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Nasal Cannulae FiO2 2 L/min — FRCA Primary MCQ

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EasyPhysiology - RespiratoryNasal Cannulae FiO2 2 L/minFRCA Primary

Regarding oxygen therapy a nasal cannula at 2 L/min delivers an approximate FiO2 of:

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Correct answer: A — 0.28

Nasal cannulae deliver approximately 3-4% increase in FiO2 per L/min of O2 flow above room air (21%). At 2 L/min: FiO2 ≈ 0.21 + (2 × 0.03-0.04) ≈ 0.27-0.29 ≈ 0.28. This is approximate because actual FiO2 depends on the patient's respiratory rate / tidal volume / and breathing pattern. Maximum useful flow is 4-6 L/min.

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist