Adult oxygen therapy

Oxygen Delivery Devices: Flow Rates & Estimated FiO2

Compare standard nasal cannula, simple mask, Venturi mask, reservoir masks, OxyMask, Oxymizer, and high-flow nasal cannula—with setup checks and the safety details that are easy to miss.

Adult acute-care focus
Safety boundaries included
Evidence reviewed 2026

Interactive reference

Choose an oxygen device

Review the usual adult acute-care range, how the FiO₂ should be interpreted, setup checks, and the most important safety boundaries.

These are orientation ranges, not patient-specific orders. Use the current device labeling, prescribed target, facility policy, and the patient’s clinical response.

Low-flow

Standard nasal cannula

Also called: Low-flow nasal cannula, Nasal prongs

Oxygen flow

1–6 L/min

Estimated FiO₂

≈24–44%

Comfortable low-flow oxygen delivery when the patient can protect the airway and does not require a controlled FiO₂.

Setup check

  • Place the prongs in the nares with the curve directed downward.
  • Confirm the tubing is connected, flowing, and not kinked.
  • Reassess SpO₂, respiratory effort, comfort, skin, and nares after application.

Safety boundaries

  • The Rule of 4s is only a bedside estimate; actual FiO₂ changes with inspiratory demand, breathing pattern, tidal volume, fit, and room-air entrainment.
  • Do not extrapolate the Rule of 4s above the labeled range of a standard cannula.
  • Consider humidification for comfort when flow exceeds 4 L/min, consistent with local policy.

Sources for this device

AARCNCBI BookshelfEuropean Respiratory Society

Nasal cannula shortcut

The Rule of 4s

For a standard low-flow nasal cannula, begin with approximately 20% and add four percentage points for every 1 L/min of oxygen.

Estimated FiO₂ ≈ 20% + (4 × flow in L/min)

1 L/min

≈24%

2 L/min

≈28%

3 L/min

≈32%

4 L/min

≈36%

5 L/min

≈40%

6 L/min

≈44%

This estimates device output, not the oxygen concentration reaching the alveoli. Actual delivery varies with respiratory rate, tidal volume, inspiratory flow demand, breathing pattern, mouth breathing, cannula position, and room-air entrainment.

Source: NCBI Nursing Skills — Oxygen Therapy

When humidification may help

For adults receiving conventional oxygen above 4 L/min, humidification may be considered to improve comfort and adherence—particularly when higher-flow oxygen will be used for a prolonged period. Use a humidifier compatible with the oxygen source, flow, interface, and facility policy.

Source: AARC adult acute-care oxygen guideline

Bubble humidifier flow warning

Never assume a basic unheated bubble humidifier can accept the full output of a 15 L/min flowmeter.

Check the exact bottle’s labeled range. For example, AirLife lists its standard 7100 bottle for 2–6 L/min and the 7600 for 3–7 L/min; operating outside the recommended range may affect safety pop-off function. Its separate 7900 high-flow bottle is designed for 6–15 L/min. If the pressure-relief valve sounds, check immediately for kinked or blocked tubing and follow the manufacturer instructions—do not silence or bypass it.

Standard bottle guide High-flow bottle specifications

Extension tubing at higher flows

Use oxygen tubing, connectors, and a patient interface specifically rated for the intended flow and source. Do not assume that any long extension can safely carry a high flow.

  • Use the shortest practical run, minimize added connectors, and check the entire line for kinks, compression, loose connections, leaks, and collected water.
  • Longer or narrow tubing and extra connectors can add resistance and back pressure. Reassess oxygen delivery and the patient after changing the circuit.
  • Match every component: a high-flow-rated cannula does not make a standard bubble humidifier or unverified extension tubing high-flow capable.
  • Do not add ordinary oxygen extension tubing to a heated HFNC circuit unless the HFNC manufacturer explicitly permits that configuration.

Manufacturer example: AirLife offers model-specific high-flow cannulas rated up to 15 L/min, including a 50-foot configuration, and separately offers crush-resistant oxygen supply tubing in multiple lengths. This illustrates why the exact product combination—not a universal length rule—must determine suitability.

High-flow cannula specifications Oxygen supply tubing specifications

At-a-glance comparison

Oxygen device flow and FiO₂ chart

Approximate values describe a usual orientation range—not a guaranteed patient dose. Product-specific devices must be used according to their current labeling.

DeviceClassificationFlowFiO₂Interpretation
Standard nasal cannulaLow-flow1–6 L/min≈24–44%Estimated
Simple face maskLow-flow5–10 L/min≈35–60%Estimated
Venturi maskAir-entrainmentAdapter-specificCommonly 24–50%Controlled
Partial rebreather maskReservoirProduct-specific; commonly 6–10 L/minApproximate; commonly 40–70%Product-specific
Non-rebreather maskReservoirCommonly 10–15 L/min≈60–80% or higher, depending on system performanceEstimated
OxyMaskOpen maskModel-specific; current Medline page lists 1–15 L/minModel-specific; current Medline page lists 24–90%Product-specific
Oxymizer reservoir cannulaReservoirModel-specific; some current products list use up to 15 L/minNot reliably assigned by the standard cannula Rule of 4sProduct-specific
High-flow nasal cannulaHigh-flowSystem-specific; AIRVO 2 lists 2–60 L/minSet independently; commonly 21–100%Set independently

Variable performance

Low-flow oxygen devices

A low-flow device does not meet the patient’s entire inspiratory flow demand. Supplemental oxygen mixes with entrained room air, so the actual inspired concentration varies with respiratory rate, tidal volume, inspiratory demand, fit, and breathing pattern.

Different operating principle

Controlled and high-flow systems

Air-entrainment systems can provide a more controlled FiO₂ when configured exactly as labeled and when total flow meets inspiratory demand. Heated HFNC uses an active system in which flow and FiO₂ are set separately. Neither should be treated like a standard cannula flow chart.

Common questions

Oxygen-device FAQ

What is the nasal cannula Rule of 4s?

The Rule of 4s estimates standard nasal-cannula FiO₂ by starting near 20% and adding approximately four percentage points for each liter per minute. This gives about 24% at 1 L/min through 44% at 6 L/min. Actual delivery varies with the patient and room-air entrainment.

What is the minimum flow for a simple oxygen mask?

A conventional simple face mask should not be operated below 5 L/min because inadequate flow may permit rebreathing of exhaled carbon dioxide. Some products and facility policies specify a 6 L/min minimum, so current labeling and local policy should be followed.

Does a nasal cannula deliver an exact FiO₂?

No. A standard nasal cannula is a low-flow, variable-performance device. Respiratory rate, tidal volume, inspiratory flow demand, breathing pattern, fit, mouth breathing, and room-air entrainment affect the oxygen concentration actually inspired.

What flow should be used with a Venturi mask?

Use the oxygen flow printed on the exact Venturi adapter or stated in its current manufacturer instructions. Adapter colors, available concentrations, and required source flows are not universal across products.

Does a non-rebreather mask provide 100% oxygen?

A non-rebreather mask does not guarantee 100% inspired oxygen. Mask seal, valve function, reservoir inflation, source flow, and the patient’s inspiratory demand influence delivery. The reservoir should be inflated before use and should not substantially collapse during inspiration.

Can a standard bubble humidifier be used at 15 L/min?

Not unless that exact humidifier is labeled for the flow. As one manufacturer example, AirLife lists standard 7100 and 7600 bubble humidifiers only through 6 and 7 L/min, respectively, while its separate 7900 high-flow model is designed for 6 to 15 L/min. Operating outside the labeled range may affect safety pop-off function.

Can oxygen extension tubing be used at higher flow rates?

Only when the oxygen source, tubing, connectors, humidifier, and patient interface are compatible with the intended flow and configuration. Longer or narrow tubing and added connectors can increase resistance and back pressure. Use manufacturer-approved components, inspect the complete line, and reassess delivery after changing the circuit.

Evidence base

Clinical and manufacturer sources

Sources and links reviewed September 2, 2026. Manufacturer specifications can change and may differ between models or markets. PulmTools is independent and does not claim endorsement by the organizations or manufacturers listed.

AARC — Management of Adult Patients With Oxygen in the Acute Care Setting (2022)Clinical practice guideline covering oxygen targets, monitoring, humidification, and high-flow nasal cannula in adult acute care.NCBI Bookshelf — Nursing Skills: Oxygen TherapyOpen nursing reference describing common interfaces, typical flow ranges, estimated FiO₂, setup, and device safety checks.European Respiratory Society — Oxygen devices and delivery systemsPeer-reviewed clinical review of conventional cannulas, masks, reservoir systems, Venturi devices, and high-flow therapy.Medline — OxyMask product informationCurrent manufacturer/distributor specifications for the open OxyMask product family. Verify the stocked model and its instructions for use.Medline — U/Connect-It Venturi mask product noticeManufacturer material documenting available adapter concentrations; the selected product labeling determines the required oxygen flow.Drive DeVilbiss — Oxymizer product informationCurrent reservoir-cannula product information. Availability and labeling may differ by market and exact model.Fisher & Paykel Healthcare — AIRVO 2 systemManufacturer specifications for a heated, humidified high-flow system, including its integrated flow range and compatible interfaces.AirLife — Standard Bubble Humidifier specifications and hospital user guideManufacturer specifications list the 7100 at 2–6 L/min and the 7600 at 3–7 L/min. The user guide warns that operating outside the recommended range may affect safety pop-off function.Drive Medical / Salter Labs — High-Flow Bubble HumidifierManufacturer specifications for the separate 7900 high-flow bottle list a 6–15 L/min operating range and a 6 PSI safety pop-off valve.AirLife — 3-Channel Oxygen Supply TubingManufacturer product information for crush-resistant oxygen supply tubing and available lengths. Tubing length alone does not establish compatibility with every oxygen source or interface.AirLife — Salter-Style High-Flow Oxygen CannulaManufacturer specifications identify model-specific high-flow cannulas, including configurations rated up to 15 L/min and supplied in lengths up to 50 feet.

Clinical scope and limitations

This adult educational reference does not select a device for an individual patient and does not replace an oxygen order, bedside assessment, manufacturer instructions, respiratory therapy consultation, or facility protocol. Pediatric and neonatal oxygen delivery require population-specific guidance.

Oxygen saturation targets

Match the clinical context to source-labeled SpO₂ guidance.

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Oxygen tank duration

Estimate remaining cylinder time from pressure, flow, and reserve.

Open tool

ROX index

Review HFNC response using SpO₂, FiO₂, and respiratory rate.

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