Provide comprehensive, point‑wise notes on oxygen delivery devices, covering indications, flow rates, FiO₂ ranges, advantages, disadvantages, humidification, monitoring, and escalation for exam preparation.

Oxygen Delivery Devices: Comprehensive Exam Notes

Low-Flow Oxygen Delivery Systems

Nasal Cannula

Nasal cannula is the first-line oxygen delivery device for most patients requiring supplemental oxygen. 1

Flow Rates and FiO₂ Delivery

• Flow range: 1–6 L/min delivering approximately 24–50% FiO₂ 2
• Each additional liter increases FiO₂ by approximately 3–4% 2, 3
• At 2 L/min: FiO₂ ranges from 24–35% (wide individual variation) 2
• At 5 L/min: approximately 40% FiO₂ 4
• The actual FiO₂ cannot be precisely predicted due to variations in respiratory rate, tidal volume, and breathing pattern 2, 4

Advantages

• Superior patient comfort compared to masks 1, 2
• Can be worn during meals and speech 1, 2
• Less likely to be removed by patients 1
• No risk of CO₂ rebreathing 2, 4
• Lower inspiratory resistance than face masks 1
• More cost-effective 4
• No claustrophobic sensation 4

Disadvantages

• Unpredictable FiO₂ delivery makes it unsuitable when exact oxygen concentration is required (e.g., calculating A-a gradient) 2, 4
• Nasal irritation or soreness, especially at flow rates >4 L/min 4
• Reduced effectiveness with severe nasal congestion 4
• Flow rates must be adjusted based on pulse oximetry and arterial blood gas results 2, 4

Clinical Pearls

• Mouth breathing does NOT reduce effectiveness—it may actually result in the same or higher inspired oxygen concentration 4, 3
• Most centers advocate humidification, although evidence for non-heated humidification is lacking 1
• For ambulatory patients, low-flow 100% oxygen is easily adjusted by caregivers to match activity levels 1

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Simple Face Mask

Flow Rates and FiO₂ Delivery

• Flow range: 5–10 L/min delivering 40–60% FiO₂ 2, 3
• CRITICAL: Never use flow rates below 5 L/min—this causes dangerous CO₂ rebreathing and increased inspiratory resistance 2

Disadvantages

• Less comfortable than nasal cannula 2
• Must be removed for meals 2
• Less preferred than nasal cannula for medium-concentration oxygen therapy 2

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Venturi (Fixed-Performance) Masks

Venturi masks are mandatory for patients requiring precise FiO₂ control, particularly those at risk of hypercapnic respiratory failure. 1, 2

Available Concentrations

• Fixed FiO₂ options: 24%, 28%, 31%, 35%, 40%, and 60% 1, 2
• Each concentration requires manufacturer-specified flow rates 2

Indications

• Patients at risk of hypercapnic respiratory failure (COPD, obesity hypoventilation syndrome) 1, 2
• Patients with high resting respiratory rate (>30 breaths/min) 1, 2
• Confused or cognitively impaired patients to prevent inadvertent flow-rate errors 1, 2

Critical Adjustment

• For respiratory rate >30 breaths/min, increase flow rate above the minimum specified to maintain intended FiO₂ 1, 2

Target Oxygen Saturation

• For hypercapnic-risk patients: target SpO₂ 88–92% (not 94–98%) 2, 4
• Use 24% or 28% Venturi mask or nasal cannula at 1–2 L/min 2

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High-Flow Oxygen Delivery Systems

High-Flow Nasal Cannula (HFNC)

HFNC is indicated for acute hypoxemic respiratory failure and post-extubation respiratory support, NOT for routine home oxygen therapy. 2

Flow Rates and Settings

• Flow range: 30–70 L/min 2
• Initial settings: 40–50 L/min (range 35–60 L/min for adults) 2
• Temperature: 34–37°C 2
• FiO₂ titrated to achieve target SpO₂ (94–98% or 88–92% for hypercapnic-risk patients) 2

Physiologic Benefits (Moderate-Certainty Evidence)

• Delivers up to 60 L/min airflow, matching inspiratory demand 2
• Provides reliable FiO₂ up to 100% 2
• Generates low-level PEEP (~7 cmH₂O at 50 L/min) 2
• Supplies heated humidification, improving comfort and secretion clearance 2
• Reduces CO₂ washout of upper airways 2

Clinical Outcomes (Moderate Certainty)

• May reduce intubation rates (risk ratio 0.89; 95% CI 0.77–1.02) 2
• Similar short-term mortality to conventional oxygen (RR 0.99; 95% CI 0.84–1.17) 2
• Significantly improves patient comfort versus reservoir masks 2
• Lowers respiratory rate by mean 2.25 breaths/min 2
• Increases PaO₂ by mean 16.7 mmHg 2
• Reduces re-intubation risk (4.9% vs 12.2%; p = 0.04) 2

Special Population

• Especially beneficial for immunocompromised patients due to lower risk of ventilator-associated pneumonia 2

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High-Concentration Reservoir (Non-Rebreather) Mask

Flow Rates and FiO₂ Delivery

• Flow rate: 15 L/min delivering 60–90% FiO₂ 2
• Preferred initial method for severe hypoxemia in critically ill patients 2

Clinical Algorithm

• Start with reservoir mask at 15 L/min for severe hypoxemia 2
• Adjust downward to nasal cannula or simple face mask once target saturation (94–98%) is achieved 2

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Specialized Oxygen Delivery Systems

Oxygen-Conserving Devices

These devices deliver oxygen only during inspiration, reducing oxygen consumption by up to 50%. 1, 5

Types

• Transtracheal catheters 5
• Reservoir cannulas 5
• Demand oxygen delivery systems 5

Mechanism

• Deliver oxygen only during inspiratory phase, minimizing waste during expiration 2, 5
• Transtracheal catheters increase effective FiO₂ by approximately 5% per liter (compared to 2.5% per liter with nasal cannula) 6

Indications

• Ambulatory patients requiring high flow rates 1
• Patients active outside the home 1
• Only after formal ambulatory oxygen assessment 1

Limitations

• Variable ability to maintain target SaO₂ during exercise 1
• Mouth-breathing patients may fail to trigger the device 1
• Pre-prescription assessment is mandatory 1

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Trans-Tracheal Oxygen

Trans-tracheal oxygen is rarely used in home settings and requires dedicated support from a trained team. 1

Mechanism

• Oxygen delivered via catheter inserted percutaneously between second and third tracheal rings 1
• Reduces anatomical dead space, allowing lower oxygen flow rates than nasal cannula 1, 2
• Reduces work of breathing 1, 2

Serious Complications

• Catheter displacement 1, 2
• Obstruction by mucus 1, 2
• Infection 1, 2

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Oxygen via Tracheostomy

Delivery Method

• Tracheostomy collar is most widely used 1
• Most centers advocate enhanced humidification 1

Critical Requirement

• Patients receiving oxygen via tracheostomy MUST receive humidified oxygen to maintain patent airway, reduce secretion buildup, and minimize discomfort 1

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Face Tents and Head Hoods

Disadvantages

• Limit mobility and visibility of patient 1
• CO₂ can build up with insufficient flow rates 1
• Temperature and moisture buildup 1
• These problems complicate widespread usage 1

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Oxygen Delivery System Selection

Source Options

• Compressed gas cylinders 1
• Liquid oxygen 1
• Oxygen concentrators 1

Selection Criteria

• Flow and concentration of oxygen needed 1
• Equipment availability from local vendors 1
• Insurance coverage 1

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Humidification Guidelines

When Humidification is NOT Required

• Low-flow oxygen (nasal cannula or masks) 2
• Short-term high-flow use (e.g., pre-hospital) 2

When Humidification is Indicated

• High-flow oxygen systems used >24 hours 2
• Patients reporting upper-airway dryness 2
• Patients with tracheostomy or artificial airways 1, 2
• Viscous secretions (may add nebulized saline) 2
• HFNC always includes heated humidification as part of the system 2

What to Avoid

• Bubble bottles (oxygen bubbling through water) should be avoided—they provide no clinical benefit and pose infection risk 2

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Clinical Decision Algorithm for Hypoxemia

Mild-to-Moderate Hypoxemia

1. Start with nasal cannula at 1–4 L/min (24–40% FiO₂) 2
2. Target SpO₂ 94–98% for most patients 2
3. Adjust flow based on pulse oximetry 2

Severe Hypoxemia

1. Start with high-concentration reservoir mask at 15 L/min 2
2. Consider HFNC if hypoxemia persists without hypercapnia 2
3. Prepare for intubation if non-invasive methods fail 2

Hypercapnic-Risk Patients (COPD, Obesity Hypoventilation)

1. Use Venturi mask at 24% or 28% OR nasal cannula at 1–2 L/min 2
2. Target SpO₂ 88–92% (NOT 94–98%) 2, 4
3. At 6 L/min via nasal cannula, hypercapnia can develop within 15 minutes 4
4. When precise FiO₂ control is unavailable, limit high-flow oxygen to maximum 6 minutes 4

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Monitoring and Escalation

Monitoring Parameters

• Pulse oximetry (SpO₂) 2
• Arterial blood gas when indicated 2
• Respiratory rate 2
• Work of breathing 2

Escalation Pathway

1. Nasal cannula (1–6 L/min) 2
2. Simple face mask (5–10 L/min) OR Venturi mask (for precise FiO₂) 2
3. High-concentration reservoir mask (15 L/min) 2
4. High-flow nasal cannula (30–70 L/min) 2
5. Non-invasive positive pressure ventilation (CPAP/BiPAP) 2
6. Endotracheal intubation and mechanical ventilation 2

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Safety Considerations and Common Pitfalls

Critical Safety Points

• Never use simple face mask below 5 L/min—causes dangerous CO₂ rebreathing 2
• Verify correct wall-outlet connections—mis-connecting oxygen tubing to compressed-air outlets has caused adverse events 2
• During nebulizer treatments, maintain prescribed oxygen delivery and keep SpO₂ within target range 2

Common Pitfalls to Avoid

• Do NOT assume nasal cannula delivers a consistent FiO₂—the same flow rate can have widely different effects in different patients 2, 4
• Do NOT assume nasal cannula is ineffective in mouth breathers—mouth breathing often increases delivered oxygen concentration 4, 3
• Do NOT target SpO₂ 94–98% in hypercapnic-risk patients—target 88–92% instead 2, 4

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Special Circumstances: Traveling with Oxygen

Altitude and Airline Travel

• Commercial aircraft maintain cabin altitudes between 6,000–8,000 feet 1
• At 8,000 feet, inspired PO₂ is 118 mmHg (versus 159 mmHg at sea level) 1
• Patients on supplemental oxygen will require enhanced FiO₂ at altitude 1

Formula to Estimate Required FiO₂

FiO₂ (BP – 47) [ground level] = FiO₂ (BP – 47) [altitude] 1

• BP = barometric pressure in mmHg 1

Practical Recommendations

• Contact airline well in advance 1
• Attempt to utilize direct flights 1
• Arrange oxygen availability between flights for oxygen-dependent patients 1
• Hypoxic challenge testing (15–16% inspired oxygen) can predict effect of airline travel 1

Transporting Oxygen in Vehicles

• Cylinders should be secured with seat belt, or in foot-well or car boot 1
• Liquid oxygen must always be transported upright 1
• Warning triangle may be displayed 1
• Insurance companies should be informed 1

Portable Oxygen Equipment

• Trolleys or wheeled devices improve quality of life, distance walked, and symptoms in patients who can walk >300 meters 1
• Less able patients find trolleys easier to use than backpacks 1

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Device Performance at Varying Respiratory Rates

Variable Performance Systems (Nasal Cannula, Simple Face Mask)

• Deliver significantly reduced oxygen concentration at high respiratory rates 7

Fixed Performance Systems (Venturi Masks)

• Deliver appropriate oxygen concentrations across range of respiratory rates for 24–40% settings 7
• 60% Venturi masks show reduction in performance at high respiratory rates 7

High-Flow Systems

• Show no failure of performance at increased respiratory rates 7