and transported as a supercooled liquid—at temperatures below minus-300 degrees Fahrenheit—because it is safer and takes up dramatically less space that way. But it must be converted into a gas to help patients breathe. That happens in the aluminum coils, which form a device known as an ambient air vaporizer. Problems arise when moisture in the air condenses on the surface of the coils and freezes, lowering the temperature of the oxygen gas inside, and disrupting the regulators that control the flow of oxygen to patients.

When a hospital needs to run its vaporizers at full tilt to feed an unprecedented number of ventilators, the vaporizers don’t get a chance to defrost, says Bob Sutter, a bulk gas expert and the head of health care systems at B&R Compliance Associates, who helped troubleshoot the problem in Queens. “They never get a break,” he adds. Sutter gave the New York State Division of Homeland Security and Emergency Services some simple, effective advice: Ask the fire department to defrost the vaporizers by blasting them with water.

The oxygen supply chain begins at more than 2,500 plants in the US and Canada that distill oxygen from air in a process similar to the way gasoline and other products are refined from crude oil. In the case of oil, that’s done with heat, where the liquid crude converts to gases that then condense back to liquids. By contrast, air is cooled to extremely low temperatures where its components—such as nitrogen, argon, and oxygen—become liquids.

On a typical day not during a pandemic, the health care industry consumes 2,600 tons of oxygen, says Rich Gottwald, the president and CEO of the Compressed Gas Association, an industry group. “There is no shortage of medical oxygen,” Gottwald says, “nor do we anticipate any shortage.” That’s partly because companies such as Airgas, Linde, and Air Products have ramped up production and shifted capacity to serve the most hard-hit areas of the country.

Problems are more common at a hospital, with vaporizers or other equipment. The networks of pipes that move the gas through the building can be overwhelmed, especially when demand is high. Some pipes move pure oxygen. Others carry “medical air,” which has been filtered and dried. If the dehumidifiers that remove humidity are overloaded, moisture can get into the air lines and damage ventilators. So far, the movement of oxygen has been the more pressing issue.

The oxygen shortage at the two Queens hospitals is a rarity, even amid the pandemic. Rich Branson, a respiratory therapist at the University of Cincinnati who researches mechanical ventilation in mass casualty situations, says people at several hospitals have told him in the past week of seeing low oxygen pressure alarms in their systems, despite having plenty of liquid oxygen in their tanks. Hospitals usually build their systems to handle 50 percent more oxygen than what they’d consider a high level of demand, Branson reports. But a surge of Covid-19 patients, who tend to need high rates of oxygen for long periods, seems to be pushing them past that point. “You’re trying to draw more gas out of the system through those long pipes faster than it can be delivered,” he says. He compares the problem to taking a shower on the top story of a big apartment building when every other resident is running every faucet at the same time.


That kind of drop isn’t disastrous—ventilators can work with a range of pressures—but could ultimately lead to a failure of the oxygen system. Such a cataclysm is unlikely, Branson notes, but he and a colleague published a document offering some practical ways to avoid pipeline problems. They advise turning off oxygen to manual resuscitators when they’re not in use (the flow is often left on so they’re ready to use at all times), and not giving patients any more oxygen than they need to get their blood levels to normal. “Give the least amount of oxygen you need to give to keep it normal,” Branson says.

Hospital staff have other ways to prevent blockages. Sutter, the consultant who told the New York hospitals to call in the fire department, suggests switching between vaporizers (most places have a couple) more frequently, maybe every six hours instead of 12 hours, to prevent ice buildup. He also recommends deicing the devices before the cold becomes a problem. He’s working with one hospital in California, which he declines to name, that’s hustling to install temporary vaporizers in case of a surge in Covid-19 patients.

Meanwhile, health care workers closer to patients are testing and troubleshooting potential problems. “We had a theoretical, doomsday scenario,” says James Baker, a respiratory therapist at the Mayo Clinic in Minnesota. Workers hooked up a bunch of ventilators in an unused part of the hospital, ran them at the max, and looked for drops in pressure.

Matthew Baretich, head of clinical engineering firm Baretich Engineering, says he’s heard of clinics that added piping to move more oxygen after running similar tests. That required construction at a time when workforces are diminished by the pandemic. “It’s exactly as hard as you’d imagine,” he adds.

When oxygen finally reaches a patient’s bedside, nurses and therapists work to maximize a ventilator’s benefits. “People might just be looking at the machine itself,” says Elizabeth Postovit, who directs the respiratory therapist program at Ohlone College in Fremont, California. But healing a Covid-19 patient takes more than just a machine—it takes a network.

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