Based on the results of the reviews by Dr Cabello and colleagues, the American Heart Association (AHA) issued guidelines that included a statement regarding oxygen therapy for AMI: “[T]here is insufficient evidence to support its routine use in uncomplicated ACS. If the patient is dyspneic, hypoxemic, or has obvious signs of heart failure, providers should titrate therapy, based on monitoring of oxyhemoglobin saturation, to 94% (Class I, Level of Evidence: C).”2
“Given the paucity of evidence highlighting the clinical efficacy of routine oxygen and the ever-increasing clinical and physiological data indicating the dangers of routine oxygen, robust contemporary clinical evidence of the benefits and potential harms of oxygen therapy are needed,” Dr Stub said.
Evidence for Oxygen Therapy in AMI
The uncertainty of whether oxygen therapy in AMI is beneficial or harmful has stimulated the development of clinical trials examining this question. Dr Cabello and colleagues conducted an updated review of the evidence for this practice, and their findings were recently published in the Cochrane Database of Systematic Reviews.1
Randomized controlled trials that compared oxygen therapy to room air in patients with suspected or proven AMI were included in the analysis. A total of 5 randomized controlled trials — one of which was new since 2013 and another since 2010 — met inclusion criteria for this review.1
Of 1173 participants with suspected or confirmed AMI, 32 (2.7%) died. No difference in all-cause mortality was found between the treatment groups in the overall population (pooled risk ratio [RR], 0.99; 95% CI, 0.50-1.95; 4 studies, N = 1123) or in patients with confirmed AMI (RR, 1.02; 95% CI, 0.52-1.98; 4 studies, N = 871).1
The only trial that measured cardiac mortality found a nonsignificant advantage with oxygen therapy vs room air (1.3% vs 2.2%; RR, 0.58; 95% CI, 0.17-1.95; N = 628). Rates of cardiac failure were also lower with oxygen in 2 studies, but this finding did not reach statistical significance (RR, 0.88; 95% CI, 0.50-1.55; N = 775).1
Oxygen therapy had no conclusive effect on other outcomes, including stroke, recurrence of myocardial ischemia, revascularization, major bleeding, pain, and infarct size.1
Although the results of the most recent Cochrane Review suggest that oxygen therapy does not provide added benefit in AMI, Dr Cabello pointed out that the overall quality of evidence examined was low.1
“Both trials published since the 2010 review used surrogate, rather than clinical, outcomes as the primary outcome. One used infarct size, as estimated by magnetic resonance imaging, and the other used creatine kinase levels,” Dr Cabello said in an interview with Cardiology Advisor. “Clinical outcomes, such as mortality, cardiac failure, cardiogenic shock, need for revascularization, and pericarditis, were considered as secondary outcomes in these studies.”
“Since primary outcomes are used to guide study design and sample size calculations, these 2 new studies, like the previous ones included in the 2010 review, did not have the power to demonstrate statistically significant effects on the outcomes, which are critical for clinical decision making,” he noted.
The Experts Weigh In
According to Dr Cabello, no firm recommendation can be made regarding oxygen therapy for AMI given the low quality and scarcity of the available clinical trial evidence. “The message for clinicians is that we still do not know if oxygen is helpful, harmful, or useless,” he said. “There are theoretical reasons why it could help and also why it could do harm.”
For practical purposes, until more trials are completed, Dr Cabello recommends following guideline recommendations to administer oxygen only in patients with AMI who have hypoxemia or respiratory distress.
“This updated Cochrane Review further emphasizes the message that oxygen should be treated like all other medical therapies, in which efficacy needs to be balanced with the side effect profile,” Dr Stub said.
Like Dr Cabello, he advocates using oxygen for AMI only in patients who need it according to the AHA guidelines. “Until larger studies are available, oxygen should not be routinely administered to patients unless oxygen saturations are less than 94%,” he said.
- Cabello JB, Burls A, Emparanza JI, Bayliss SE, Quinn T. Oxygen therapy for acute myocardial infarction. Cochrane Database Syst Rev. 2016;12:CD007160. doi: 10.1002/14651858.CD007160.pub4
- O’Connor RE, Brady W, Brooks SC, et al. Part 10: acute coronary syndromes: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(18 Suppl 3):S787-S817. doi: 10.1161/CIRCULATIONAHA.110.971028
- McNulty PH, Robertson BJ, Tulli MA, et al. Effect of hyperoxia and vitamin C on coronary blood flow in patients with ischemic heart disease. J Appl Physiol (1985). 2007;102(5):2040-2045.
- McNulty PH, King N, Scott S, et al. Effects of supplemental oxygen administration on coronary blood flow in patients undergoing cardiac catheterization. Am J Physiol Heart Circ Physiol. 2005;288(3):H1057-H1062.
- Rousseau A, Bak Z, Janerot-Sjöberg B, Sjöberg F. Acute hyperoxaemia-induced effects on regional blood flow, oxygen consumption and central circulation in man. Acta Physiol Scand. 2005;183(3):231-240.
- Cabello JB, Burls A, Emparanza JI, Bayliss S, Quinn T. Oxygen therapy for acute myocardial infarction. Cochrane Database Syst Rev. 2010;(6):CD007160. doi: 10.1002/14651858.CD007160.pub2
- Cabello JB, Burls B, Emparanza JI, Bayliss S, Quinn T. Oxygen therapy for acute myocardial infarction. Cochrane Database Syst Rev. 2013;8:CD007160. doi:10.1002/14651858.CD007160.pub3