Oxygen Delivery Systems: Clinical Selection and Troubleshooting

Oxygen Delivery Systems: Clinical Selection and Troubleshooting

Selecting the right oxygen delivery device is one of the most fundamental clinical decisions a respiratory therapist makes. The wrong choice can leave a patient hypoxic, cause carbon dioxide retention in a patient at risk, or deliver far more oxygen than is needed. This lesson covers the six core devices you will use in clinical practice, how to set them up safely, and how to recognize and correct common equipment failures.

The Six Core Devices

Nasal cannula (NC) delivers low-flow oxygen through two soft prongs seated just inside the nostrils. Flow rates typically range from 1–6 L/min, producing an estimated FiO₂ of roughly 0.24–0.44, though the actual FiO₂ varies with the patient's breathing pattern. It is comfortable, allows eating and talking, and is appropriate for patients who need mild supplemental oxygen and can breathe through their nose. Humidification is generally recommended when flow exceeds 4 L/min to prevent mucosal dryness.

Simple mask covers the nose and mouth and contains small side exhalation ports. Flow must be maintained at a minimum of 5 L/min to flush exhaled CO₂ from the mask; flows of 5–10 L/min deliver an estimated FiO₂ of roughly 0.35–0.55. Never run a simple mask below 5 L/min — CO₂ can accumulate inside the mask.

Partial rebreather mask adds a reservoir bag to the simple mask. A portion of the patient's exhaled air — primarily from early exhalation (dead-space gas, which is rich in oxygen and low in CO₂) — refills the bag. Flow must be set high enough that the reservoir bag does not fully collapse on inspiration; typical flows are 6–10 L/min, yielding an estimated FiO₂ up to approximately 0.60.

Non-rebreather mask (NRB) also has a reservoir bag but adds one-way valves: a valve between the bag and mask prevents exhaled gas from entering the bag, and valves over the exhalation ports prevent room air from being inhaled. This produces the highest FiO₂ available from a low-flow system — up to approximately 0.60–0.80 at 10–15 L/min. The bag must remain at least one-third to one-half inflated at all times. If the bag collapses completely, the patient cannot inhale adequate gas — this is a critical malfunction requiring immediate correction.

Venturi mask (air-entrainment mask) is the device of choice when a precise, consistent FiO₂ is required — most importantly in patients at risk for hypercapnic respiratory failure (for example, certain patients with COPD). Color-coded adapters entrain a fixed ratio of room air, producing a specific FiO₂ regardless of the patient's breathing pattern. Common settings range from 0.24 to 0.50. Always confirm the correct color-coded adapter is in place and set the flow rate printed on that adapter.

High-flow nasal cannula (HFNC) delivers heated, humidified oxygen at flows up to 60 L/min, meeting or exceeding the patient's peak inspiratory demand. This allows a more reliable and adjustable FiO₂ (0.21–1.0) and provides a small amount of positive airway pressure. HFNC requires a dedicated blender and heated humidifier system. It is used for moderate-to-severe hypoxemia and patients who need high FiO₂ but are not intubated.

Selecting the Right Device

Ask three questions for every patient:

1. What FiO₂ is needed? Target SpO₂ guides this decision, along with the physician's order and clinical context.

2. Does the patient have hypercapnic risk? If yes, use a Venturi mask to prevent over-oxygenation and unintended suppression of hypoxic drive in susceptible patients.

3. Can the patient cooperate and tolerate the device? An agitated or confused patient may not tolerate a tight-fitting mask; a cannula may be safer even if flow requirements are higher.

Setup and Verification

For every device: (1) confirm the order, (2) assemble all components, (3) connect to a calibrated flow meter, (4) set the prescribed flow rate, (5) check for leaks and proper connections, (6) verify humidification is functioning when required, and (7) apply the device to the patient and reassess SpO₂ within a clinically appropriate interval.

Troubleshooting

| Malfunction | Signs | Corrective Action |

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

| Disconnected tubing | No flow; patient not improving; audible hiss at connection point | Reconnect securely; verify flow resumes |

| Incorrect flow rate | SpO₂ not at target; flow meter ball not at prescribed mark | Adjust flow meter to ordered rate |

| Depleted humidifier water | Gurgling stops; patient reports dryness; water chamber empty | Refill or replace bubble humidifier per facility policy |

| NRB bag not inflating | Bag remains flat or collapses on inhalation | Check that flow is adequate; verify one-way valve is seated correctly; check for leaks at mask seal |

Safety Points

• Never run a simple mask below 5 L/min.
• Always pre-inflate the NRB reservoir bag before placing on the patient.
• Verify the Venturi adapter color and printed flow setting match the order.
• Assess the patient — not just the equipment — after every change. SpO₂, respiratory rate, work of breathing, and mental status all matter.
• Oxygen supports combustion: keep sources away from open flames and notify staff of oxygen in use.
• Know your scope: if a device change does not improve the patient's condition, escalate to the supervising clinician promptly.