Providing oxygen in the treatment of acute coronary syndrome (ACS) is often done to increase oxygen supply to cells experiencing hypoxia. One of the complications of hypoxia is brain cell ischemia. However, the benefits of oxygen therapy in treating ACS cases without hypoxia are still being studied, whether beneficial or harmful.

Should all Acute Coronary Syndrome cases need Oxygen?

Patients suspected of having Acute Coronary Syndrome need MONA therapy (morphine, oxygen, nitroglycerin, aspirin). Recommendations for administering oxygen are in the following conditions:
  • Arterial O2 saturation <95% or respiratory distress (class I-C recommendations)
  • All SKA patients within the first 6 hours, without consideration of arterial O2 saturation (class IIa-C)

Whereas the AHA (American Heart Association) recommends giving oxygen to:
  • NSTEMI (non-ST elevation myocardial infection): given to patients with cyanosis, arterial O2 saturation <90%, respiratory distress or other hypoxaemic states, and in the first 6 hours without arterial O2 saturation status.
  • STEMI: hypoxemic patients (O2 saturation <90%), heart failure, and dyspnea.

In fact, administration of oxygen is still often done in myocardial infarction regardless of the onset and saturation of oxygen.



Rational Administration of Oxygen in Myocardial Infarction

Myocardial infarction is caused due to an imbalance of oxygen demand and supply to the heart muscle. Providing additional oxygen aims to increase the supply of oxygen to the heart muscle so that infarction does not diffuse, and other complications do not occur.

Oxygen supplementation can increase oxygen pressure in the blood to above 60 mmHg. Oxygen and hemoglobin dissociation curves at high pressure tend to be flat against oxygen saturation. Thus, oxygen saturation in the blood does not change significantly to oxygen pressure that is too high. Increased oxygen in the blood gives a side effect that is called reactive oxygen species (ROS).

ROS are highly reactive molecules that can cause significant damage to cells. ROS's effects can make arrhythmias due to faster depolarization, cell death, and vasoconstriction. These arrhythmias aggravate ischemia, increase systemic vascular resistance, and lead to heart failure.

In a Swedish study involving more than 6000 patients, oxygen administration during acute myocardial infarction did not reduce mortality after one year.

In patients with acute myocardial infarction with saturation above 90%, the first group was given 6 liters of oxygen per minute, and the second group was given room air.

The results of this study, the comparison between patients receiving therapy with room air versus oxygen did not differ significantly in terms of length of stay (p = 0.87), recurrence of recurring infarction (p = 0.72), new atrial fibrillation (p = 0.53), atrioventricular block degrees 2 and 3 (p = 0.24), cardiogenic shock (p = 0.17) and death (p = 0.35)

In the Cochrane study involving 5 studies on oxygen use and room air in myocardial infarction, 1173 respondents found 32 respondents died. The mortality rate was not much difference between the oxygen group and the room air. 

The risk ratio of death from all causes between oxygen and free air groups was 0.99 (95% CI, 0.50 - 1.95), and 1.02 (95% CI 0.52 - 1.98) for events that were confirmed as acute myocardial infarction. So it cannot be concluded whether oxygen can give advantages or disadvantages to acute myocardial infarction, and the side effects are unknown.

The AVOID (Water versus Oxygen in Myocardial Infarction) study uses cardiac enzymes to measure the extent or extent of myocardial infarction. Heart enzymes used include creatinine kinase (CK) and troponin. Studies with cardiac enzymes found:
  • CK peak levels were significantly higher in the oxygen group than in room air (1948 u / L vs 1543 u / L; means ratio: 1.27; 95% CI 1.04 - 1.52, p = 0.01)
  • Troponin peak levels were not significantly different (57.4 mcg / L vs 48.0 mg / L; ratio: 1.20; 95% CI, 0.92 - 1.56; p = 18%).


The further results observed were:
  • The incidence of myocardial infarction was more frequent in the oxygen group (5.5% vs 0.9%, p = 0.006)
  • Cardiac arrhythmias were higher in the oxygen group (40.4% vs 31.4%; p = 0.05).
  • The area of ​​myocardial infarction measured by cardiac magnetic resonance after 6 months was higher in the oxygen group (20.3 g vs 13.1 g; p = 0.04)



Conclusion

Providing oxygen to Acute Coronary Syndrome with oxygen saturation above 95% needs to be considered the advantages and disadvantages. In various randomized controlled trial studies, oxygen was found to be of no use.

In the AVOID study, extensive infarcts were measured through cardiac enzymes (CK and troponin) and cardiac magnetic resonance, the incidence of recurrent myocardial infarction, and arrhythmias were found to be higher in the oxygen-administered group. Possible adverse effects are cell damage and vasoconstriction due to ROS.

So, not all cases of Acute Coronary Syndrome need oxygen administration. Acute Coronary Syndrome with oxygen saturation above 95% does not need oxygen administration.