Oxygen Delivery Devices on the NCLEX
Nasal cannula through non-rebreather and high-flow: flow rates, FiO2 ranges, and when each device is the wrong choice.
Every device has a flow range and an FiO2 range. Questions test both, plus the failure mode of each device.
Nasal cannula
1 to 6 L/min, roughly 24% to 44% FiO2 (about 4% per liter). Comfortable, allows eating and talking. Above 4 L/min, humidify; above 6 L/min it just dries and irritates without adding much FiO2. Wrong choice for a mouth-breathing patient in real distress or anyone needing high, reliable FiO2.
Masks
Simple mask: 6 to 10 L/min, about 40% to 60%. Never run it below 5 L/min: exhaled CO2 accumulates in the mask and gets rebreathed. Partial rebreather: 6 to 10 L/min, roughly 60% to 75%; the bag captures some exhaled gas rich in oxygen. Non-rebreather: 10 to 15 L/min, roughly 80% to 95%. One-way valves stop exhaled air from entering the bag. Keep the reservoir bag at least two-thirds inflated; a collapsed bag means the flow is too low and the patient is air-hungry against a closed system. The NRB is the emergency device while you fix the underlying problem or escalate.
Venturi and high-flow
Venturi mask: precise FiO2 from 24% to about 50% via color-coded adapters. The device of choice when exact FiO2 matters, classically COPD with CO2 retention. High-flow nasal cannula: heated, humidified flow up to about 60 L/min with FiO2 titratable from 21% to 100%. Provides some positive pressure and washes out dead-space CO2. Used in hypoxemic respiratory failure; the patient on high-flow who keeps deteriorating is heading toward BiPAP or intubation.
Choosing wrong
COPD retainer on an unmonitored high-FiO2 device: titrate to SpO2 88% to 92%, not 100%. Panicking claustrophobic patient in a mask that keeps coming off: a cannula they wear beats a mask on the pillow. Any device is wrong if the patient is tiring, dropping their rate, or losing their airway: that is ventilation failing, and more oxygen alone will not fix it.
Frequently asked
Reservoir bag collapses on inhalation?
Increase the flow. The bag on a non-rebreather should stay at least two-thirds full through the cycle.
Why never a simple mask at 3 L/min?
Below 5 L/min the mask becomes a CO2 rebreathing chamber. Use a cannula at low flows.
Best device for precise FiO2 in COPD?
Venturi mask. It delivers a fixed FiO2 regardless of breathing pattern.
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