What is the role of high flow oxygen therapy (HFOT) in adult respiratory failure?

High-Flow Oxygen Therapy in Adult Respiratory Failure

High-flow nasal oxygen (HFNO) should be used preferentially over noninvasive ventilation for initial management of acute hypoxemic respiratory failure and over conventional oxygen therapy for postextubation respiratory failure in hospitalized adults. 1

Primary Recommendations

Initial Management of Acute Hypoxemic Respiratory Failure

Use HFNO rather than noninvasive ventilation (NIV) as first-line therapy for adults with acute hypoxemic respiratory failure. 1 The American College of Physicians (2021) provides this as a conditional recommendation based on evidence showing:

• Reduced intubation rates compared to conventional oxygen therapy (risk ratio 0.60,95% CI 0.38-0.94) 2
• Lower mortality when compared to NIV in initial management 1
• Decreased hospital-acquired pneumonia risk versus NIV 1
• Superior patient comfort compared to NIV 1

Postextubation Respiratory Failure

Use HFNO rather than conventional oxygen therapy for adults developing respiratory failure after extubation. 1 This approach:

• Reduces reintubation rates compared to conventional oxygen 1
• Improves patient comfort significantly 1
• Provides better tolerance than NIV in the postextubation period 1

Mechanism and Physiologic Benefits

HFNO delivers warm (37°C), humidified oxygen at flows up to 60 L/min through small nasal cannulae. 1 The key physiologic advantages include:

• Reduced anatomical dead space through CO2 washout of upper airways 3
• Modest positive end-expiratory pressure (PEEP) effect in upper airways (low-level) 3
• Decreased work of breathing and more efficient respiratory effort 1
• Reliable FiO2 delivery up to 100% without ambient air dilution 3
• Enhanced mucociliary clearance through optimal humidification 1
• Reduced risk of patient self-inflicted lung injury (P-SILI) 3

Target Oxygen Saturation

Maintain SaO2 of 88-92% in all causes of acute hypoxemic respiratory failure. 3 This target prevents hyperoxygenation, which can be harmful in patients with respiratory failure. 3

Clinical Implementation Algorithm

Step 1: Initial Setup

• Start HFNO at flow rates of 50-60 L/min 3
• Set FiO2 to achieve target SaO2 88-92% 3
• Position patient with head of bed elevated 30-45 degrees 4
• Ensure proper nasal cannula fit and encourage mouth closure to optimize airway pressure effects 4

Step 2: Monitoring Requirements

Continuous monitoring is mandatory as these patients remain critically ill: 5

• Continuous oxygen saturation monitoring 3
• Intermittent pCO2 and pH measurement 3
• ECG monitoring if pulse rate >120 bpm or dysrhythmia present 3
• Frequent reassessment for signs of HFNO failure 6

Step 3: Identifying HFNO Failure

Escalate to invasive mechanical ventilation if any of the following develop: 6

• Severe end-organ dysfunction
• Thoracoabdominal asynchrony
• Significantly increased respiratory rate despite HFNO
• Poor oxygenation despite maximal HFNO settings
• Persistent tachycardia
• Worsening work of breathing

Comparison with Alternative Therapies

HFNO vs. Conventional Oxygen Therapy

HFNO demonstrates clear superiority: 1, 2

• Lower intubation rates (RR 0.60)
• Reduced need for escalation to more invasive support (RR 0.89) 3
• Decreased dyspnea and patient discomfort 3
• Similar mortality in short-term and at 90 days 3

HFNO vs. Noninvasive Ventilation

For initial acute hypoxemic respiratory failure management, HFNO offers: 1

• Similar or lower intubation rates (RR 0.86,95% CI 0.68-1.09) 2
• Better patient tolerance and comfort 1
• Fewer complications including reduced hospital-acquired pneumonia 1
• Easier to use across all clinical settings without requiring specialized expertise 7

Important Clinical Caveats

Hypercapnic Respiratory Failure

Do not use HFNO as first-line therapy in hypercapnic respiratory failure. 5 The data remain inconclusive for this indication, and NIV should be preferred in patients with elevated CO2 levels. 5

Infection Control Considerations

HFNO does not increase aerosol formation compared to conventional oxygen therapy and can be safely used in COVID-19 patients. 5 Essential precautions include:

• Appropriate personal protective equipment 6
• Surgical mask placement over the HFNC device 6
• Adequate room ventilation 6
• Strict hand hygiene adherence 6

Managing Bloating and Aerophagia

The PEEP effect can cause gastric distension: 4

• Titrate flow rates downward in 5-10 L/min increments if bloating occurs 4
• Monitor oxygen saturation during adjustments to ensure it remains in target range 4
• Consider smaller, more frequent meals 4
• Use anti-gas medications (simethicone) if bloating persists 4
• Reassess comfort 30-60 minutes after adjustments 4

When to Consider Alternatives

If bloating significantly impacts patient comfort or nutrition despite adjustments, consider conventional oxygen therapy if respiratory status allows, or NIV if at high risk of extubation failure without contraindications. 4

Evidence Quality and Strength

The 2021 ACP guidelines represent the most recent high-quality evidence, based on systematic review of 29 randomized controlled trials through February 2021. 1 However, recommendations are conditional with low-certainty evidence due to:

• Variation in trial populations and ARF etiologies 1
• Inadequate sample sizes and follow-up duration in many trials 1
• Poor characterization of protocols and resource requirements 1

Despite these limitations, the consistency of benefit across multiple outcomes and superior patient tolerance support HFNO as the preferred initial approach for acute hypoxemic respiratory failure. 1