When should nasal prongs, a simple face mask, a non‑rebreather mask, non‑invasive ventilation, and endotracheal intubation be used in a patient?

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Last updated: April 29, 2026 • View editorial policy

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Oxygen Delivery Device Selection Algorithm

Start with nasal cannulae at 2-6 L/min for most hypoxaemic patients targeting SpO₂ 94-98%, escalate to a non-rebreather mask (NRBM) at 15 L/min if SpO₂ <85%, consider NIV for respiratory acidosis (pH <7.35 with elevated PaCO₂), and proceed to intubation if NIV fails or the patient deteriorates despite maximal support. 1

Initial Assessment and Device Selection

Step 1: Measure SpO₂ and Identify Risk Factors

For patients WITHOUT risk of hypercapnic respiratory failure (no COPD, obesity hypoventilation, neuromuscular disease):

  • SpO₂ ≥85%: Start with nasal cannulae at 2-6 L/min (preferred) or simple face mask at 5-10 L/min
  • SpO₂ <85%: Start immediately with non-rebreather mask (reservoir mask) at 15 L/min
  • Target range: 94-98% 1

For patients WITH risk of hypercapnic respiratory failure (COPD, obesity, neuromuscular disease):

  • Start with nasal cannulae at 1-2 L/min or 24-28% Venturi mask
  • Target range: 88-92% pending arterial blood gas results
  • If PaCO₂ is normal on blood gas, adjust target to 94-98% (unless history of previous hypercapnic respiratory failure requiring NIV)
  • Recheck blood gases after 30-60 minutes 1

Step 2: Device Characteristics and Flow Rates

Nasal Cannulae:

  • Flow rate: 2-6 L/min for standard patients, 1-2 L/min for hypercapnia risk
  • Preferred over simple face masks (better comfort, can eat/drink, cost-effective)
  • Delivers medium-concentration oxygen 1

Simple Face Mask:

  • Flow rate: 5-10 L/min (never <5 L/min to avoid CO₂ rebreathing)
  • Use when nasal cannulae insufficient
  • Less comfortable than nasal cannulae 1

Non-Rebreather Mask (NRBM/Reservoir Mask):

  • Flow rate: 15 L/min (fixed rate)
  • Critical indication: SpO₂ <85% on presentation
  • Delivers high-concentration oxygen (~60-90%)
  • Preferred device for critically ill patients until pulse oximetry stabilized 1

Venturi Masks:

  • Delivers precise FiO₂: 24%, 28%, 31%, 35%, 40%, 60%
  • Use when precise oxygen control needed (especially hypercapnia risk)
  • For respiratory rate >30/min, increase flow above minimum specified 1

Escalation Pathway

When to Escalate from Nasal Cannulae/Simple Mask to NRBM

Escalate immediately if:

  • Target saturation not maintained despite maximum flow
  • Patient requires senior medical assessment
  • Clinical deterioration (increased work of breathing, tachypnoea, tachycardia) 1

When to Consider Non-Invasive Ventilation (NIV)

Primary indications for NIV:

  • Respiratory acidosis: pH <7.35 with PaCO₂ >6.0 kPa despite optimal oxygen therapy
  • Acute hypercapnic respiratory failure (COPD exacerbation, obesity hypoventilation)
  • Acute cardiogenic pulmonary oedema (consider CPAP)
  • Persistent hypoxaemia despite high-flow oxygen 1, 2

NIV Setup:

  • Use full-face mask for general/non-specialist use 2
  • Initial settings: EPAP 3-5, IPAP 15 (or 20 if pH <7.25)
  • Target SpO₂ 88-92% in all patients on NIV
  • Monitor closely for synchronization, mask fit 2

Red flags indicating NIV failure (consider intubation):

  • pH <7.25 on optimal NIV
  • Respiratory rate persistently >25/min
  • New onset confusion or patient distress
  • Inability to protect airway
  • Haemodynamic instability 2

When to Intubate

Absolute indications:

  • Respiratory arrest or peri-arrest
  • Inability to protect airway (GCS <8, though not absolute)
  • Severe haemodynamic instability
  • NIV failure (worsening acidosis, hypoxaemia, or clinical deterioration) 2

Relative indications requiring senior assessment:

  • Persistent pH <7.25 despite NIV
  • Rapid desaturation when disconnected from NIV/high oxygen
  • Exhaustion, inability to cooperate with NIV
  • Copious secretions preventing NIV tolerance 2

Critical Pitfalls to Avoid

  1. Never use flow rates <5 L/min with simple face masks - causes CO₂ rebreathing 1

  2. Don't over-oxygenate COPD patients - target 88-92% initially, check blood gases within 30-60 minutes to avoid precipitating hypercapnic respiratory failure 1

  3. Don't delay escalation - if target saturations not achieved with nasal cannulae/simple mask, move to NRBM and ensure senior review 1

  4. Monitor blood gases closely - repeat ABG 30-60 minutes after any FiO₂ increase, especially in hypercapnia-risk patients 1

  5. Recognize NIV failure early - don't persist with failing NIV; early intubation has better outcomes than delayed intubation after prolonged NIV failure 2

  6. Bag-valve mask with leak is ineffective - if using for preoxygenation before intubation, ensure proper seal or use NRBM at flush rate oxygen instead 3

Special Considerations

Acute heart failure/pulmonary oedema: Consider CPAP or NIV early 1

Pneumothorax requiring observation: Use NRBM at 15 L/min targeting 100% saturation (accelerates pneumothorax resolution) 1

Most patients with MI, stroke, minor PE, pleural effusion, or anaemia: Often not hypoxaemic and don't require oxygen therapy unless SpO₂ <94% 1

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.