Methods of Administering Oxygen

1. Low-Flow Systems

Nasal Cannula

• Flow rate: 1-6 L/min in adults
• Estimated FiO2: ~24-44%
• Prongs sit in the nostrils and deliver a constant flow that pools in the nasopharynx, acting as a small reservoir
• FiO2 varies inversely with respiratory rate; faster breathing = lower FiO2 at the same flow
• Most comfortable and commonly used device; does not interfere with eating or talking
• Flows ≤4 L/min typically do not require humidification
• Can be used at higher flows briefly (e.g. 15 L/min for apneic oxygenation during intubation)

Simple Face Mask

• Flow rate: 5-10 L/min (minimum 5 L/min to flush exhaled CO2)
• Estimated FiO2: ~35-50%
• A plastic mask that covers the nose and mouth; side exhalation ports allow CO2 washout
• Less comfortable than a nasal cannula; interferes with eating and talking

Partial Rebreather Mask

• Flow rate: 6-10 L/min
• Estimated FiO2: ~40-70%
• Has an attached reservoir bag; the first third of each exhalation (dead-space gas, rich in O2) re-enters the bag for re-breathing
• Exhalation ports remain open

Non-Rebreather Mask (NRB)

• Flow rate: 10-15 L/min
• Estimated FiO2: up to ~60-80% (theoretical 100%, practically ~60-80% due to mask fit)
• Reservoir bag + one-way valves prevent mixing with room air
• Best high-concentration option without invasive airways
• Used in emergencies (trauma, carbon monoxide poisoning, pneumothorax)

Nasal Catheter / Nasopharyngeal Catheter

• A thin catheter passed through the nostril to the nasopharynx
• Can deliver oxygen when mask compliance is poor
• Less commonly used today

2. High-Flow Systems

Venturi Mask (Air-Entrainment Mask)

• Flow rate depends on selected valve/color-coded adapter
• Fixed, precise FiO2: 24%, 28%, 31%, 35%, 40%, 60%
• Uses the Venturi principle: high-pressure O2 jet entrains a fixed ratio of room air
• Preferred in COPD and conditions where precise FiO2 control matters (e.g. avoiding hypercapnic drive suppression)

High-Flow Nasal Cannula (HFNC)

• Flow rate: up to 60 L/min; FiO2: up to >90%
• Delivers heated, humidified gas via wider nasal prongs
• Washes out nasopharyngeal dead space, reduces work of breathing, provides mild CPAP effect (~1-2 cmH2O per 10 L/min)
• Evidence supports use in hypoxic respiratory failure; good tolerance; allows talking and eating
• Example: Optiflow system

Aerosol/Tracheostomy Mask and T-Piece

• Used for patients with tracheostomies or endotracheal tubes
• A face tent or T-shaped connector delivers humidified oxygen directly
• FiO2 depends on flow rate and device configuration

3. Ventilatory Support Methods

Bag-Valve-Mask (BVM / Ambu Bag)

• Manual device: self-inflating bag + one-way valve + face mask
• Can deliver up to 100% FiO2 when connected to O2 with a reservoir bag
• Used in apnea, pre-oxygenation before intubation, and rescue ventilation
• Proper technique: tidal volume ~500 mL over 1-1.5 seconds; C-E clamp for mask seal
• Two-rescuer technique preferred (one seals mask with two hands, one squeezes bag)

CPAP (Continuous Positive Airway Pressure)

• Non-invasive; delivers a constant positive pressure throughout the respiratory cycle
• Recruits collapsed alveoli, reduces work of breathing, improves oxygenation
• FiO2 adjustable up to 100%
• Used in obstructive sleep apnea, acute pulmonary edema, mild-moderate hypoxic failure

BiPAP / NIV (Non-Invasive Positive Pressure Ventilation)

• Delivers two pressure levels: higher inspiratory (IPAP) and lower expiratory (EPAP)
• Provides both oxygenation support and ventilatory assistance
• First-line in COPD exacerbations, type II respiratory failure, cardiogenic pulmonary edema

Mechanical Ventilation (Invasive)

• Oxygen delivered via endotracheal tube (ETT) or tracheostomy
• Full control of FiO2 (21-100%), tidal volume, respiratory rate, PEEP
• Modes: volume-controlled, pressure-controlled, SIMV, pressure support, etc.
• Used in severe respiratory failure, unconsciousness, or when airway protection is needed

Laryngeal Mask Airway (LMA)

• A supraglottic airway device seated over the larynx
• Can deliver O2 without tracheal intubation; less invasive than ETT
• Used for elective airway management and as a rescue device after failed intubation

4. Specialized Methods

Summary Table