Oxygen and heart attack - what next?
Most medical students will recognize the quote:
‘Half of what you'll learn in medical school will be shown to be either dead wrong or out of date within five years of your graduation; the trouble is that nobody can tell you which half—so the most important thing to learn is how to learn on your own.’
Dave Sackett: “Old fart from the frozen north” “Father of EBM”
The rapid assessment and treatment of a patient with a heart attack is drummed into most medical students very early on in their training. ABC: airway, breathing, circulation. Part of that resuscitation is the delivery of Oxygen to patients with a heart attack, mainly due to the fact the flow of oxygenated blood in the heart is stopped for a period of time.
The idea for providing oxygen in a heart attack is it may improve the amount of oxygen of the cells in the heart that are dying mainly due to the lack of oxygen, ultimately reducing pain and the size of the dead heart muscle. To most this will make sense in terms of pathophysiological reasoning.
Today a Cochrane review by Cabello and Burls on Oxygen therapy for acute myocardial infarction looks at the evidence from randomised controlled trials to establish whether routine use of inhaled oxygen in acute heart attack infarction improves patient-centred outcomes, in particular pain and death.
Now, here is the half of what is learnt learn that may eventually be out of date:
Three trials involving 387 patients were included and 14 deaths occurred. The pooled relative risk of death was 2.88 (95% confidence interval 0.88 to 9.39) in an intention-to-treat analysis and 3.03 (95% confidence interval 0.93 to 9.83) in patients with confirmed heart attack.
While suggestive of harm, the small number of deaths recorded meant that this could be a chance occurrence. Basically, there is no conclusive evidence from randomised controlled trials to support the routine use of inhaled oxygen in patients with acute heart attack.
The neat thing about EBM is you are never really sure of which half is out of date; this review adds to that half. As the reviewers rightly state, we need an urgent large scale trial to unpick the uncertainty.