Unless there is direct evidence of hypoxemia, giving oxygen to a person with a suspected heart attack does not appear to be necessary, according to a large open-label test of the therapy conducted at 35 centers in Sweden.

“An established therapy, a mantra almost, that has been used routinely for a century all over the world is without benefit,” the leader of the team, Dr. Robin Hofmann of the Karolinska Institute in Stockholm, told Reuters Health by email.

Although 5.1 percent of patients who received ambient air had died from any cause within a year of their suspected heart attack, the rate was virtually identical, 5.0 percent, among patients who got oxygen for a median of 11.6 hours. The odds of rehospitalization for a heart attack in that one-year period were also comparable: 3.8 percent with oxygen therapy and 3.3 percent with ambient air (P=0.33).

“These results clearly support the view that supplemental oxygen offers no benefit in patients with acute myocardial infarction who have normal oxygen saturation,” said Dr. Joseph Loscalzo of Boston’s Brigham and Women’s Hospital in an online editorial in the New England Journal of Medicine, which released the study online August 28. “It is clearly time for clinical practice to change to reflect this definitive evidence,” Dr. Loscalzo said.

Dr. Hofmann predicted that if guidelines are updated to reflect the new data, it should save time and money. “Paramedics or healthcare staff meeting these patients can now focus on other therapies that the patient benefits from, and try to transport the individual to the nearest hospital with PCI capacity. Remember: time is muscle,” he said.

In addition, although “oxygen is not an expensive therapy, it does cost—and consider the numbers of patients with suspected AMI in the U.S. per year!” he wrote. “In North America, the costs have previously been estimated to $100 per day per patient. This money can be used more efficiently for the patient.”

Registry data served as the basis for the findings in the study, reported Monday at the European Society of Cardiology Congress in Barcelona, Spain.

All 6,629 patients had to have an oxygen saturation of 90 percent or higher to be eligible. Oxygen was delivered through an open face mask at 6 liters per minute for 6 to 12 hours.

Its use has never been tested in a large clinical trial. However, the 2015 AVOID study, conducted in Australia, found that giving oxygen seemed to produce larger infarct sizes in STEMI patients. That trial enrolled only 441 patients.