High-flow nasal oxygen (HFNO) therapy is increasingly used as a pre-oxygenation technique before intubation. It maintains apnoeic oxygenation during the intubation attempt primarily because:

• A The high flow rate generates sufficient PEEP to maintain alveolar recruitment during apnoea
• B High flow creates turbulent gas mixing that improves CO2 clearance, preventing hypercapnia
• C Oxygen delivered via nasopharynx washes out airway dead space, creating an apnoeic oxygenation reservoir extending safe apnoea time ✓
• D Humidification prevents mucociliary dysfunction, maintaining airway patency during the intubation attempt

Explanation

Apnoeic oxygenation relies on the fact that, even without ventilation, oxygen continues to diffuse from the alveolar reservoir into pulmonary blood because O2 is consumed (250 mL/min) faster than CO2 is produced (200 mL/min). This creates a bulk flow of gas from the nasopharynx towards the alveoli (mass movement). HFNO at 40–70 L/min washes out nitrogen from the nasopharyngeal dead space, fills this reservoir with pure oxygen, and sustains the bulk flow mechanism. Studies show HFNO extends safe apnoea time to >10 minutes in healthy patients. While modest PEEP (2–3 cmH2O) is generated, this is not the primary mechanism of oxygenation benefit.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.