Respiratory Oxygen Delivery Methods

Low-Flow Oxygen Delivery Systems

• The British Thoracic Society recommends nasal cannula for medium-concentration oxygen therapy, delivering oxygen flow rates of 1-6 L/min, providing approximately 24-50% FiO2 1, 2
• Nasal cannula has advantages, including greater patient comfort, can be worn during meals and speech, and is less likely to be removed by patients, with lower inspiratory resistance than face masks and no risk of carbon dioxide rebreathing 1, 3
• The American Thoracic Society suggests that nasal cannula flow rates should be adjusted based on oximetry measurements and blood gas results, with a preference for medium-concentration oxygen therapy over simple face masks 1
• High-flow nasal cannula (HFNC) delivers warmed, humidified oxygen at flow rates of 30-70 L/min, providing more predictable FiO2 and modest positive airway pressure (CPAP effect), and is recommended for acute hypoxemic respiratory failure and post-extubation respiratory support 4, 5

Mask Oxygen Delivery Systems

• Simple face masks deliver 40-60% FiO2 at flow rates of 5-10 L/min, but should never be used at flow rates below 5 L/min due to risk of CO2 rebreathing, and are less preferred than nasal cannula for medium-concentration oxygen therapy due to patient comfort issues 1, 6
• Venturi masks provide precise control of oxygen concentration (24%, 28%, 31%, 35%, 40%, and 60%) and are recommended for patients requiring accurate FiO2 delivery, particularly those at risk of hypercapnic respiratory failure, such as COPD patients 1, 7, 6

Non-Invasive Positive Pressure Ventilation

• Continuous positive airway pressure (CPAP) delivers constant positive pressure throughout the respiratory cycle and is used for preoxygenation before intubation, between intubation attempts to prevent hypoxemia, and for patients with impaired oxygenation 4, 8
• Bilevel positive airway pressure (BiPAP) provides two levels of positive pressure and is used for acute hypercapnic respiratory failure, although its effectiveness compared to HFNC is still being studied 5

Invasive Ventilation

• Endotracheal intubation is indicated when non-invasive methods fail to maintain adequate oxygenation or ventilation, and requires rapid sequence induction with preoxygenation, positioning, intravenous induction, and neuromuscular blockade, with confirmation of successful placement using waveform capnography 4, 8

Clinical Decision-Making Algorithm

• The American College of Physicians recommends an initial oxygen therapy approach for mild hypoxemia, starting with nasal cannula at 1-4 L/min (24-40% FiO2), and escalating to higher flow rates or switching to simple face masks or Venturi masks as needed, with consideration of HFNC for moderate to severe hypoxemia 1, 2, 6, 5
• The British Thoracic Society suggests that patients receiving non-invasive ventilation should be closely monitored and intubated promptly if they show signs of respiratory failure, with preparation for endotracheal intubation and use of HFNC or nasal cannula during intubation attempts to prevent desaturation 4, 8

Oxygen Delivery Method Selection: Nasal Cannula vs. Mask

Initial Oxygen Therapy Decision Algorithm

• For patients with severe hypoxemia, start with a reservoir mask at 15 L/min initially and adjust downward to nasal cannulae or simple face mask to maintain target saturation of 94-98% 9
• For patients with mild to moderate hypoxemia without critical illness, begin with nasal cannulae with flow rate adjusted to achieve target saturation of 94-98% 10

Patient-Specific Considerations

• For patients at risk of hypercapnic respiratory failure, use a 24% or 28% Venturi mask or nasal cannulae at low flow rates and target lower oxygen saturation (88-92%) 11, 9
• For patients with COPD with respiratory rate >30 breaths/min, increase flow rate above the minimum specified for Venturi masks 11

Advantages and Recommendations

• The British Thoracic Society recommends nasal cannulae for most patients requiring oxygen therapy due to better patient comfort, tolerance during meals, and equivalent clinical efficacy 11
• High-flow nasal cannulae are well tolerated and may be used as an alternative for patients requiring medium to high-concentration oxygen who are not at risk of hypercapnia 11, 12

Flow Rate Adjustments

• Nasal cannulae: 1-6 L/min (adjust to achieve target saturation) 11
• Simple face mask: 5-10 L/min (never below 5 L/min) 11
• Venturi mask: Flow rate specified for each concentration setting (higher flow needed if respiratory rate >30) 11
• Reservoir mask: 15 L/min 9

Nasal Cannula Oxygen During Cardioversion

Rationale for Leaving Nasal Cannula in Place

• Cardioversion is a brief procedure, and maintaining continuous oxygenation is more important than theoretical fire risk at low flow rates, according to the British Journal of Anaesthesia guidelines 13.
• Standard nasal cannula at ≤5 L/min does not generate significant aerosols and poses minimal infection control concerns, as stated by the Anaesthesia guidelines 14.

Clinical Algorithm for Oxygen Management During Cardioversion

• Ensure adequate preoxygenation before sedation if the patient will undergo procedural sedation, as recommended by the British Journal of Anaesthesia guidelines 13.

Important Caveats and Pitfalls

• The primary fire risk during cardioversion comes from high oxygen concentrations near ignition sources, but standard nasal cannula at typical flow rates does not create this risk, according to the Anaesthesia guidelines 14.
• Maintaining adequate oxygenation is more critical than removing oxygen delivery devices for brief procedures like cardioversion, as emphasized by the British Journal of Anaesthesia guidelines 13.

Special Considerations

• If the patient is on high-flow nasal cannula (HFNC) at 30-60 L/min, consider temporarily reducing flow to standard rates (5-6 L/min) during the actual shock delivery, then immediately resume HFNC afterward, as suggested by the European Respiratory Journal guidelines 15.
• If the patient is on NIV (CPAP or BiPAP), you must disconnect the device before cardioversion due to the occlusive mask interface and higher pressures, according to the European Respiratory Journal guidelines 16, 17.

Dual Oxygen Therapy with BiPAP and Nasal Cannula

Clinical Guidelines

• The British Thoracic Society recommends that nasal oxygen can be applied throughout airway management procedures, including during use of positive pressure devices, with standard nasal cannulae at 5 L/min during preoxygenation, increased to 15 L/min when consciousness is lost 18
• The American Academy of Sleep Medicine suggests optimizing BiPAP settings by increasing IPAP/EPAP as tolerated and ensuring proper mask fit to minimize leak, and maximizing oxygen flow through the BiPAP circuit, typically 10-15 L/min depending on the device 19
• For patients with COPD at risk of hypercapnic respiratory failure, the guideline is to target oxygen saturation of 88-92% even when using dual oxygen therapy, as excessive oxygen can worsen hypercapnia, according to the Thoracic Society 20

Practical Considerations

• The effective FiO2 delivered through the BiPAP circuit decreases as IPAP or EPAP increases due to higher intentional leak rates, so adding nasal cannula helps compensate for this phenomenon, as noted by the American Academy of Sleep Medicine 19
• If dual oxygen therapy fails, preparation for intubation is necessary, as this indicates BiPAP failure, according to the British Thoracic Society 18

Evidence‑Based Recommendations for Oxygen Delivery Devices

Low‑Flow Nasal Cannulae

• In adult patients, nasal cannulae deliver flow rates of 1–6 L/min, increasing the inspired FiO₂ by approximately 3–4 % for each additional litre and providing an overall FiO₂ range of 24 %–50 % 21, 22.
• At a flow of 2 L/min, the actual FiO₂ achieved varies widely between individuals, ranging from 24 % to 35 % 21, 22.

Simple Face Masks

• When set to flow rates of 5–10 L/min, simple face masks reliably produce an FiO₂ of 40 %–60 % 23.

Venturi (Fixed‑Performance) Masks

• Venturi masks are indicated for patients who require precise FiO₂ control—particularly those at risk of hypercapnic respiratory failure such as COPD patients 21, 22.
• For confused or cognitively impaired patients, Venturi masks are preferred because they reduce the risk of inadvertent flow‑rate errors 21, 22.

High‑Flow Nasal Cannula (HFNC)

• HFNC is not recommended for routine home‑oxygen therapy; its use is limited to acute care settings such as acute hypoxemic respiratory failure or post‑extubation support 21, 22.

Oxygen‑Conserving Devices

• These devices deliver oxygen only during the inspiratory phase, thereby minimizing waste during expiration 21, 22, 24.
• Clinical studies show that oxygen‑conserving devices can reduce overall oxygen consumption by up to 50 % 21, 22, 24.
• They are indicated for ambulatory patients who require high flow rates or who are active outside the home, but only after a formal ambulatory oxygen assessment 24.
• A notable limitation is the variable ability to maintain target SaO₂ during exercise; mouth‑breathing patients may fail to trigger the device, underscoring the need for pre‑prescription assessment 21, 22, 24.

Trans‑Tracheal Oxygen

• Delivered via a percutaneous catheter placed between the second and third tracheal rings, trans‑tracheal oxygen reduces anatomical dead space and allows lower oxygen flow rates compared with nasal cannulae, thereby decreasing the work of breathing 22, 24.
• Serious adverse events include catheter displacement, mucus obstruction, and infection 22, 24.
• Because of these risks, trans‑tracheal oxygen is rarely used in home settings and requires a dedicated, trained multidisciplinary team for implementation 21, 22, 24.

Selection of Oxygen Delivery Devices Based on FiO₂ Requirements and Clinical Status

Initial Device Choice for Most Patients

Low‑Flow Oxygen Delivery (FiO₂ ≈ 24–50 %)

Medium‑Concentration Oxygen (FiO₂ ≈ 40–60 %)

Precise FiO₂ Control for Hypercapnic‑Risk Patients (Venturi Masks)

High‑Concentration Oxygen (FiO₂ ≈ 60–90 %)

High‑Flow Nasal Cannula (HFNC) for Acute Hypoxemic Respiratory Failure

Oxygen‑Conserving Devices

Safety Pitfalls (Applicable Across Devices)

Oxygen Delivery Device Recommendations for Hypoxemia

1. Device Selection According to Severity of Hypoxemia

• For mild‑to‑moderate hypoxemia, the British Thoracic Society (BTS) recommends nasal cannulae at 1–6 L/min as first‑line therapy; for severe hypoxemia requiring high FiO₂, a high‑concentration reservoir mask at 15 L/min is preferred; patients who need precise FiO₂ control (e.g., at risk of hypercapnia) should receive Venturi masks. 27

2. Low‑Flow Oxygen Devices

2.1 Nasal Cannulae

• A flow of 1–4 L/min with a nasal cannula delivers an approximate FiO₂ of 24–40 %. 27
• Target SpO₂ is 94–98 % for most patients, but 88–92 % for those at risk of hypercapnic respiratory failure (e.g., COPD, obesity hypoventilation). 27, 28
• Advantages include superior patient comfort, ability to eat and speak, no CO₂ rebreathing, and lower cost. 27

2.2 Simple Face Mask

• Flow rates of 5–10 L/min deliver 40–60 % FiO₂. 27
• Flows < 5 L/min are unsafe because they cause dangerous CO₂ rebreathing and increase inspiratory resistance. 27

2.3 Venturi Mask (Precise FiO₂)

• Indicated for patients who require exact FiO₂, especially those at risk of hypercapnia (COPD, obesity hypoventilation). 27
• Provides fixed concentrations of 24 %, 28 %, 31 %, 35 %, 40 %, and 60 % oxygen. 27
• For patients with a respiratory rate > 30 breaths/min, the flow should be increased above the mask’s minimum to avoid dilution. 27

3. High‑Flow Oxygen Devices

3.1 High‑Concentration Reservoir Mask (Initial Management of Severe Hypoxemia)

• A flow of 15 L/min is the preferred method for delivering high‑concentration oxygen to critically ill patients. 27

3.2 High‑Flow Nasal Cannula (HFNC)

• The European Respiratory Society (ERS) states that HFNC is a potentially superior alternative to reservoir masks for acute hypoxemic respiratory failure without hypercapnia. 29, 28
• Initial settings: flow 40–50 L/min (range 35–60 L/min for adults), temperature 34–37 °C, FiO₂ titrated to achieve target SpO₂ (94–98 % or 88–92 % for hypercapnic‑risk patients). 30
• Physiologic benefits (moderate‑certainty evidence):
  
  • Delivers up to 60 L/min airflow, matching inspiratory demand. 30, 31
  • Provides reliable FiO₂ up to 100 %. 30
  • Generates low‑level PEEP (~7 cmH₂O at 50 L/min). 30
  • Supplies heated humidification, improving comfort and secretion clearance. 30, 31
  • Reduces CO₂ washout of the upper airways. 30
• Clinical outcomes (moderate certainty):
  
  • May reduce intubation rates (risk ratio 0.89; 95 % CI 0.77–1.02). 30
  • Shows similar short‑term mortality to conventional oxygen (RR 0.99; 95 % CI 0.84–1.17). 30
  • Significantly improves patient comfort versus reservoir masks. 30
  • Lowers respiratory rate by a mean 2.25 breaths/min. 30
  • Increases PaO₂ by a mean 16.7 mmHg. 30

4. Special Populations

4.1 Patients at Risk of Hypercapnic Respiratory Failure (COPD, Obesity Hypoventilation)

• Target SpO₂ 88–92 %. 27, 28
• Preferred devices: Venturi mask delivering 24 % or 28 % oxygen, or nasal cannula at 1–2 L/min. 27

4.2 Immunocompromised Patients

• HFNC is especially beneficial because it lowers the risk of ventilator‑associated complications such as pneumonia. 30, 31

5. Humidification Guidelines

• Not required for low‑flow oxygen (nasal cannulae or masks) or short‑term high‑flow use (e.g., pre‑hospital). 29, 28
• Indicated for high‑flow oxygen systems used > 24 h, for patients reporting upper‑airway dryness, those with tracheostomy or artificial airways, and for viscous secretions (may add nebulized saline). 29, 28
• HFNC always includes heated humidification as part of the system. 30, 31
• Bubble bottles (oxygen bubbling through water) should be avoided; they provide no clinical benefit and pose infection risk. 29, 28

6. Safety and Practical Considerations

• Never operate a simple face mask at < 5 L/min to avoid CO₂ rebreathing. 27
• Verify correct wall‑outlet connections; mis‑connecting oxygen tubing to compressed‑air outlets has caused adverse events. 27
• During nebulizer treatments, maintain the prescribed oxygen delivery and keep SpO₂ within target range. 29, 28