High Flow Oxygen May Not Help Patients With Suspected Acute Coronary Syndrome

Patients with suspected acute coronary syndrome don't have better 30-day mortality outcomes when they receive high flow oxygen, a randomized trial has found.

Researchers examined data on 40,872 patients in New Zealand with suspected or confirmed acute coronary syndrome episodes, half of whom received high flow oxygen; the others were managed using a low-flow oxygen protocol.

Among patients with suspected acute coronary syndrome, 30-day mortality was similar with high flow oxygen (3.0%) and low flow oxygen (3.1%).

For the 4,159 patients diagnosed with ST elevation myocardial infarction (STEMI), 30-day mortality was slightly lower with high flow oxygen (8.8%) than with low flow oxygen (10.6%). Among non-STEMI patients, 30-day mortality was similar with high flow oxygen (3.6%) and low flow oxygen (3.5%).

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"In our study most people presenting with a suspected heart attack had normal oxygen blood levels and no benefit from oxygen, but the evidence is less certain when blood oxygen levels are low," said Dr. Ralph Stewart, a cardiologist and professor of medicine at Auckland City Hospital and the University of Auckland in New Zealand and coauthor of the study report published in The BMJ.

The results underscore that treatment for a heart attack must focused on interventions proven to make a difference, Dr. Stewart said by email.

"Knowledge that oxygen is neither beneficial nor harmful allows clinicians to focus more on the things we know make a difference," he said.

One limitation of the study is that it included patients regardless of whether they had an indication for oxygen, and regardless of whether they ultimately received a diagnosis of acute coronary syndrome, the researchers acknowledge. They also lacked data on oxygen use and protocol adherence.

"In patients who are hypoxic, we should give them oxygen supplementation. It's easy to measure for hypoxia," said Dr. J. William McEvoy, a professor of preventive cardiology at National University of Ireland Galway School of Medicine.

"However, for the vast majority of acute coronary syndrome patients who are not hypoxic, the data consistently show no benefit to indiscriminate provision of oxygen and that, in some cases among the sickest patients, excess oxygen administration may even be harmful," Dr. McEvoy, who wasn't involved in the study, said by email.

The subset of patients with suspected acute coronary syndrome who might benefit from supplemental oxygen also includes those with cyanosis, oxygen saturation below 90%, respiratory distress, or other high-risk features for hypoxemia, said Dr. KoKo Aung of Texas Tech University Health Sciences Center at El Paso.

"These patients can be readily identified by clinical examination and pulse oximetry monitoring in both the pre-hospital setting and the hospital setting," Dr. Aung, who wasn't involved in the study, said by email. "In the absence of evidence of proven benefit of high flow oxygen in people with acute coronary syndrome, in the background of presence of high quality evidence of potential harm in acutely ill adults, high flow oxygen should be avoided except in this subset of patients."

—Lisa Rapaport

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