High-flow nasal cannula (HFNC) oxygen therapy generates a small but clinically significant positive nasopharyngeal pressure. At a flow rate of 60 L/min, approximately what positive end-expiratory pressure equivalent does it generate in adults?
- A 0.5–1 cmH2O
- B 8–10 cmH2O
- C 2–5 cmH2O ✓
- D 12–15 cmH2O
Correct answer: C. 2–5 cmH2O
Explanation
HFNC at flows of 40–60 L/min generates approximately 2–5 cmH2O of nasopharyngeal pressure with mouth closed (mouth open reduces this significantly). This provides modest CPAP-like effects — alveolar recruitment, reduced dead space washout, and improved FRC — contributing to improved oxygenation beyond FiO2 enrichment alone. HFNC delivers FiO2 close to 1.0 at high flows, washes out nasopharyngeal dead space, and reduces work of breathing. It is used for pre-oxygenation in difficult airway management and as a bridge during extubation in high-risk patients.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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