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  • Writer's pictureSaving Grace Medical Academy Ltd

Understanding Hyperoxia and Its Impact on Coronary Arteries: Revisiting Oxygen Therapy in ACS Patients

Hyperoxia and Coronary Arteries

Hyperoxia, or the condition of having excess oxygen in the body tissues, has traditionally been considered beneficial, especially in medical emergencies. However, recent studies and clinical guidelines have started to challenge this assumption, particularly concerning its effects on the coronary arteries and overall cardiac function.

Acute Coronary syndromes vs Hyperoxia

Coronary Arteries and Hyperoxia

The coronary arteries are responsible for supplying oxygen-rich blood to the heart muscle. Under normal conditions, these arteries maintain a delicate balance to ensure optimal oxygen delivery to meet the metabolic demands of the heart. Hyperoxia disrupts this balance, leading to several adverse effects on the coronary arteries:

  1. Vasoconstriction: Excess oxygen can cause the coronary arteries to constrict, reducing blood flow to the heart muscle. This paradoxically decreases the oxygen supply to the myocardium despite the increased oxygen content in the blood.

  2. Oxidative Stress: High levels of oxygen can increase the production of reactive oxygen species (ROS), leading to oxidative stress. This stress can damage endothelial cells lining the coronary arteries, impairing their function and contributing to atherosclerosis progression.

  3. Inflammation: Hyperoxia can trigger inflammatory responses within the coronary arteries. Chronic inflammation is a known contributor to the development and destabilization of atherosclerotic plaques, potentially leading to acute coronary events.

Pathophysiology of Acute coronary syndrome.
Pathophysiology of Acute coronary syndrome. - Curtesy of the Heart & Stroke Foundation ACLS

Rethinking Oxygen Therapy in Acute Coronary Syndrome (ACS)

Acute Coronary Syndrome (ACS) encompasses a range of conditions associated with sudden, reduced blood flow to the heart, including myocardial infarction (heart attack) and unstable angina. Traditionally, oxygen therapy has been a staple in the management of ACS patients, with the rationale that supplemental oxygen would improve oxygen delivery to ischemic heart tissues. However, recent evidence has prompted a reevaluation of this practice.

Why Oxygen for Every ACS Patient is No Longer Recommended

  1. Lack of Benefit in Non-Hypoxic Patients: Research, including large-scale randomized controlled trials, has shown that routine oxygen therapy in ACS patients without hypoxemia (normal blood oxygen levels) does not improve outcomes. In some cases, it may even be harmful by exacerbating oxidative stress and coronary vasoconstriction.

  2. Potential Harm: As previously discussed, hyperoxia can induce coronary vasoconstriction and oxidative stress, potentially worsening ischemic injury. Studies have indicated that patients receiving unnecessary oxygen therapy may have an increased risk of infarct size extension and adverse cardiac events.

  3. Guideline Updates: Reflecting these findings, major cardiology guidelines, such as those from the American Heart Association (AHA) and the European Society of Cardiology (ESC), now recommend that oxygen should only be administered to ACS patients with evidence of hypoxemia (SpO2 < 90%), respiratory distress, or other signs of hypo-perfusion.

What did we learn?

The evolving understanding of hyperoxia's impact on coronary arteries and the outcomes of ACS patients has led to significant changes in clinical practice. While oxygen remains a critical therapy for patients with hypoxemia, its routine use in all ACS patients is no longer recommended due to the lack of benefit and potential for harm. These insights underscore the importance of personalized medical care and the continuous reevaluation of established treatments in light of new evidence.

By adopting a more nuanced approach to oxygen therapy, healthcare providers can better protect the delicate balance within the coronary arteries and improve outcomes for patients experiencing acute coronary events.

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