When should a non-rebreather (NRB) mask be used versus BIPAP (Bilevel Positive Airway Pressure) or CPAP (Continuous Positive Airway Pressure)?

When to Use Non-Rebreather Versus BIPAP or CPAP

Non-rebreather masks should be used for patients with hypoxemic respiratory failure without hypercapnia, while CPAP is indicated for hypoxemic respiratory failure requiring recruitment of underventilated lung, and BiPAP should be used for patients with hypercapnic respiratory failure or increased work of breathing.

Non-Rebreather Mask (NRB)

Indications:

• Type 1 respiratory failure (hypoxemia without hypercapnia)
• Trauma and emergency situations requiring high oxygen concentration
• Short-term oxygen therapy when carbon dioxide retention is unlikely
• Oxygen delivery in the 60-90% range at 15 L/min flow rate 1

Advantages:

• Simple to deploy and use
• Delivers relatively high FiO2 (60-90%)
• Does not require electricity or specialized equipment
• Appropriate for initial management of acute hypoxemia

Limitations:

• Not suitable for patients with hypercapnic (type 2) respiratory failure
• Risk of carbon dioxide rebreathing at low flow rates
• Performance decreases with high respiratory rates
• Prolonged use (>2 hours) in patients with pulmonary disease may increase mortality 2

Continuous Positive Airway Pressure (CPAP)

Indications:

• Hypoxemic respiratory failure requiring recruitment of underventilated lung
• Offsetting intrinsic PEEP in COPD patients
• Obstructive sleep apnea
• Cardiogenic pulmonary edema

Mechanism of action:

• Increases mean airway pressure
• Improves ventilation to collapsed areas of lung
• Recruits underventilated lung (similar to PEEP in intubated patients)
• Unloads inspiratory muscles and reduces work of breathing 1

Settings:

• Initial CPAP typically 5-10 cmH2O
• Can be increased to 12-15 cmH2O if needed
• Target SpO2 90-96% (or 92-95% in pregnant patients) 1

Bilevel Positive Airway Pressure (BiPAP)

Indications:

• Type 2 respiratory failure (hypercapnia)
• COPD exacerbations
• Neuromuscular disorders with respiratory muscle weakness
• Patients with poor respiratory drive
• Patients who cannot tolerate CPAP due to discomfort from high pressures 3

Mechanism of action:

• Provides inspiratory positive airway pressure (IPAP) for ventilation
• Expiratory positive airway pressure (EPAP) recruits lung and offsets intrinsic PEEP
• Can be set with backup rate (ST mode) for patients with central hypoventilation or unreliable triggering 1, 3

Settings:

• Initial IPAP of 8 cmH2O, EPAP of 4 cmH2O
• Minimum IPAP-EPAP differential of 4 cmH2O
• Backup rate equal to or slightly less than spontaneous sleeping respiratory rate (minimum 10 breaths/min) 3

Decision Algorithm for Oxygen Therapy Selection

1. Assess respiratory failure type:

   • Type 1 (hypoxemia without hypercapnia): Consider NRB or CPAP
   • Type 2 (hypercapnia): Consider BiPAP

2. For hypoxemic patients (Type 1):

   • If mild to moderate hypoxemia and no increased work of breathing: Start with NRB
   • If severe hypoxemia or increased work of breathing: Consider CPAP
   • If using NRB and patient requires >15 L/min oxygen or has high respiratory rate: Switch to CPAP

3. For hypercapnic patients (Type 2):

   • BiPAP is first-line therapy
   • Set appropriate IPAP/EPAP differential to assist ventilation
   • Consider ST mode if poor respiratory drive

4. Monitoring and escalation:

   • Assess response within 1-2 hours of NIV initiation
   • If no improvement or deterioration occurs, consider intubation
   • For NRB, avoid prolonged use (>2 hours) in patients with pulmonary disease 1, 2

Important Considerations and Pitfalls

• Carbon dioxide retention risk: NRB masks are not suitable for patients with hypercapnic respiratory failure due to risk of further CO2 retention 1

• Flow requirements: High respiratory rates may exceed the flow capabilities of standard oxygen delivery systems; CPAP generators need to maintain desired pressure throughout the respiratory cycle 1, 4

• Monitoring: Close monitoring is essential when using NIV, with assessment within 1-2 hours to prevent delay in intubation if needed 1

• Mask fit: Proper mask fit is crucial for effective oxygen delivery with any system; leaks significantly reduce effectiveness 1, 3

• Aerosol generation: Both CPAP and BiPAP are aerosol-generating procedures, which may increase risk of disease transmission in infectious conditions 1

By following this algorithm and understanding the specific indications for each oxygen delivery method, clinicians can optimize respiratory support while minimizing risks associated with inappropriate device selection.