When should a patient be put on high flow oxygen (O2)?

When to Initiate High-Flow Oxygen Therapy

High-flow nasal oxygen (HFNO) should be considered as an alternative to reservoir mask treatment in patients with acute respiratory failure without hypercapnia who are not responding adequately to conventional oxygen delivery methods. 1

Primary Indications for High-Flow Oxygen

Acute Hypoxemic Respiratory Failure (Type I)

• HFNO is indicated when patients require high oxygen concentrations (typically needing reservoir mask at 15 L/min) but are not achieving target saturations of 94-98% with conventional oxygen therapy. 1, 2
• Patients with severe hypoxemia (SpO2 <85%) who would otherwise require reservoir masks are excellent candidates for HFNO as an escalation option. 3
• HFNO has been shown to reduce intubation rates compared to conventional oxygen therapy in acute hypoxemic respiratory failure. 4, 5

Specific Clinical Scenarios

Severe COVID-19 pneumonia: HFNO significantly decreased the need for mechanical ventilation (34.3% vs 51.0%) and reduced time to clinical recovery (11 vs 14 days) compared to conventional oxygen therapy. 6

Pneumonia with desaturation: When patients require escalating oxygen despite nasal cannulae or simple face masks, HFNO should be considered before progressing to reservoir masks or intubation. 3, 7

Respiratory rate >30 breaths/min: This indicates respiratory distress requiring immediate intervention, even if SpO2 appears adequate—HFNO is an appropriate escalation at this point. 3

Mechanisms That Make HFNO Superior

HFNO provides several physiological advantages over conventional oxygen: 5, 7

• Delivers precise FiO2 up to 100% at flow rates of 30-60 L/min
• Creates positive end-expiratory pressure (PEEP) effect generating alveolar recruitment
• Washes out dead space in upper airways
• Reduces work of breathing through decreased inspiratory resistance
• Improves mucociliary clearance through heated and humidified gas
• Prevents dilution of inspired oxygen by ambient air

Clinical Algorithm for HFNO Initiation

Step 1 - Initial oxygen requirement: 1, 2, 3

• SpO2 <94%: Start conventional oxygen (nasal cannulae 2-6 L/min or simple face mask 5-10 L/min)
• SpO2 <85%: Start reservoir mask at 15 L/min

Step 2 - Assess response after 5 minutes: 3

• If target saturation (94-98%) not achieved or patient requires increasing FiO2 to maintain constant saturation, consider HFNO

Step 3 - Identify high-risk features for HFNO: 3, 5

• Respiratory rate >30 breaths/min despite adequate SpO2
• Increasing oxygen requirements over time
• Work of breathing remains high despite oxygen therapy
• Patient discomfort or intolerance of reservoir mask

Contraindications and Cautions

Do NOT use HFNO as first-line in hypercapnic respiratory failure (Type II). In patients with COPD or other conditions causing CO2 retention, non-invasive ventilation (NIV) should be preferred, as HFNO data are inconclusive in this population. 4, 8

Adjust target saturations for at-risk patients: 1, 2

• Standard target: 94-98% SpO2
• COPD/hypercapnic risk: 88-92% SpO2

Critical Monitoring Requirements

Patients on HFNO are critically ill and require: 8

• Continuous pulse oximetry monitoring
• Regular assessment of respiratory rate, work of breathing, and mental status
• Arterial blood gas analysis if clinical deterioration occurs or SpO2 falls below target despite HFNO 2, 3
• Immediate availability of intubation capability—HFNO is not a substitute for mechanical ventilation when indicated 8

Additional Applications Beyond Acute Respiratory Failure

HFNO can also be used for: 5, 8

• Preoxygenation before intubation
• Post-extubation support to prevent reintubation
• Oxygenation during bronchoscopy in hypoxemic patients
• Support in obese patients with respiratory compromise

Key Pitfall to Avoid

The most dangerous error is delaying intubation in a deteriorating patient on HFNO. HFNO may temporarily improve oxygenation while the underlying condition worsens—if the patient shows signs of exhaustion, worsening mental status, or inability to protect airway, proceed immediately to intubation rather than persisting with HFNO. 8