Nursing care
Nasal cannula vs non-rebreather mask: flow, oxygen delivered and when to step up
Written and reviewed by Rachel Goldberg, MSN, RN, CEN · 4 min read · Updated November 2026
Short answer
Nasal cannula vs non-rebreather is low oxygen versus high oxygen. A nasal cannula runs at 1 to 6 L/min and gives an FiO2 under about 40 percent, suited to stable clients with mild needs. A non-rebreather mask runs at 10 L/min or more with a reservoir bag and can deliver up to about 80 to 90 percent, for clients who are acutely hypoxic.
The deciding difference: how much oxygen reaches the lungs
MSD Manuals states that a nasal cannula uses 1 to 6 L/min and can give an FiO2 below 40 percent, and that flows above 6 L/min add nothing because that rate already fills the nasopharynx. Open Critical Care gives a similar range, roughly 21 to 45 percent, rising about 2 to 4 percent per liter depending on how the person breathes.
A non-rebreather mask adds a reservoir bag and one-way valves. The client inhales oxygen from the bag, and exhaled air is vented out through a flap rather than breathed back. MSD Manuals notes that leaks around the mask limit the real FiO2 to at most 80 to 90 percent, and Open Critical Care lists a flow of 10 to 20 L/min.
Where the two overlap, and what neither one does
Both are simple devices for a client who is breathing on their own. Neither supports the work of breathing or adds airway pressure, which Open Critical Care lists as a limitation of the non-rebreather. A tiring client with rising carbon dioxide needs more than a bigger oxygen device, and the nurse escalates to the provider rather than only increasing the flow.
Both also deliver a variable FiO2 that changes with the client's breathing pattern. A fast, deep breather pulls in more room air around either device, so the number on the flowmeter is an estimate, not a guarantee. Pulse oximetry and the clinical picture tell the nurse whether the device is working.
The reservoir bag rule students forget
The bag on a non-rebreather has to be filled before the mask goes on and must stay at least partly inflated as the client breathes. Open Critical Care warns that if the flow is too low to keep the reservoir full, the client may receive far less oxygen than planned, which it describes as a suffocation risk. A collapsing bag on inspiration is a finding to fix immediately by raising the flow.
This is why a non-rebreather is never run at cannula-level flows. Setting a non-rebreather at 4 L/min, an error in hurried care, leaves the client breathing against a mask with too little gas behind it. The device that looks like the bigger intervention then performs worse than the cannula it replaced.
When the nurse steps up, and when to step back down
The usual signal to step up is falling oxygen saturation or worsening distress despite a cannula at its upper flow. Restlessness, rising respiratory rate and use of accessory muscles all count. The nurse applies the higher device per protocol or standing order, notifies the provider, and stays to watch the response rather than leaving after the switch.
Stepping down matters as much. MSD Manuals advises giving the lowest FiO2 that achieves acceptable oxygenation, and notes that an FiO2 above 60 percent is best avoided for long periods. Once the client stabilizes, the order is usually weaned back toward a cannula. Clients with COPD need closer watching on high oxygen, as the linked page on oxygen and carbon dioxide explains.
Hypothetical practice scenario
Hypothetical scenario, not a real exam item: a client with pneumonia on a nasal cannula at 6 L/min has a saturation that has fallen from 93 to 86 percent, with a respiratory rate of 30. Which action is best: raise the cannula to 10 L/min, apply a non-rebreather at an adequate flow with the bag filled, or recheck in 30 minutes?
Applying the non-rebreather with the bag filled, then notifying the provider, is best. Raising a standard cannula above 6 L/min adds no benefit, according to MSD Manuals, so it only looks like action while the client stays hypoxic. Waiting 30 minutes leaves an acutely hypoxic client without help.
Sources and further reading
MSD Manual Professional Version: Hypoxia in Hospitalized Patients. Nasal cannula flow of 1 to 6 L/min with FiO2 under 40 percent and no benefit above 6 L/min, non-rebreather FiO2 at most 80 to 90 percent, high-flow nasal cannula 20 to 60 L/min, lowest effective FiO2, avoiding FiO2 above 60 percent, ventilation when oxygen fails.
Open Critical Care: Overview of Oxygen Delivery Devices. Nasal cannula flow and FiO2 range, non-rebreather flow 10 to 20 L/min and FiO2 range, reservoir must stay inflated or FiO2 drops, no support for work of breathing.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our respiratory practice questions are the closest set to what this page covers.
Common questions
What is the max flow for a nasal cannula?
A standard nasal cannula runs at about 1 to 6 L/min. MSD Manuals notes that flows above 6 L/min offer no added benefit. High-flow nasal cannula is a different, humidified system that runs at 20 to 60 L/min.
What FiO2 does a non-rebreather give?
Leaks around the mask mean a non-rebreather delivers an FiO2 of at most about 80 to 90 percent, according to MSD Manuals, even though the reservoir holds pure oxygen. Open Critical Care gives a practical range of about 40 to 85 percent depending on breathing.
When should a nurse switch to a non-rebreather?
When a client on a nasal cannula at its upper flow still has falling oxygen saturation or worsening distress, following protocol or orders. The provider is notified, the bag is filled before the mask goes on, and the client is reassessed right away.