What are the effects of using supplemental oxygen when you don't need it?

Effects of Using Supplemental Oxygen When You Don't Need It

If you use supplemental oxygen when you don't need it (i.e., when your oxygen saturation is normal at ≥90%), you may experience increased harm including larger heart attack size, increased cardiac arrhythmias, and potentially worse mortality outcomes. 1

Evidence of Harm in Normoxic Patients

Cardiovascular Effects

• The AVOID trial demonstrated that oxygen administration in STEMI patients with oxygen saturations ≥94% resulted in increased myocardial injury at presentation, larger infarction size at 6 months, increased reinfarction rates, and increased incidence of cardiac arrhythmias. 1
• The DETO2X-AMI trial evaluated 6,629 patients with suspected MI and oxygen saturation ≥90% and found that supplemental oxygen did not reduce all-cause mortality at 1 year or rehospitalization with MI. 1
• The relationship between oxygenation and outcomes is U-shaped, with the lowest mortality rate occurring in patients with SpO₂ of 94% to 96% at presentation—meaning both too little AND too much oxygen are harmful. 1

Mechanism of Harm

• Hyperoxia causes vasoconstriction in cerebral, coronary, and systemic vasculature, which can paradoxically decrease regional oxygen delivery despite increased arterial oxygen content. 2
• If perfusion decreases more than arterial oxygen content increases during hyperoxia, regional oxygen delivery actually decreases. 2
• Hyperoxia increases production of reactive oxygen species and related oxidative stress. 3
• Hyperoxia reduces coronary blood flow and myocardial oxygen consumption through vasoconstriction. 3

Current Guideline Recommendations

What NOT to Do

• The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guidelines explicitly recommend NOT using routine supplemental oxygen in patients with acute coronary syndromes who have normal oxygen saturation (SpO₂ ≥90%). 1, 4
• The 2015 American Heart Association guidelines state that withholding supplementary oxygen therapy in normoxic patients is reasonable in prehospital, ED, and hospital settings. 1
• Studies have suggested worse short- and long-term mortality with liberal compared to conservative administration of supplemental oxygen in patients without hypoxia. 1

When Oxygen IS Indicated

• Oxygen therapy is clearly indicated for patients with hypoxemia (SpO₂ <90% or PaO₂ <60 mmHg). 4
• Oxygen should be administered to patients with breathlessness, signs of heart failure, shock, or respiratory distress. 1, 4
• Specific conditions where oxygen may be beneficial include decompression sickness and advanced cancer patients with both dyspnea AND hypoxemia. 1

Clinical Pitfalls to Avoid

Common Mistakes

• Administering oxygen "just to be safe" in normoxic patients can cause actual harm rather than providing a safety margin. 1
• Continuing oxygen therapy beyond initial stabilization in normoxemic patients without specific indications is a common error. 4
• Failing to monitor oxygen saturation continuously and adjust therapy accordingly. 4
• Assuming that "more oxygen is always better"—this outdated belief is contradicted by modern evidence. 2, 5, 6, 7

Specific Populations at Risk

• Patients with COPD may experience respiratory depression with high-flow oxygen and are vulnerable to carbon dioxide retention. 4, 7
• Post-cardiac arrest patients show worse survival and neurologic outcomes with hyperoxia. 2, 6
• Stroke patients may experience worse outcomes with excessive oxygen. 2, 5

Practical Approach

Target Oxygen Saturation

• Aim for SpO₂ of 94% to 96% in acute cardiac conditions, as this range is associated with the lowest mortality. 1
• For patients with SpO₂ ≥90%, do not administer routine supplemental oxygen. 1, 4
• For patients with SpO₂ <90%, administer supplemental oxygen to maintain SpO₂ ≥90%. 4

Monitoring Strategy

• Use continuous pulse oximetry for all patients receiving or being considered for oxygen therapy. 4
• Consider arterial blood gas analysis when pulse oximetry may be unreliable or in patients with respiratory distress. 4
• Titrate oxygen to the minimum amount needed to maintain adequate saturation—avoid hyperoxia. 2, 7