Australian Financial Review
Doubt has been thrown on the routine practice of giving patients oxygen to inhale during a heart attack. There is no evidence this is always beneficial and a review of available evidence hints it may sometimes be harmful.
The review, by the Cochrane Collaboration, says the possibility that giving oxygen may actually increase a patient's risk of dying cannot be ruled out.
The Cochrane Collaboration, a group of 10,000 volunteers in 90 countries, conducts systematic reviews of medical evidence to help people make practical decisions.
In Australia, oxygen is routinely given all the way from the ambulance to the emergency department to the coronary care unit.
"Oxygen has an aura of `goodness' around it," says Garry Jennings, professor and director of Melbourne's Baker IDI Heart and Diabetes Institute.
It provides comfort because it gives patients and medical staff the feeling that something is being done. He says relatives often become quite distressed if the mask falls off when the patient moves.
While oxygen is often life saving, it doesn't always do good. In newborn babies very high concentrations can damage the eye. It can also cause a loss of consciousness in some people with lung disease.
With heart attacks, the issue is complicated. In some cases oxygen helps, in some it makes no difference and in others it seems it may cause harm.
A heart attack is caused by a blockage of a coronary artery. Simply increasing oxygen in the blood flowing around the body doesn't necessarily mean it will get to the heart muscle that needs it, says Jennings.
"There is also strong evidence that tissue damage during a heart attack can be aggravated by the production of `free radicals' which are the products of oxygen metabolism. So it is theoretically possible to make a case for or against oxygen in this situation."
A case can be made for oxygen in some heart attack patients with poor pumping in the left heart which causes fluid to build up in the lungs.
The fluid impairs the ability for oxygen to cross into the blood following each breath. Oxygen can readily help to correct this.
The Cochrane researchers reviewed three randomised trials involving almost 400 patients who were given pure oxygen or air to inhale in the 24 hours following the start of heart attack symptoms.
Only 14 died, but of them, almost three times as many had inhaled oxygen as opposed to air.
While the numbers are too small to depend on, more research is needed to resolve the uncertainty.
Administering oxygen during a heart attack has now become the latest example of an established clinical treatment which is based on good intentions and good assumptions, but for which there is no solid evidence.
So would Jennings continue to administer it?
"Yes in some patients. It is relatively easy to monitor the saturation of oxygen in the blood and I would certainly administer oxygen where this is low. However, I would not necessarily give it to others."