When should a patient with ST-elevation myocardial infarction (STEMI) and a history of cardiovascular disease be hooked up to oxygen (O2) support?

Oxygen Therapy in STEMI: Evidence-Based Indications

Administer supplemental oxygen to STEMI patients only when oxygen saturation (SpO2) is <90%, or when they present with hypoxemia, breathlessness, acute heart failure, or cardiogenic shock—routine oxygen therapy in normoxemic patients (SpO2 ≥90%) is not recommended and may be harmful. 1, 2

Clear Indications for Oxygen Therapy

Oxygen therapy is indicated in the following specific situations:

• Hypoxemia with SpO2 <90% or PaO2 <60 mmHg 1, 2
• Breathlessness or respiratory distress 1, 2
• Acute heart failure or pulmonary edema 1, 2
• Cardiogenic shock 1

The 2017 ESC Guidelines provide the strongest recommendation, stating oxygen is indicated (Class I, Level C) in patients with hypoxemia (SaO2 <90%), while explicitly stating routine oxygen is NOT recommended (Class III, Level B) when SaO2 ≥90%. 1

Evidence Against Routine Oxygen in Normoxemic Patients

The evidence strongly argues against routine oxygen administration in STEMI patients with normal oxygen saturation:

• The 2013 ACC/AHA Guidelines note that a pooled Cochrane analysis of 3 trials showed a 3-fold higher risk of death for patients with confirmed acute MI treated with oxygen compared to those managed on room air 1
• Multiple randomized trials demonstrate no cardiovascular benefit with routine supplemental oxygen in patients with SpO2 ≥90%, and studies suggest worse short- and long-term mortality with liberal oxygen administration 2
• The AVOID trial demonstrated that supplemental oxygen in STEMI patients with oxygen saturations ≥94% not only lacked benefit but showed possible increase in myocardial injury and infarct size 2
• Supplementary oxygen may increase coronary vascular resistance, potentially worsening outcomes 1

Optimal Oxygen Saturation Target

The relationship between oxygenation and outcomes is U-shaped, with the lowest mortality observed at SpO2 of 94-96% at presentation. 2 This means both hypoxemia AND hyperoxemia are potentially harmful.

Practical Algorithm for Oxygen Administration

Follow this stepwise approach:

1. Immediately measure SpO2 upon first medical contact 2

2. If SpO2 <90%: Administer supplemental oxygen via nasal cannula or mask to maintain SpO2 ≥90% 2

3. If SpO2 ≥90%: Do NOT administer routine oxygen 1, 2

4. If severe respiratory distress or pulmonary edema despite adequate SpO2: Consider non-invasive ventilation 2

5. If severe hypoxemia not corrected by supplemental oxygen: May require endotracheal intubation and mechanical ventilation 2

Critical Pitfalls to Avoid

Common errors in oxygen management include:

• Administering routine oxygen to all STEMI patients regardless of saturation—this outdated practice may increase mortality and infarct size 1, 2
• Failing to continuously monitor oxygen saturation during initial stabilization 2
• Delaying appropriate oxygen therapy in truly hypoxemic patients 2
• Continuing oxygen therapy beyond initial hours in normoxemic patients without specific indications 2
• Using high-flow oxygen in patients with chronic obstructive pulmonary disease, which may cause respiratory depression 1, 2

Special Considerations

In patients with cardiogenic shock complicating STEMI:

• Oxygen/mechanical respiratory support is indicated according to blood gases (Class I, Level C) 1
• These patients often require more aggressive respiratory support given their hemodynamic instability 1

Caution with concurrent medications:

• Nitroglycerin administration may increase ventilation-perfusion abnormalities, potentially worsening hypoxemia 2
• Morphine use for pain relief is appropriate but monitor respiratory status closely 1