What is the role of high flow nasal cannula (HFNC) in managing acute respiratory failure?

Role of High-Flow Nasal Cannula in Acute Respiratory Failure

High-flow nasal cannula (HFNC) should be used as first-line therapy over conventional oxygen therapy in adults with acute hypoxaemic respiratory failure, and can be considered over noninvasive ventilation in most scenarios except for patients at high risk of extubation failure or those with hypercapnic COPD exacerbations. 1

Primary Indications for HFNC

Acute Hypoxaemic Respiratory Failure (De Novo)

HFNC is preferred over conventional oxygen therapy (COT) for acute hypoxaemic respiratory failure. 1 The evidence demonstrates:

• Reduced intubation rates (risk ratio 0.89,95% CI 0.77-1.02) and decreased need for escalation to NIV (risk ratio 0.76,95% CI 0.43-1.34) 1
• Similar mortality to COT at hospital discharge, ICU discharge, 28 days, and 90 days (risk ratio 0.99,95% CI 0.84-1.17 for short-term mortality) 1
• Significantly improved patient comfort and reduced dyspnoea (SMD 0.54 lower for discomfort, 95% CI 0.86 lower to 0.23 lower) 1
• Lower respiratory rate (mean difference 2.25 breaths/min lower, 95% CI 3.24-1.25 breaths/min lower) 1
• Better oxygenation with increased PaO₂ values (MD 16.72 mmHg higher, 95% CI 5.74-27.71 mmHg) 1

HFNC can also be used over NIV in hypoxaemic respiratory failure when NIV is not contraindicated, as the balance of effects appears favorable for patient tolerance and comfort. 1

Post-Extubation Respiratory Support

For patients at low or moderate risk of extubation failure, use HFNC over COT. 1 The evidence shows:

• Reduced reintubation rates (risk ratio 0.62,95% CI 0.38-1.01; risk difference −5.1%) 1
• Decreased need for NIV escalation (risk ratio 0.38,95% CI 0.17-0.85; risk difference −9.4%) 1
• No difference in mortality (risk ratio 1.01,95% CI 0.68-1.52) 1
• Improved comfort (SMD 0.77 SD) and reduced respiratory rate 1

However, for patients at HIGH risk of extubation failure, NIV should be used over HFNC unless contraindications to NIV exist. 1 High-risk patients include those with weak cough, poor neurological status, older age with severe cardiac or respiratory disease. 1

Post-Operative Respiratory Support

For post-operative patients at LOW risk of pulmonary complications, either HFNC or COT can be used. 1 The evidence shows minimal differences in mortality (risk ratio 0.64,95% CI 0.19-2.14), reintubation, or length of stay. 1

For post-operative patients at HIGH risk of pulmonary complications (especially after cardiothoracic or abdominal surgery), either HFNC or NIV can be used based on patient tolerance and surgical considerations. 1 Key considerations include:

• Risk of anastomotic leakage with positive pressure ventilation favors HFNC 1
• Skin breakdown is significantly more prevalent with NIV than HFNC after 24 hours 1
• Similar efficacy between HFNC and NIV for mortality and reintubation (though limited by imprecision) 1

When NOT to Use HFNC as First-Line

Hypercapnic COPD Exacerbations

Trial NIV before HFNC in patients with COPD and hypercapnic acute respiratory failure. 1 NIV has established mortality benefit in this population, whereas HFNC does not provide the same level of ventilatory support for CO₂ clearance. 1

High Risk of Extubation Failure

Use NIV over HFNC for patients at high risk of extubation failure (weak cough, poor neurological status, severe cardiac/respiratory disease, older age). 1 These patients require the superior ventilatory support that NIV provides. 1

Physiological Mechanisms Supporting HFNC Use

HFNC provides multiple physiological benefits that explain its clinical efficacy: 1, 2

• Matches high inspiratory demands with flows up to 60 L/min 1, 3
• Delivers reliable FiO₂ up to 100% 1
• Generates low-level PEEP in upper airways, facilitating alveolar recruitment 1
• Reduces anatomical dead space through CO₂ washout 2
• Provides heated and humidified gas (37°C, 100% relative humidity), improving mucociliary clearance 1, 3, 2
• Reduces work of breathing and inspiratory nasopharyngeal resistance 2

Critical Monitoring and Failure Recognition

Frequent reassessment is mandatory when using HFNC. 4 Signs of HFNC failure requiring escalation include:

• Severe end-organ dysfunction 4
• Thoracoabdominal asynchrony 4
• Significantly increased respiratory rate despite HFNC 4
• Poor oxygenation despite maximal HFNC settings 4
• Persistent tachycardia 4
• Higher SAPS II scores are associated with HFNC failure 5
• Additional organ failure, particularly hemodynamic or neurological 5

Delayed intubation in failing patients worsens mortality—do not persist with HFNC when clear failure criteria are present. 1

Practical Implementation

HFNC settings: 3

• Flow rates up to 60 L/min for adults 3
• Temperature: 37°C 2
• Humidification: 100% relative humidity 2
• FiO₂: titrate to target oxygenation 1

Liberation from HFNC: Use a stepwise approach similar to spontaneous breathing trials for mechanical ventilation, gradually reducing flow rate and FiO₂ when clinically appropriate. 6 Failure to de-escalate prolongs ICU/hospital length of stay and increases healthcare costs. 6

Resource and Safety Considerations

HFNC is well-tolerated, easy to use, and does not require specialized expertise unlike NIV. 2 Cost-effectiveness analyses suggest HFNC is likely cost-effective even in low-risk patients. 1

For infection control (relevant in COVID-19 and other respiratory infections): 4

• Use appropriate personal protective equipment 4
• Place surgical mask over HFNC device 4
• Ensure adequate room ventilation 4
• Adhere to hand hygiene protocols 4