What are the indications for heated high flow (HHF) therapy?

Indications for Heated High-Flow Nasal Cannula (HFNC) Therapy

Heated high-flow nasal cannula (HFNC) is indicated primarily for acute hypoxemic respiratory failure in adults, including pneumonia, ARDS, COVID-19, and post-extubation hypoxemia, where it reduces the need for intubation and improves oxygenation. 1

Primary Indications

Acute Hypoxemic Respiratory Failure

• HFNC is most effective in de novo acute hypoxemic respiratory failure, including pneumonia, acute respiratory distress syndrome (ARDS), and COVID-19, where it has demonstrated reduced intubation rates, shorter length of stay, and lower mortality in select conditions 1, 2
• Patients with severe hypoxemia despite conventional oxygen therapy who do not yet require intubation are ideal candidates 1
• HFNC provides reliable FiO2 delivery (up to 100%), generates positive end-expiratory pressure (PEEP), reduces anatomical dead space, and decreases work of breathing 1, 2

Immunocompromised States

• HFNC is indicated for immunocompromised patients with acute respiratory failure, where it may avoid the complications associated with invasive ventilation 1

Peri-Intubation and Post-Extubation

• HFNC is indicated for pre-oxygenation before intubation to maintain adequate oxygenation during the procedure 1, 3
• Post-extubation hypoxemia is an established indication, particularly in patients at high risk for reintubation 1, 3

Cardiogenic Pulmonary Edema

• While CPAP remains first-line for cardiogenic pulmonary edema with persistent hypoxia despite maximal medical treatment, HFNC may be considered when CPAP is not tolerated or available 4

Emerging and Secondary Indications

Chronic Obstructive Pulmonary Disease (COPD)

• HFNC shows emerging utility in acute hypercapnic exacerbations of COPD, particularly in patients intolerant to non-invasive ventilation (NIV) 5
• However, NIV remains the gold standard for COPD with respiratory acidosis (pH <7.35), and HFNC should be reserved for NIV-intolerant patients 4, 5
• Home high-flow therapy is under investigation for stable COPD but is not yet guideline-recommended 2, 6

Interstitial Lung Disease

• HFNC is indicated for acute exacerbations of interstitial lung disease with hypoxemic respiratory failure 1

Palliative Care

• HFNC provides effective symptom relief (dyspnea reduction) in patients with do-not-intubate orders or those receiving palliative respiratory care 1, 3

Procedural Support

• HFNC can be used during bronchoscopy to maintain oxygenation 3

Physiological Mechanisms Supporting Use

HFNC delivers several therapeutic benefits that justify its indications:

• Provides heated (37°C) and humidified (100% relative humidity) oxygen at flows up to 60 L/min, improving patient comfort and mucociliary clearance 1, 2
• Generates 3-5 cm H2O of positive end-expiratory pressure, which improves alveolar recruitment 2, 3
• Flushes nasopharyngeal dead space (approximately 150 mL), improving CO2 clearance 1, 2
• Reduces work of breathing by meeting or exceeding inspiratory flow demands 1, 2, 3

Critical Assessment and Monitoring Requirements

Predictors of HFNC Failure Requiring Escalation

Patients must be frequently reassessed for signs of HFNC failure, including:

• Severe end-organ dysfunction 1
• Thoracoabdominal asynchrony (paradoxical breathing) 1
• Persistently elevated respiratory rate (>30 breaths/min) despite HFNC 1
• Poor oxygenation despite maximal HFNC settings 1
• Tachycardia and hemodynamic instability 1

When HFNC Should NOT Be Used

• HFNC should not substitute for intubation when invasive ventilation is clearly more appropriate, such as in patients with impending respiratory arrest, severe hemodynamic instability, or inability to protect the airway 4
• Patients with chest wall trauma should be monitored in ICU settings if HFNC is used, due to pneumothorax risk 4
• In acute pneumonia with severe hypoxemia, HFNC trials should only occur in HDU or ICU settings with immediate intubation capability 4

Infection Control Considerations (COVID-19 Context)

• Appropriate personal protective equipment (PPE), hand hygiene, surgical mask placement over the HFNC device, and adequate room ventilation are essential to protect healthcare personnel from aerosolization risk 1
• Individual patient factors (severity of illness, cough frequency) should guide infection control measures 1

Common Pitfalls to Avoid

• Do not delay intubation in patients with clear indications for invasive ventilation while attempting HFNC therapy 4, 1
• Avoid using HFNC as a substitute for NIV in COPD with respiratory acidosis (pH <7.35), where NIV has superior evidence 4
• Do not use HFNC routinely in chest wall trauma; CPAP is preferred, and both require ICU monitoring 4
• Ensure arterial blood gas measurement in patients being considered for HFNC to guide appropriate respiratory support selection 4