When is a non‑rebreathing mask indicated and what are the key considerations for its use?

Non-Rebreather Mask (Reservoir Mask)

A non-rebreather mask (reservoir mask) at 15 L/min is indicated for critically ill patients and those with severe hypoxemia (SpO₂ <85%) who are not at risk of hypercapnic respiratory failure, delivering 60-90% oxygen concentration to achieve target saturations of 94-98%. 11

Primary Indications

Critical Illness and Emergency Situations

• Cardiopulmonary resuscitation - Use highest feasible inspired oxygen during CPR 1
• Critical illness including major trauma, sepsis, shock, and anaphylaxis 1
• Severe acute hypoxemia with SpO₂ <85% (cause not yet diagnosed) 11
• Peri-arrest situations - Immediate use at 15 L/min while medical help is arriving 1

Specific Clinical Conditions Requiring Reservoir Mask

• Acute asthma with severe hypoxemia 1
• Pneumonia with SpO₂ <85% 1
• Deterioration of lung fibrosis or interstitial lung disease with SpO₂ <85% 1
• Pneumothorax requiring observation - Use 15 L/min targeting 100% saturation (oxygen accelerates pneumothorax clearance) 11
• Carbon monoxide poisoning - Aim for 100% saturation regardless of oximetry reading 1
• Major head injury - Initial treatment pending blood gas results or airway securing 1
• Drowning - Until spontaneous circulation restored 1

Key Operational Considerations

Flow Rate and Oxygen Delivery

• Always use 15 L/min flow rate - This is non-negotiable for proper function 11
• Delivers 60-90% oxygen concentration depending on mask fit and breathing pattern 11
• The delivered concentration is variable and depends on mask seal and patient's inspiratory flow rate 1

Target Oxygen Saturations

• Standard target: 94-98% for most patients without hypercapnia risk 11
• Modified target: 88-92% for patients with COPD or hypercapnic respiratory failure risk (only as initial treatment in critical illness, then adjust based on blood gases) 1

Titration Strategy

Once patient stabilizes with reliable oximetry:

1. Step down to nasal cannulae (1-6 L/min) or simple face mask (5-10 L/min) to maintain target saturation 1
2. Allow at least 5 minutes at each dose before further adjustment 1
3. Obtain arterial blood gas within 1 hour if requiring increased oxygen 1
4. Seek senior medical input immediately when reservoir mask is required 11

Critical Pitfalls and Contraindications

When NOT to Use Reservoir Mask

Avoid or use with extreme caution in:

• Hypercapnic respiratory failure risk - Use 24-28% Venturi mask instead unless critically ill 1
• COPD with known oxygen sensitivity - Target 88-92% saturation, consider lower concentration devices 1
• Paraquat poisoning or bleomycin lung injury - Target only 85-88% if oxygen needed 1
• Prolonged use in pulmonary disease - Duration >2 hours may increase mortality 2

Common Errors to Avoid

• Inadequate flow rate - Never use <15 L/min; this compromises oxygen delivery 1
• Mask leak - Even with flush rate oxygen, significant mask leak dramatically reduces efficacy (FeO₂ drops to 30%) 3
• Unnecessary use - Many conditions (minor PE, stable MI, stroke, mild anemia) don't require oxygen therapy at all 11
• Delayed escalation - If reservoir mask fails to achieve target saturation, immediately seek senior/specialist advice and consider NIV or intubation 11

Evidence-Based Alternatives

When Reservoir Mask Unavailable or Ineffective

• High-flow nasal cannula (HFNC) - Consider as alternative for acute respiratory failure without hypercapnia 11
• Bag-valve mask at flush rate - For preoxygenation before intubation, though NRB at flush rate is noninferior 43

Comparative Effectiveness

Recent research shows flush rate oxygen (40-60 L/min) with NRB is noninferior to bag-valve mask for preoxygenation in healthy volunteers 43, though one study in COVID-19 patients showed higher device failure rates with HFNC compared to NRB 5. The key advantage of NRB is simplicity and reduced risk of mask leak compared to bag-valve mask 3.

Monitoring Requirements

Mandatory assessments:

• Continuous pulse oximetry monitoring
• Respiratory rate and heart rate (tachypnea/tachycardia more common than cyanosis) 1
• Arterial blood gas within 30-60 minutes if patient has COPD risk factors 1
• Arterial blood gas within 1 hour if requiring escalation to reservoir mask 1
• Consider NIV or invasive ventilation if target saturation not achieved 1