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HLT-RESP80-04 · Lesson 3 · 40 clock hours · lab

Low-Flow Oxygen Delivery Devices

Objective. The student will set up and apply nasal cannula, simple mask, partial re-breather mask, and non-re-breather mask on a manikin, selecting the correct flow rate to achieve a specified FiO2 range for each device.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Low-Flow Oxygen Delivery Devices

Low-flow oxygen delivery systems supply supplemental oxygen at flow rates that do not meet the patient's entire inspiratory demand. Room air is entrained around the device and mixes with the delivered oxygen, so the fraction of inspired oxygen (FiO₂) that actually reaches the lungs varies with the patient's breathing pattern, tidal volume, and respiratory rate. Understanding each device—its construction, appropriate flow range, and expected FiO₂—is a core clinical skill and a topic tested on both the NBRC CRT and RRT examinations.

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Nasal Cannula

The nasal cannula (NC) consists of two short prongs that sit just inside the nares, connected to oxygen supply tubing. It is the most commonly used oxygen device because it is comfortable, inexpensive, and allows the patient to eat, speak, and expectorate without interruption.

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Simple Mask

The simple mask (also called a simple face mask) is a soft plastic mask that fits over the nose and mouth. It has side exhalation ports and no reservoir bag. The small volume inside the mask itself acts as a minor reservoir.

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Partial Re-Breather Mask

The partial re-breather mask (PRM) adds a reservoir bag to the simple mask. On inhalation, the patient draws oxygen from both the flowmeter and the reservoir bag. The first portion of exhaled gas (from anatomic dead space, which is rich in oxygen and low in CO₂) refills the bag; later exhaled gas exits through the side ports.

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Non-Re-Breather Mask

The non-re-breather mask (NRB) is similar in appearance to the PRM but includes one-way valves: a valve between the bag and the mask (prevents exhaled gas from entering the bag) and valves over one or both exhalation ports (prevents room air entrainment). This design delivers the highest FiO₂ of any low-flow device.

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FiO₂ Reference Summary

| Device | Flow Range (L/min) | Approx. FiO₂ |

|---|---|---|

| Nasal Cannula | 1–6 | 0.24–0.44 |

| Simple Mask | 5–10 | 0.35–0.50 |

| Partial Re-Breather | 6–10 | 0.40–0.70 |

| Non-Re-Breather | 10–15 | 0.60–0.80 |

Remember: all FiO₂ values are estimates. Actual delivered FiO₂ varies with the patient's breathing pattern.

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General Safety Principles

1. Verify the flow rate against the ordered FiO₂ or SpO₂ target before applying any device.

2. Check all connections and tubing for kinks, cracks, or disconnections before and during use.

3. Assess the patient continuously — SpO₂, work of breathing, and mental status should guide adjustments.

4. Humidification is recommended at flows above 4 L/min via nasal cannula and is good practice with any mask worn for extended periods.

5. Oxygen is a medication — apply only what is ordered or required by the clinical situation; excessive oxygen can be harmful in certain patient populations (e.g., those with chronic hypercapnia).

6. Document device, flow rate, patient response, and time of application in the medical record.

Key terms10

FiO₂ (Fraction of Inspired Oxygen)The proportion of oxygen in the gas mixture a patient breathes, expressed as a decimal (e.g., 0.21 for room air, 1.0 for 100% oxygen).
Low-flow oxygen systemAn oxygen delivery system that supplies flow rates insufficient to meet the patient's full inspiratory demand; room air is entrained and mixed with delivered oxygen, making FiO₂ variable.
Nasal cannulaA low-flow device with two short prongs inserted into the nares; delivers approximately 0.24–0.44 FiO₂ at 1–6 L/min.
Simple maskA low-flow face mask without a reservoir bag; delivers approximately 0.35–0.50 FiO₂ at 5–10 L/min; minimum 5 L/min required to flush CO₂.
Reservoir bagA collapsible bag attached to a re-breather or non-re-breather mask that stores oxygen between breaths, allowing a higher FiO₂ than masks without one.
Partial re-breather maskA mask with a reservoir bag but no one-way valves; the initial portion of exhaled dead-space gas (oxygen-rich) refills the bag; delivers approximately 0.40–0.70 FiO₂ at 6–10 L/min.
Non-re-breather maskA mask with a reservoir bag and one-way valves that prevent exhaled gas from re-entering the bag and limit room air entrainment; delivers approximately 0.60–0.80 FiO₂ at 10–15 L/min.
Bubble humidifierA small water reservoir attached inline to the oxygen flowmeter that adds moisture to the delivered gas, recommended at flows above 4 L/min to prevent mucosal dryness.
Air entrainmentThe mixing of room air (21% oxygen) into the delivered oxygen stream, which dilutes the FiO₂; inherent in all low-flow systems.
One-way valveA flap or disc valve on a non-re-breather mask that controls the direction of gas flow, preventing exhaled gas from entering the reservoir bag and reducing room air inhalation.

Worked examples4

1. A physician orders oxygen via nasal cannula at 3 L/min. What is the estimated FiO₂ the patient will receive?
  1. Room air baseline FiO₂ = 0.21.
  2. Each 1 L/min of nasal cannula flow adds approximately 0.04 to the FiO₂ above room air.
  3. Calculate: 0.21 + (3 L/min × 0.04) = 0.21 + 0.12 = 0.33.
Answer: The estimated FiO₂ at 3 L/min via nasal cannula is approximately 0.33 (33%).
2. You need to deliver an estimated FiO₂ of 0.44 via nasal cannula. What flow rate should you set?
  1. Target FiO₂ = 0.44; room air FiO₂ = 0.21.
  2. Additional FiO₂ needed above room air: 0.44 − 0.21 = 0.23.
  3. Each L/min adds 0.04: flow rate = 0.23 ÷ 0.04 = 5.75 L/min.
  4. Round to the nearest whole liter: 6 L/min (the maximum recommended for nasal cannula), which yields approximately 0.44 FiO₂.
Answer: Set the nasal cannula at 6 L/min to achieve approximately 0.44 FiO₂.
3. A patient is placed on a simple mask running at 4 L/min. Is this safe? What action should you take?
  1. The minimum safe flow for a simple mask is 5 L/min.
  2. At 4 L/min, exhaled CO₂ will not be adequately flushed from the mask body, creating a rebreathing hazard.
  3. Immediately increase the flow to at least 5 L/min.
  4. Reassess the patient and document the change.
Answer: A flow of 4 L/min on a simple mask is unsafe. Increase to a minimum of 5 L/min to prevent CO₂ rebreathing.
4. You are setting up a non-re-breather mask at 12 L/min. During your check, the reservoir bag collapses completely when the patient inhales. What does this indicate and how do you correct it?
  1. A fully collapsing reservoir bag indicates the oxygen flow is insufficient to maintain bag volume against the patient's inspiratory demand.
  2. Verify the tubing is not kinked and all connections are secure.
  3. If tubing is intact, increase the flow rate in 1–2 L/min increments until the bag remains at least one-third to one-half inflated during inhalation.
  4. Do not exceed the device's recommended maximum flow (typically 15 L/min); if the bag still collapses, assess for a mask-seal leak or switch to a higher-level oxygen system and notify the physician.
Answer: A collapsing reservoir bag signals inadequate flow or a leak. Increase flow (up to 15 L/min maximum) until the bag stays adequately inflated; check for leaks; escalate care if the problem persists.

The math in this lesson1

Learners estimate FiO₂ as 0.21 plus 0.04 per L/min of nasal cannula flow.
F-LE.1
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstration of each device with side-by-side FiO2 range table review; students annotate a blank table from memory and compare with reference. · Paired practice: each student sets up and applies all four devices on a head-form manikin while verbally stating the flow rate and expected FiO2 range; partner uses a checklist to evaluate technique. · Troubleshooting drill: instructor pre-sets six common problems (displaced cannula prong, collapsed reservoir bag, kinked tubing, incorrect flow, missing humidifier water, cracked mask seal) and students identify and correct each within a timed station rotation.
Materials: Adult head-form manikins, nasal cannulas (adult and pediatric), simple masks, partial re-breather masks, non-re-breather masks, bubble humidifiers, flowmeters, FiO2 reference table, troubleshooting checklist, stopwatch
Check: Skills checklist scored by instructor; student must pass all critical steps (correct flow rate, proper fit, reservoir bag inflated on NRB) and achieve 80% overall; troubleshooting drill: 5 of 6 problems identified and corrected correctly.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Equipment and Device Management
1. A nasal cannula is running at 2 L/min. What is the estimated FiO₂ delivered to the patient?
Patient Safety and Equipment Management
2. What is the minimum acceptable oxygen flow rate for a simple face mask, and why?
Equipment and Device Management
3. Which feature distinguishes a non-re-breather mask from a partial re-breather mask?
Troubleshooting and Patient Safety
4. A patient wearing a non-re-breather mask at 12 L/min has a reservoir bag that deflates completely with each breath. Which action should the respiratory therapist take first?
Clinical Decision Making
5. Which of the following patients is the BEST candidate for a simple mask rather than a nasal cannula?
Patient Safety and Equipment Management
6. During a troubleshooting drill, a student finds that the bubble humidifier attached to a nasal cannula at 5 L/min contains no water. What is the primary clinical concern?
Equipment and Device Management
7. A respiratory therapist applies a partial re-breather mask at 8 L/min. Which assessment finding confirms proper setup?
Clinical Decision Making
8. A therapist is asked to deliver the highest possible FiO₂ via a low-flow device to a patient with severe hypoxemia. Which device and flow rate is most appropriate?
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