What are the guidelines for initiating and managing High Flow Nasal Cannula (Hfnc) therapy in patients requiring oxygen therapy?

High Flow Nasal Cannula (HFNC) Therapy: Initiation and Management Guidelines

When to Initiate HFNC

HFNC should be used as an alternative oxygen delivery system for adult patients requiring medium-to-high concentration oxygen therapy who are not at risk of hypercapnia, particularly when conventional oxygen therapy fails to maintain target saturations or when enhanced patient comfort is needed. 1

Primary Indications

• Hypoxemic respiratory failure: Use HFNC when patients fail to maintain SpO2 94-98% despite nasal cannulae (up to 6 L/min) or simple face masks (5-10 L/min) 1, 2
• Post-extubation support: HFNC reduces reintubation risk (4.9% vs 12.2% with conventional oxygen) within 72 hours in mechanically ventilated patients at low risk of reintubation 1
• Acute hypoxemic respiratory failure: HFNC provides better oxygenation, lower respiratory rates, and superior patient comfort compared to conventional face masks 1, 3

Contraindications and Cautions

• Do NOT use HFNC as first-line therapy in hypercapnic respiratory failure (e.g., COPD exacerbations with CO2 retention) - non-invasive ventilation (NIV) should be preferred instead 4, 5
• Avoid in patients requiring immediate intubation - HFNC is for patients who can be monitored continuously and where escalation to invasive ventilation is immediately available 4

Initial HFNC Settings

Flow Rate

• Start with 40-50 L/min for adults as the initial flow rate 5
• Higher flows (50-60 L/min) provide greater physiological benefit through enhanced PEEP effect and dead space washout, particularly in hypoxemic respiratory failure 5, 1
• Maximum tolerated flow is typically 60 L/min, though some patients cannot tolerate flows above 40-50 L/min despite theoretical benefits 5

FiO2 (Fraction of Inspired Oxygen)

• Titrate FiO2 to achieve target SpO2 of 94-98% for patients without risk of hypercapnia 5, 1
• Target SpO2 88-92% for patients at risk of hypercapnic respiratory failure (e.g., those with COPD or previous CO2 retention) 5, 1
• Adjust FiO2 in 5-10% increments to maintain target saturations 5

Temperature

• Set temperature between 34-37°C according to patient preference 5
• Higher temperatures (37°C) provide optimal humidification and prevent airway drying 5, 1

Monitoring Requirements

Continuous Monitoring Parameters

Patients on HFNC are critically ill and require continuous monitoring with immediate access to escalation of care. 4

• Respiratory rate: Should decrease with effective HFNC therapy; respiratory rate >30 breaths/min requires immediate escalation even with adequate SpO2 5, 6
• Oxygen saturation: Continuous pulse oximetry monitoring 5
• Work of breathing: Assess for accessory muscle use and patient comfort 5
• Arterial blood gases: Check within 30-60 minutes if clinical deterioration occurs or when initiating/increasing oxygen therapy 1, 6

Signs Requiring Escalation

• pH <7.35 with elevated PaCO2 >6.0 kPa: Indicates respiratory acidosis requiring immediate senior review and consideration of NIV or invasive ventilation 1
• Persistent hypoxemia despite FiO2 >0.6: Consider intubation 3
• Increasing respiratory distress or altered mental status: Prepare for immediate intubation 4

Titration Algorithm

Adjusting Flow Rate

• Increase flow by 5-10 L/min if patient shows increased work of breathing or respiratory distress 5
• Decrease flow by 5-10 L/min if patient experiences discomfort at higher flows 5
• Adjust flow based on patient comfort and respiratory effort, not just oxygen saturation alone 5

Adjusting FiO2

• Increase FiO2 in 5-10% increments if SpO2 falls below target range 5
• Decrease FiO2 gradually once SpO2 stabilizes above target, considering reduction if PaO2 >8.0 kPa 1
• Avoid excessive oxygen: High oxygen concentrations may cause oxygen toxicity and potential harm 5

Weaning from HFNC

Weaning Criteria

Patients are ready for weaning when they maintain target SpO2 with flow ≤20 L/min and FiO2 ≤0.3. 7

Weaning Strategy

• Reduce both flow and FiO2 simultaneously: Decrease flow by 10 L/min/hour and FiO2 by 0.1/hour until reaching 20 L/min and 0.3 FiO2 7
• Alternative approach: Reduce flow first by 10 L/min/hour to 20 L/min, then reduce FiO2 by 0.1/hour to 0.3 7
• Transition to conventional oxygen therapy (nasal cannulae at 1-6 L/min) once weaning targets are achieved 7, 1

Common Pitfalls to Avoid

• Inadequate initial flow rate: Starting with flows <40 L/min may provide insufficient PEEP effect and dead space washout 5
• Delayed escalation to intubation: Prolonged HFNC trial in deteriorating patients leads to worse outcomes - prepare for intubation early 5, 4
• Using HFNC in hypercapnic respiratory failure: NIV should be first-line; HFNC may be used during NIV breaks but not as primary therapy 5, 4
• Poor interface fit: Air leaks reduce effectiveness - ensure proper nasal prong sizing 5
• Insufficient humidification: Causes airway dryness and patient discomfort - maintain temperature at 37°C 5
• Failure to monitor continuously: HFNC patients are critically ill and require constant observation with immediate access to intubation capability 4

Advantages Over Conventional Oxygen Therapy

• More predictable FiO2 delivery: High flow prevents ambient air entrainment 8, 9
• Modest PEEP effect: Creates positive end-expiratory pressure of approximately 7 cm H2O at 50 L/min 1
• Superior patient comfort and tolerance: Better tolerated than face masks, can be worn during meals 1, 2
• Improved mucociliary clearance: Humidification and warming enhance secretion management 4, 8
• Reduced work of breathing: Upper airway flushing decreases respiratory effort 4, 8