Non Rebreather Mask (NRBM) 

Components & Design

1. Reservoir Bag

• Capacity: ~600–1000 mL
• Must remain partially inflated at all times
• Acts as an oxygen reservoir → prevents dilution

2. One-Way Valves

• Between mask & bag: allows O₂ flow into mask but prevents exhaled gas entering bag
• Side ports (exhalation valves):
• Prevent room air entrainment during inspiration
• Allow CO₂ to escape during expiration

Working Principle 

Inspiration:

• Patient inhales oxygen from:
• Reservoir bag
• Direct oxygen flow
• One-way valves prevent room air entry

Expiration:

• Exhaled gases exit through side ports
• Valve prevents gas from entering reservoir bag

 Net effect → minimal rebreathing + high FiO₂ delivery

Oxygen Delivery & FiO₂

Key Concept:

• True 100% FiO₂ is NOT achieved due to:
• Mask leaks
• Variable inspiratory flow
• Valve inefficiency

Indications

Emergency / ICU Indications

• Acute hypoxemic respiratory failure
• Severe pneumonia
• ARDS (initial stabilization)
• Pulmonary edema
• Trauma / shock
• Carbon monoxide poisoning (bridge therapy)

Preoxygenation

• Before intubation (RSI)
• During apneic oxygenation (with nasal cannula adjunct)

Contraindications

Absolute

• Apnea (needs ventilation, not NRBM)

Relative

• COPD with CO₂ retention (risk of worsening hypercapnia)
• Altered sensorium → aspiration risk
• Facial trauma → poor seal

NRBM vs Other Oxygen Devices

Clinical Pro Tip (ICU)

 If patient on NRBM has:

• RR > 30
• SpO₂ < 90%
• Increased work of breathing

➡️ Do NOT persist → escalate immediately (HFNC/NIV/intubation)