August 29, 2011

August 29, 2011 (Paris, France) — After listening to the evidence, more cardiologists believe oxygen is harmful rather than helpful in MI patients, according to a poll of the audience at a debate on the subject today at the European Society of Cardiology (ESC) 2011 Congress. Despite this, almost everyone in the audience said oxygen is still routinely given to all MI patients in their hospitals.

While everyone seemed to agree that a large-scale trial is needed, taking the protagonist role for giving oxygen, Dr Jose Lopez-Sendon (La Paz University Hospital, Madrid, Spain) suggested that such a trial may be difficult to conduct because in an emergency situation it would be hard to obtain consent from a patient to participate in a study in which they might not get a treatment that has long been assumed to be beneficial.

However, after all the arguments for and against oxygen had been heard, there was an almost unanimous "yes" from the audience when asked by session chair Dr Salim Yusuf (McMaster University, Hamilton, ON) whether they would consent to participate in such a trial if they were an MI patient.

The two debaters had a difficult job reviewing the data for or against the use of oxygen as so few trials have been conducted, and those that have been done lack the size or quality to produce meaningful information. While there is a study in 300 patients now planned, Yusuf said this was not nearly large enough. "We need a 10 000-patient trial, not a 300-patient trial," he added.

We need a 10 000-patient trial, not a 300-patient trial.

Lopez-Sendon noted that in a recent survey 98% of health professionals said they routinely gave oxygen to MI patients because it is intuitive: "Myocardial ischemia is a lack of oxygen so it is logical to give oxygen."

He noted that although there are little hard data to support the use of oxygen in MI patients, a recent survey showed that 55% of health professionals believe oxygen reduces mortality in this situation, with only 1.3% saying they thought that it might be detrimental. He said the practice also gave the perception to patients and clinicians that something useful was being done, which reduced anxiety. In addition, most guidelines recommend oxygen for MI patients.

Reviewing the scientific evidence, Lopez-Sendon said it was conflicting, with some studies suggesting oxygen reduced ST changes, need for analgesics, severe hypoxemia, and infarct size, while other studies have suggested it increases coronary vascular resistance and heart rate and reduces cardiac output.

Brainwashed

Taking the antagonist view, Dr Chaim Lotan (Hadassah Hebrew University, Jerusalem, Israel) said there were "increasing data telling us not to use oxygen in MI patients."

"We have been brainwashed into using oxygen," but recent data suggest it causes harmful effects mainly mediated by vasoconstriction of the coronary arteries, he argued. "Before I started looking into the data, I didn't understand how much damage we were causing by giving oxygen."

Only three randomized studies of oxygen in MI patients have been conducted. As reported by heartwire , a recent meta-analysis of these studies in a Cochrane review showed the practice to be associated with a threefold increase in mortality, Lotan noted. "Oxygen is killing patients. It is a drug and should be evaluated as a drug," he concluded.

But Lopez-Sendon pointed out that the three studies included in the review had severe limitations, and there were only 13 deaths in total. "This is not enough to change practice. We don't have much data either way--to prove benefit or harm."

Lotan added that oxygen was one of several non–evidence-based practices--including leeches and cupping glasses--that have been used in MI patients. "Leeches and cupping glasses do not kill patients, but oxygen may do so."

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