除了呼吸机，国外医院又有一关键物资告急

Oxygen supplies have emerged as the latest choke point in the battle against the coronavirus.

Many patients hospitalized with COVID-19 infections, even those not sick enough to be placed on a mechanical ventilator, have impaired lung function and require supplemental oxygen.

The number of these patients—and the amount of oxygen they are requiring—is threatening to exhaust hospitals’ supply, and industrial gas producers are scrambling to keep pace with the demand.

Hospitals normally have large central tanks for the storage of liquid oxygen, which is then evaporated into a gas and piped throughout the facility. Some also use smaller canisters of liquid oxygen.

But in Italy, hospitals have reported their daily consumption of oxygen has more than tripled during the pandemic as the number of patients needing ventilators and other forms of supplemental oxygen has soared. Some hospitals in the north of the country, the region at the epicenter of the outbreak, have been forced to install additional large storage tanks to ensure an adequate supply.

In the U.K., one major London hospital reportedly came close to exhausting its oxygen supply last weekend. This resulted in an urgent letter from the National Health Service instructing doctors to calculate the maximum number of patients they can support on oxygen at any one time, and to limit the use of continuous positive airway pressure (CPAP) machines, which doctors have been using to help patients who are not yet sick enough to require a ventilator.

CPAP machines and other forms of what’s known as “high-flow nasal oxygen,” which deliver oxygen directly into a patient’s nostrils through tubing, often consume far more oxygen per hour than ventilators. Hooking too many patients up to high-flow piped oxygen simultaneously can also create pressure imbalances across the hospital’s oxygen network, leading the entire system to suddenly fail, jeopardizing all the patients in the hospital who are currently receiving wall-based oxygen, the NHS said.

The NHS warning raises the prospect that even if the U.K. is able to produce enough ventilators to meet the demand from coronavirus patients, the available supply of oxygen may ultimately become a limiting factor in the number of patients able to receive lifesaving treatment.

Meanwhile, in New York City, a number of doctors have said their hospitals have also come perilously close to running out of piped oxygen. They have reported running low on oxygen canisters, which some hospitals have begun using to treat patients because all of their piped oxygen connections are already in use.

Biju Mohan, a vice president at GEP, a global supply-chain consulting firm based in Clark, N.J., and a specialist in the pharmaceutical and health care industries, said estimates of the surge in demand for medical oxygen range widely between 25% and 500%. He said most manufacturers operate with about 20% spare capacity during normal times and that they should have the ability to meet the surging hospital requirements, especially as demand from other users, such as the construction and oil and gas industry, has plummeted as the economy has ground to a halt.

Pulled from the air

In theory, there are few limits on the amount of oxygen manufacturers can produce. Most producers take in air from the atmosphere, filter it, and then use a cryogenic process, in which the air is cooled to extreme temperatures by an air compressor to separate it into its constituent gases, such as oxygen and nitrogen. These are then further purified and distilled into a liquid or bottled in pressurized cylinders and small canisters. Most of the process is driven by basic physics and heat, with few chemical supplies involved.

The bigger practical problem, Mohan said, is that hospitals normally receive oxygen in liquid form, which is then evaporated into gas and piped throughout the hospital. Hospitals have limited storage capacity for liquid oxygen, and delivery fleets are having to make many more trips than normal to keep these tanks filled, he says.

Ganesh Suntharalingam, a doctor who is president of the U.K.’s Intensive Care Society, said during an online seminar sponsored by the Association of Anaesthetists earlier this month, that most hospitals’ oxygen tanks have sensors that automatically order more supply when tank levels drop to a certain threshold. But with the rate of oxygen depletion much higher than normal—and high demand from so many hospitals occurring at the same time—“for that hospital to not run out that day is going to be a challenge.”

In some cases, he said, hospitals could find their oxygen supplies completely depleted “within hours rather than days.”

Mohan said that it should be possible for hospitals to supplement their piped oxygen supplies with large cylinders of oxygen, which are normally used for industrial customers, but that there are regulatory obstacles to doing so—these cylinders are not licensed for use in medical settings. Air Liquide, one of the world’s largest medical gas suppliers, has said it is considering asking for regulatory approval to do this.

In the U.K., the government has asked BOC, an oxygen producer and official supplier to the National Health Service, to quadruple production to meet the anticipated demand as coronavirus cases peak in the coming weeks. “BOC is working closely with government departments within the U.K. to develop processes and procedures to cope with an increased demand of medical gases associated with the current COVID-19 outbreak,” the company, which is a subsidiary of Linde, one of the world’s largest industrial gas producers, said in a statement.

BOC has been building up stocks of medical gases in preparation for the pandemic, the company said, and has also increased its fleet of tankers for trucking gas to hospitals. The British military has been placed on standby to help drive oxygen tankers if BOC’s own drivers start to fall ill or have to self-isolate.

BOC and Air Liquide have both asked medical customers who use oxygen gas in canisters to return empty ones promptly so they can be refilled and sent out again.

Air Products, another major industrial gases producer headquartered in Allentown, Pa., said in a statement that it is “not currently experiencing any production shortages” owing to the pandemic and that it “continues to review and evaluate its entire robust supply chain, redundant backup plans, and network of facilities to meet customers’ demands.

“This is a dynamic and fluid situation, which makes it difficult to predict its future impact or exact duration,” the company said.