Oxygen Therapy During Resuscitation: Why 100% O2 Is Standard & Exceptions

Current ACLS/PALS guidelines recommend 100% oxygen (FiO₂ 1.0) during cardiac arrest and immediate post-ROSC (return of spontaneous circulation) resuscitation.

Rationale for 100% O₂

• Maximizes Oxygen Delivery: Increases alveolar PAO₂ → higher PaO₂ → greater O₂ content (CaO₂ = 1.34 × Hb × SaO₂ + 0.003 × PaO₂).
• Reverses Hypoxemia Rapidly: Critical in arrest where tissue O₂ extraction is maximal and reserves are depleted.
• Simplifies Protocol: One standard concentration eliminates titration delays during crisis.

Important Exceptions

Scenario	Recommended FiO₂	Reason
Known Severe COPD / Chronic Hypercapnic Respiratory Failure	Titrate to SpO₂ 88–92%	High FiO₂ may suppress hypoxic drive → worsening hypercapnia, respiratory acidosis
Neonatal Resuscitation (Term & Preterm)	Start 21% (room air) or 30%; titrate to target SpO₂ by minute	Hyperoxia causes oxidative injury (ROP, BPD, brain); NRP algorithm guides titration
Post-ROSC (after stabilization)	Titrate to SpO₂ 92–98% (94–98% per AHA)	Avoid hyperoxia-associated reperfusion injury & vasoconstriction
Carbon Monoxide Poisoning	100% O₂ (non-rebreather) ± Hyperbaric O₂	Competes with CO for Hb binding; half-life 320 min on RA → 80 min on 100% O₂

Bottom Line: Default to 100% O₂ in arrest. Titrate down once stable, guided by SpO₂, blood gas, and clinical context.