NEW YORK - That oxygen mask they strap on patients rushed to the ER after a heart attack or a stroke? It could be doing more harm than good in many cases, Dutch researchers say in a new report.
In a review of earlier research, they found no support for routinely giving critically ill patients high-dose oxygen, a common practice among paramedics and emergency physicians.
"There is not a single study that points to beneficial effects," said Dr. Yvo Smulders, a professor at VU University Medical Center in Amsterdam. "All of the evidence that we found points to detrimental effects."
Most doctors believe extra oxygen is life-saving and many guidelines recommend it, he and his colleagues write in the Archives of Internal Medicine.
"What you would expect is that oxygen is healthy," Smulders told Reuters Health. "But it seems that God didn't introduce 20 per cent oxygen in room air for nothing."
Studies on animals dating to the 1960s and 70s have found that higher-than-normal oxygen levels could be dangerous.
Smulders' team gathered all the human research they could find on supplemental oxygen after heart attacks, strokes, cardiac arrest and acute attacks of chronic obstructive pulmonary disease, or COPD.
The 18 studies they came up with all had the same grim message: supplemental oxygen doesn't work, and there is some weak evidence that it might be harmful.
For instance, one trial from 1976 found nine out of 80 heart attack patients who got oxygen died, compared to just 3 out of 77 who got compressed air. Although that difference could have been a statistical fluke, it was still bad news for oxygen.
Another trial, this one in stroke patients, had to be stopped early because too many patients who got extra oxygen died.
And for cardiac arrest, in which the heart stops beating, a study out last year found that people who had a lot of oxygen in their blood after they were revived died more often than people with normal levels.
"It has potentially far-reaching implications, because supplemental oxygen is just ubiquitous in the care of critically ill patients," Dr. Stephen Trzeciak, who led that work, told Reuters Health.
Too much oxygen in the blood can lead to the formation of molecules known as free radicals, he said, which can damage organs such as the heart and the brain.
But this is still theory, Trzeciak warned, and so far there is no iron-clad proof that supplemental oxygen is harmful. What is clear is that too little oxygen can be lethal.
"My concern is, if we just indiscriminately stop giving supplemental oxygen to post-arrest patients, they might end up having low oxygen, which is just as harmful or more harmful" than high oxygen, said Trzeciak, who studies resuscitation at Cooper University Hospital in Camden, New Jersey.
The American Heart Association currently recommends giving supplemental oxygen to people with cardiac arrest until the heart is restarted.
At that point, the group urges doctors and paramedics to use measurements to ensure that oxygen levels in the blood don't get too high. The same goes for heart attacks.
But what often happens is that providers just leave the oxygen on full blast, according to Dr. Michael Sayre of the American Heart Association.
"They don't realize they are giving too much oxygen," Sayre told Reuters Health. "It's just not something they are paying attention to."
The Dutch researchers call for more studies. But until then, Smulders said, health providers should only give oxygen when blood levels are very low and they should make sure they never become too high.
"I think it is about time that you step away from your intuitive approach and look at the evidence," he said.