Oxygen Delivery Devices on the NCLEX: Nasal Cannula to Non-Rebreather

Oxygen device questions get easy once you sort them two ways. First, is the device low-flow (the nasal cannula and the masks, where the oxygen the client actually breathes drifts with how fast and deep they breathe) or high-flow (the Venturi mask, which locks a fixed oxygen percentage no matter the breathing pattern)? Second, where does it sit on the escalation ladder from a comfortable nasal cannula up to a non-rebreather for an emergency? Learn the flow rate, the rough oxygen percentage, and the one nursing point for each of the five devices, and this whole topic turns into fast points.

Low-flow vs high-flow: the split that organizes everything

A low-flow device delivers oxygen at a set liter flow, but the client also pulls in room air around it. So the oxygen they truly breathe (the FiO2, the fraction of inspired oxygen) rises and falls with their rate and depth. A fast, shallow breather dilutes the oxygen with more room air; a slow, deep breather gets a higher concentration. The nasal cannula, simple mask, partial rebreather, and non-rebreather are all low-flow, which is why their oxygen percentages are given as ranges, not exact numbers.

A high-flow device meets or exceeds the client's entire inspired volume, so almost no room air sneaks in and the FiO2 stays fixed. The Venturi mask is the classic high-flow device on the exam: you dial an exact percentage and it holds it. That precision is why it is the go-to for a client with COPD, where the oxygen has to be titrated carefully. When a stem says the oxygen level must stay exactly the same regardless of breathing, it is pointing at the Venturi mask.

The devices also form an escalation ladder. Start low and comfortable, then step up as the client needs more: nasal cannula, then a simple mask, then a non-rebreather for the highest dose short of a breathing tube. Practice the calls below, then read on for the flow rates and the traps.

The five devices at a glance

Keep this table as your quick reference. The percentages are approximate for the low-flow devices (they vary a few points by source and by the client's breathing), but the flow rates and the signature nursing point for each are what the exam tests.

Nasal cannula: the comfortable low-flow workhorse

The nasal cannula runs at 1 to 6 L/min and delivers roughly 24 to 44% oxygen. It is the most comfortable device and the only one a client can keep on while eating, drinking, and talking, so it is the default for someone who is stable and needs only a modest boost. The trade-off is that it is low-flow, so the exact oxygen depends on the client's breathing, and it tops out around 6 L/min.

The tested safety point is humidification. Above 4 L/min, the fast, dry gas irritates and dries the nasal passages, so warm humidification is added to prevent cracking, discomfort, and nosebleeds. Cranking a cannula past 6 L/min does not meaningfully raise the oxygen and just dries the nose more, so the correct move when a client needs more is to step up to a mask, not to keep turning up the cannula.

The masks: simple, partial rebreather, and non-rebreather

The simple face mask covers the nose and mouth and runs at about 6 to 10 L/min for roughly 35 to 50% oxygen, filling the gap above the cannula. Its one hard rule: never run it below about 5 L/min. At a low flow the client's own exhaled carbon dioxide collects inside the mask and gets rebreathed, so a minimum flow is needed to flush it out.

The next two masks add a reservoir bag that fills with oxygen between breaths, so the client inhales a richer mix. The difference between them is the one-way valves. A partial rebreather (about 10 to 12 L/min, roughly 60 to 75%) has no valves, so the first part of each exhalation flows back into the bag. A non-rebreather (10 to 15 L/min, roughly 80 to 95%) adds one-way valves that block exhaled air from entering the bag and block room air from leaking in, so it delivers the highest oxygen of any mask without an advanced airway. It is the device for an unstable, badly hypoxic client, the same client you learned to catch on the deteriorating-patient post.

Venturi mask: when the percentage must be exact

The Venturi mask is the high-flow, fixed-performance device. Color-coded adaptors set a precise oxygen percentage (commonly 24, 28, 31, 35, 40, and 50%), and each adaptor tells you the flow rate to set. Because it holds that percentage no matter how the client breathes, it is the most reliable and precise device and the classic answer for a client with COPD, whose oxygen must be titrated carefully. This ties straight into your ABG and respiratory work.

The COPD logic the exam wants: give the lowest effective oxygen and titrate to the ordered target saturation (for many COPD clients that target runs around 88 to 92%, lower than the usual goal). The concern is that too much oxygen can worsen carbon dioxide retention. But note the flip side the exam also tests: you never withhold oxygen from a hypoxic client. A client who is truly short of oxygen gets it; the skill is titrating carefully, and the Venturi mask is what lets you do that precisely.

How to escalate when the oxygen is not enough

When a client's saturation stays low, follow the ladder rather than simply maxing out whatever device is on. A rough order for a spontaneously breathing client:

1. Nasal cannula for a stable client needing a small boost (titrate 1 to 6 L/min; humidify above 4).
2. Simple face mask for a mid-range need (about 6 to 10 L/min, 35 to 50%).
3. Non-rebreather for an emergency, when you need the highest oxygen fast (10 to 15 L/min, up to about 95%); this is the bridge while you escalate care.
4. Venturi mask whenever the oxygen must be an exact, controlled percentage, especially in COPD, at any point on the ladder.

Alongside the device, always do the nursing basics: reassess the oxygen saturation and work of breathing, sit the client upright to ease breathing, and stay with a client who needed a rapid step up. The device delivers the oxygen; your assessment tells you whether it is working.

• Low-flow drifts, high-flow is fixed. The cannula and the masks are low-flow, so their oxygen percentage varies with breathing. The Venturi mask is high-flow and holds an exact percentage.
• Nasal cannula: 1 to 6 L/min, about 24 to 44%. Start at 24% for 1 L/min and add about 4% per liter. Humidify above 4 L/min, and step up to a mask instead of pushing past 6 L/min.
• Simple mask needs at least about 5 L/min. About 6 to 10 L/min for 35 to 50%. Below roughly 5 L/min, the client rebreathes exhaled carbon dioxide.
• Valves separate partial from non-rebreather. Both have a reservoir bag. The non-rebreather adds one-way valves and delivers the most oxygen (about 80 to 95%); keep the bag inflated on either one.
• Venturi mask is the COPD precision device. Color-coded adaptors set an exact 24 to 50%. Give the lowest effective oxygen and titrate to the ordered target, but never withhold oxygen from a hypoxic client.