Is oxygen therapy necessary for all patients with acute coronary syndrome (ACS)?

Oxygen Therapy in Acute Coronary Syndrome

No, oxygen therapy is not needed in all patients with ACS—it should only be administered to patients with confirmed hypoxia (oxygen saturation <90%) and is not recommended for normoxic patients (oxygen saturation ≥90%) as it does not improve cardiovascular outcomes and may cause harm. 1

Evidence-Based Oxygen Administration Protocol

When Oxygen IS Indicated (Class I Recommendation)

• Administer supplemental oxygen to patients with oxygen saturation <90% to increase saturations to ≥90%, as this improves myocardial oxygen supply and decreases anginal symptoms. 1

• Oxygen is also indicated for patients with respiratory distress, signs of heart failure, shock, or other high-risk features of hypoxemia. 1

• Target oxygen saturation should be maintained at 90-96% to avoid both hypoxemia and hyperoxia. 2, 3

When Oxygen Should NOT Be Used (Class III: No Benefit)

• Routine administration of supplemental oxygen in patients with oxygen saturations ≥90% is not recommended because it does not improve cardiovascular outcomes. 1

• Multiple randomized trials have demonstrated lack of benefit with routine supplemental oxygen in normoxic ACS patients, with some evidence suggesting potential harm. 1, 4

Why This Recommendation Changed

The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guidelines represent a significant departure from historical practice, which routinely administered oxygen to all ACS patients regardless of saturation. 1

Evidence of Potential Harm

• Hyperoxia causes vasoconstriction in coronary, cerebral, and systemic vasculature, which paradoxically decreases regional blood flow and oxygen delivery despite higher arterial oxygen content. 2, 3

• The AVOID trial demonstrated that oxygen administration to normoxic STEMI patients increased myocardial injury at presentation, larger infarction size at 6 months, higher reinfarction rates, and increased cardiac arrhythmias. 1, 4

• Studies have shown increased coronary vascular resistance, reduced coronary blood flow, and potentially increased mortality risk with routine oxygen use in normoxic patients. 1, 3

• The relationship between oxygenation and outcomes is U-shaped, with lowest mortality observed at SpO2 of 94-96%. 4

Evidence of No Benefit

• The DETO2X-AMI trial found that supplemental oxygen did not reduce all-cause mortality or rehospitalization with MI in patients with suspected MI and oxygen saturation ≥90%. 4, 3

• Systematic reviews of randomized controlled trials showed no significant decrease in all-cause mortality (odds ratio 1.01; 95% CI 0.81-1.25) or reduction in infarct size with oxygen therapy in normoxic patients. 5

Clinical Algorithm for Oxygen Management

Step 1: Immediate Assessment

• Measure oxygen saturation immediately upon patient presentation using continuous pulse oximetry. 3
• Assess for respiratory distress, cyanosis, or signs of heart failure/shock. 1

Step 2: Decision Point Based on Saturation

If SpO2 <90%:

• Administer supplemental oxygen immediately via nasal cannula or mask. 1, 3
• Titrate to maintain SpO2 90-96%. 2, 3
• Consider arterial blood gas analysis if pulse oximetry may be unreliable. 2

If SpO2 ≥90%:

• Do NOT administer routine supplemental oxygen. 1, 4
• Continue monitoring with pulse oximetry. 3
• Reassess if clinical status changes. 1

Step 3: Escalation if Needed (for hypoxic patients)

• If severe respiratory distress or pulmonary edema develops, consider non-invasive ventilation. 4
• If significant hypoxemia persists despite supplemental oxygen, endotracheal intubation and mechanical ventilation may be required. 4

Critical Pitfalls to Avoid

• Do not administer oxygen "just to be safe" in normoxic patients—this practice is outdated and potentially harmful. 1, 4

• Avoid excessive oxygenation even in hypoxic patients, as mortality appears lowest at SpO2 94-96%, not higher levels. 4, 3

• In patients with chronic CO2 retention (e.g., COPD), excessive oxygen can worsen hypercapnia; use controlled oxygen delivery while monitoring both SpO2 and CO2 levels. 3

• Do not continue oxygen therapy beyond initial stabilization in patients who become normoxic without specific ongoing indications. 4

• Do not delay appropriate oxygen therapy in truly hypoxemic patients while waiting for additional testing. 4

• Be aware that nitroglycerin administration may increase ventilation-perfusion abnormalities, potentially worsening hypoxemia in some patients. 4

Special Populations

STEMI vs NSTEMI

The oxygen recommendations are consistent across both STEMI and NSTEMI presentations—only administer if SpO2 <90% or respiratory distress is present. 1, 3

Cardiac Arrest with ACS

For patients with STEMI and cardiac arrest, the same oxygen principles apply once return of spontaneous circulation is achieved—avoid hyperoxia in normoxic patients. 1