Routine oxygen therapy in myocardial infarction--primum non nocere
It has been a concern reading from afar the recent editorial comment
[1,2] proposing that there is no convincing evidence of harm with the
routine administration of oxygen in myocardial infarction. We suggest
that this statement is not consistent with available evidence. We also
suggest that the relevant issue to consider is the balance of available
evidence for both the efficacy and safety of oxygen therapy in the routine
treatment of myocardial infarction.
Arterial oxygen tension is a major determinant of coronary artery
tone, with any increment in arterial oxygen content reducing coronary flow
regardless of initial saturation. In human studies of subjects with
cardiac disease, hyperoxia from high concentration oxygen therapy causes a
marked reduction in coronary blood flow . In patients with myocardial
infarction, high concentration oxygen therapy also causes a reduction in
cardiac output and stroke volume, and increases systemic vascular
resistance and blood pressure.
There is little evidence by which to determine the efficacy and
safety of high concentration oxygen therapy in myocardial infarction [4-
6]. The evidence that does exist indicates that the use of high
concentration oxygen therapy in uncomplicated myocardial infarction
results in a significant increase in infarct size (as determined by
cardiac enzyme levels)  and possibly mortality with an odds ratio of
death of 3.03 (95% CI 0.93 to 9.83) .
In terms of resuscitation following cardiac arrest, oxygen therapy
resulting in hyperoxia is independently associated with increased
mortality, compared with either hypoxia or normoxia .
As a result, there is no convincing evidence of benefit with the
routine use of oxygen therapy in myocardial infarction, and indeed, the
balance of the limited evidence that does exist suggests potential harm
with this approach. We propose from afar that the current recommendation
of the New Zealand Branch of the Cardiac Society of Australia and New
Zealand, that “oxygen should be administered to keep the saturations
around 96%”  is evidence-based and sound advice. We also refer
clinicians to the excellent British Guidelines on Oxygen Therapy which
recommend that oxygen should be prescribed for defined indications in
which the benefits outweigh the risks, and that the dose, method and
duration of delivery is specified and the patient’s response to oxygen
therapy is monitored .
1. Atar D. Should oxygen be given in myocardial infarction? BMJ
2010; 340: c3287.
2. Atar D. Oxygen for myocardial infarction. BMJ 2010; 340: (Letter).
3. Farquhar H, Weatherall M, Wijesinghe M, Perrin K, Ranchord A, Simmonds
M, Beasley R. Systematic review of studies of the effect of hyperoxia on
coronary blood flow. Am Heart J 2009; 158:371-7.
4. Wijesinghe M, Perrin K, Ranchord A, Simmonds M, Weatherall M, Beasley
R. Routine use of oxygen in the treatment of myocardial infarction:
systematic review. Heart 2009; 95:198-202.
5. Rawles JM, Kenmure AC. Controlled trial of oxygen in uncomplicated
myocardial infarction. BMJ 1976; 1: 1121-3.
6. Cabello JB, Burls A, Emparanza JI, Bayliss S, Quinn T. Oxygen therapy
for acute myocardial infarction (Review). The Cochrane Library 2010,
Issue 6. 2010: The Cochrane Collaboration, John Wiley & Sons Ltd.
7. Kilgannon JH, Jones AE, Shapiro NI, Angelos MG, Milcarek B, Hunter K,
et al. Association between arterial hyperoxia following resuscitation from
cardiac arrest and in-hospital mortality. JAMA; 303:2165-71.
8. ST-Elevation Myocardial Infarction Guidelines Group and the New Zealand
Branch of the Cardiac Society of Australia and New Zealand. ST-elevation
myocardial infarction: New Zealand management guidelines. NZMJ 2005;118:1
9. O'Driscoll BR, Howard LS, Davison AG, British Thoracic S. BTS guideline
for emergency oxygen use in adult patients. Thorax 2008; 63 Suppl 6:vi1-
Competing interests: No competing interests