Is Hyperoxic Ventilation Important to Treat Acute Coronary Syndromes Such As Myocardial Infarction?

Abstract

After reviewing the literature, I was unable to find hard evidence that the use of supplemental oxygen (hyperbaric or normobaric) in an uncomplicated acute myocardial infarction (AMI) is beneficial, and there is some evidence that it may be harmful. . © 2011 Wiley Periodicals, Inc.

Oxygen as a Vasoactive Substance

Because oxygen is a vasoactive substance, adverse responses to hyperoxia can occur, and the literature suggests that they are more common in patients with uncomplicated myocardial infarction (ie, no heart failure or cardiogenic shock).1 Hyperoxia is also a potent vasoconstrictor stimulus to the coronary circulation, particularly to the microcirculation.2 Hyperoxia may also exacerbate production of oxygen‐free radicals and thus exacerbate reperfusion injury.3

Treatment of Acute Myocardial Infarction, Then and Now

It is important to recall that medical therapy for acute myocardial infarction in the 1960s through the 1980s was not comparable to medical therapy in 2011. For example, nitrates, β‐blockers, thrombolysis, percutaneous intervention with stents, aspirin therapy, or other antiplatelet agents were not routinely used. Thus, the use of supplemental oxygen in those days may not be generalizable to current clinical practice.

Some Recent Literature Related to Oxygen Therapy of AMI

In 1997, 50 patients with myocardial infarction were reported who had received thrombolysis with streptokinase within 6 hours after onset of symptoms and were then randomized to normobaric oxygen or room air.4 Of those who received oxygen, 4.5% had at least 1 occurrence of oxygen saturation below 80% compared to 35% of those who were randomized to receive room air. Thus, in the circumstance of uncomplicated myocardial infarction, there may be intermittent episodes of hypoxemia detected by oximetry. When and if hypoxemia occurs, supplemental oxygen can be administered to raise the percent of oxygen saturation. Many recommend that oxygen should be administered to keep the saturation around 96% in patients with uncomplicated myocardial infarction.

A systematic review of the routine use of normobaric oxygen in the treatment of myocardial infarction was reported in 2009.5 The investigators concluded that the “limited evidence that exists suggests that the routine use of high‐flow normobaric oxygen in uncomplicated myocardial infarction may result in a greater infarct size and possibly increase the risk of mortality.”

Hyperbaric Oxygen

In patients with uncomplicated or even complicated myocardial infarction, hyperbaric oxygen is not commonly used in clinical practice. It has been hypothesized that the effects of hyperbaric oxygen may differ somewhat from normobaric oxygen delivery in these patients.

The study, called HOT MI, assessed the safety and feasibility of using hyperbaric oxygenation in 112 human subjects with acute myocardial infarction treated with recombinant tissue plasminogen activator or streptokinase.6 In this trial, the patients who received hyperbaric oxygen had a nonsignificant decrease of creatine kinase (CK) at 12 and 24 hours. Although treatment with hyperbaric oxygen in combination with thrombolysis appears to be feasible and safe for patients with AMI, outcomes such as CK rise, resolution of pain, and improved ejection fractions were not statistically significant findings. There is no good evidence that people are more likely to survive following hyperbaric oxygen therapy.

Summary

Controlled randomized human studies have failed to support the need for supplemental oxygen in uncomplicated myocardial infarction.7 These studies should not lead one to withhold supplemental oxygen in patients with acute pulmonary edema and low oxygen saturations or in patients whose oxygen saturation drops below 90%. Oxygen must be recognized as a vasoactive substance, and therefore it is a drug that may have detrimental effects in patients whose oxygen saturation is 95% or greater.

Hyperbaric oxygen in patients with acute myocardial infarction treated with thrombolysis failed to show a significant difference in endpoints, such as attenuated CK rise, more rapid resolution of pain, and improved ejection fractions.

Despite the guideline recommendation that supplemental oxygen in the first 6 hours in acute uncomplicated myocardial infarction is acceptable, the level of evidence for the use of normobaric oxygenation in uncomplicated acute myocardial infarction patients who are not hypoxemic is based on expert opinion, case studies, and standard of care.

Conclusion

Why use a treatment that costs money, has not been shown to be beneficial, and may be detrimental in some patients with uncomplicated myocardial infarction who have not demonstrated hypoxemia? Using supplemental oxygen in patients whose oxygen saturation is 95% or greater seems out of line with the main reason for using oxygen in a any patient (ie, hypoxia).