Prolonged exposure to oxygen at which inspired concentration is generally accepted to carry a significant risk of pulmonary oxygen toxicity?
- A FiO2 above 0.60 for more than 24 to 48 hours ✓
- B FiO2 above 0.30 for more than 48 hours
- C FiO2 above 0.40 for more than 1 week
- D FiO2 of 1.0 for less than 6 hours
Correct answer: A. FiO2 above 0.60 for more than 24 to 48 hours
Explanation
Pulmonary oxygen toxicity becomes a real concern when patients breathe an FiO2 above approximately 0.60 for longer than 24 to 48 hours, producing tracheobronchial irritation, absorption atelectasis and later diffuse alveolar damage. Concentrations up to 0.4 are considered safe indefinitely at sea level. Brief exposure to FiO2 1.0 during induction and intubation is routine and harmless, which eliminates option D.
Reference: Morgan and Mikhail's Clinical Anesthesiology, 7th ed.
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