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# 7825
Supplemental oxygen has been a mainstay treatment by emergency rooms, ICUs, paramedics, and EMTs for decades, and is most often employed for shortness of breath and/or chest pain. But, as my old paramedic instructor warned more than 40 years ago, `Oxygen is a drug. And if administered improperly, can do more harm than good.”
The primary concern (four decades ago) was that patients with COPD receiving too much oxygen would suffer respiratory failure. The rule of thumb was no more than 2 to 3 liters of O2 for an emphysema (COPD) patient.
Sometime in the mid-1980s, the thinking changed, and it became standard protocol for a lot of EMS services not to deprive COPD patients in serious respiratory distress of high flow rates of oxygen. Running contrary to that opinion, in 2008 the British Thoracic Society came up with guidelines that restricted in-the-field oxygen delivery for COPD patients – and those were adopted by British Ambulance services in 2009.
That guideline recommended that oxygen be administered to patients whose oxygen saturation falls below the target saturation ranges (94-98% for most acutely ill patients and 88-92% for those at risk of type 2 respiratory failure with raised carbon dioxide level in the blood), and that those who administer oxygen therapy should monitor the patient and keep within those specified target saturation ranges.
But elsewhere in the world, delivery of high flow rates of oxygen for COPD patients (both pre-hospital and in-hospital) remained common.
In 2010, a study (Effect of high flow oxygen on mortality in chronic obstructive pulmonary disease patients in prehospital setting: randomised controlled trial) was published in the BMJ that looked at the outcomes of patients with COPD who received high flow oxygen (compared to those who did not), and found their 30 day survival rate was worse.
I described the study in BMJ: Oxygen Delivery and COPD, and while the study was small, and subject to other limitations, they found:
- Titrated oxygen treatment reduces mortality, acidosis, and hypercarbia in patients with acute exacerbation of chronic obstructive pulmonary disease treated before arrival at hospital
- The risk of death was reduced by 78% by use of titrated oxygen rather than high flow oxygen, with a number needed to harm of 14
- These findings provide strong evidence that titrated oxygen treatment should be used for hypoxic or breathless patients with chronic obstructive pulmonary disease in prehospital settings
Fast forward a little over a year (January 2012), and in a blog called Oxygen Delivery & The Emergency Patient: Revisited, we looked at a retrospective study that appeared in the Archives of Internal Medicine that lent weight to the argument that when it comes to oxygen for emergency patients, less may be more.
Supplemental Oxygen Therapy in Medical Emergencies: More Harm Than Benefit?
Alexander D. Cornet, MD; Albertus J. Kooter, MD; Mike J. L. Peters, MD, PhD; Yvo M. Smulders, MD, PhD
Arch Intern Med. Published online January 9, 2012. doi:10.1001/archinternmed.2011.624
Smulders' team reviewed 18 previously conducted studies that looked at patient outcomes following oxygen treatment for common medical emergencies that included heart attacks, strokes, cardiac arrest, and COPD.
What they claim to have found is little or no evidence that high-dose oxygen improves survival, and weak evidence that it may even be detrimental.
And not just for COPD patients.
The authors suggest that hyperoxia (excessive oxygen levels in the lungs, blood, or tissues) may cause hemodynamic changes that may actually increase myocardial ischemia (depriving heart muscle of oxygen) during a heart attack. They also propose that a relationship exists between hyperoxia and greater mortality and complications in non-cardiac emergencies as well.
All of which brings us to a new Cochrane Review, conducted by researchers at The University of Surrey and The City University London, that questions whether emergency oxygen is therapeutic for heart attack victims, and suggests it may even be detrimental.
First stop, the Cochrane review summary, then excerpts from the University of Surrey press release, after which I’ll return with a bit more.
Routine use of oxygen in people who have had a heart attack Updated
Cabello JB, Burls A, Emparanza JI, Bayliss S, Quinn T
Published Online:
August 21, 2013
(EXCERPT)
We found four randomised controlled trials that compared one group given oxygen to another group given air. These trials involved a total of 430 participants of whom 17 died. In that group, more than twice as many people known to have been given oxygen died compared to those known to have been given air. However, because the trials had few participants and few deaths, this result does not necessarily mean that giving oxygen increases the risk of death. The difference in numbers may have occurred simply by chance. Nonetheless, since the evidence suggests that oxygen may in fact be harmful, we think it is important to evaluate this widely-used treatment in a large trial as soon as possible, to make sure that current practice is not causing harm to people who have had a heart attack.
The Cochrane review process involves examining existing studies, eliminating those that do not meet certain strict standards, and then analyzing the results of those studies that they believe are well-mounted. While the intent is only to rely on `the best scientific evidence’, this process can winnow down the field of research to the point where there is insufficient data on which to make a determination.
And basically, that’s where this issue stands. In their abstract, the author’s write::
There is no conclusive evidence from randomised controlled trials to support the routine use of inhaled oxygen in people with AMI. A definitive randomised controlled trial is urgently required, given the mismatch between trial evidence suggestive of possible harm from routine oxygen use and recommendations for its use in clinical practice guidelines.
In other words, we haven’t enough high quality studies to conclude – one way or the other – whether oxygen is helpful or detrimental to the heart attack victim. Although I’d have put it in the lede, that assessment appears about 3/4ths of the way down the University of Surrey’s press release, in the following caveat:
Currently the number of participants involved is too low to enable conclusions about the effectiveness or harms of oxygen to be drawn.
Here are some excerpts from the press release. Follow the link to read it in its entirety.
No evidence to support giving oxygen to people having a heart attack, research shows
Monday 30 September 2013
Research shows that oxygen therapy following a heart attack may do more harm than good.
For 100 years inhaled oxygen has been a standard treatment for those with a suspected or confirmed heart attack. The latest research, was led by academics from City University London and the University of Surrey, suggests that oxygen therapy may be doing more harm than good.
More than seven million people – worldwide - die each year from coronary heart disease (CHD) and it is now the leading cause of death in the UK and US. A heart attack, or acute myocardial infarction, is often the first manifestation of CHD and a timely and appropriate intervention can make a significant difference to mortality rates.
However, more than three years on from their first call for further research on the use of oxygen therapy, there are still wide variations in practice and the possibility that patients are either being harmed or deprived of benefit.
Professor Tom Quinn, from the University of Surrey, comments: “While the changes to international guidelines for heart attack following our 2010 review are welcome, this new review suggests that we still do not have an evidence-based answer, based on an adequately powered and well conducted randomised trial, to confirm to clinicians and patients the role of oxygen therapy in heart attack treatment. It is likely that a global collaboration will be required to deliver such a trial.”
Professor Amanda Burls, from City University, said: “Our first review in 2010 on this topic called for more research to find out whether oxygen was useful or harmful.
“While the review had a huge impact on practice, with many national and international guidelines changing from recommending routine use of oxygen to recommending it not to be used routinely, funding to run a trial to settle this important uncertainty has not yet been forthcoming.”
Amazingly, after a century of routine use, we don’t really know whether oxygen therapy is a help or a hindrance during a heart attack. The lack of well-mounted studies showing its efficacy isn’t enough to condemn it use, of course.
But when coupled with other studies that suggest some degree of harm from oxygen is possible, and with the fate of millions of people each year in the balance, the need for better scientific evidence becomes glaringly obvious.
Stay tuned.
