Why would a patient be on high-flow nasal cannula (HHFNC) instead of Continuous Positive Airway Pressure (CPAP) or Bi-level Positive Airway Pressure (BiPAP)?

Why a Patient Would Be on HFNC Instead of CPAP or BiPAP

HFNC is preferred over CPAP/BiPAP primarily for superior patient tolerance and comfort, which directly impacts treatment adherence and outcomes, particularly in patients with acute hypoxemic respiratory failure who need sustained respiratory support but cannot tolerate the tight-fitting interfaces required for noninvasive positive pressure ventilation. 1

Primary Clinical Advantages of HFNC

Patient Tolerance and Comfort

• HFNC significantly reduces patient discomfort compared to conventional oxygen therapy (standardized mean difference 0.54 lower, 95% CI 0.86 to 0.23 lower; high certainty), which translates to better sustained therapy 1
• HFNC avoids the claustrophobic sensation and skin breakdown associated with tight-fitting masks required for CPAP/BiPAP 1, 2
• The open interface allows patients to eat, drink, and communicate without interrupting therapy, which is impossible with CPAP/BiPAP masks 1, 3

Physiological Benefits Without Positive Pressure Complications

• HFNC provides low-level PEEP (typically 3-5 cmH2O) through high flow rates up to 60 L/min, which facilitates alveolar recruitment without the gastric insufflation and air leaks common with CPAP/BiPAP 1
• The therapy reduces anatomical dead space washout in upper airways, improving ventilation efficiency without requiring positive pressure 1, 3
• HFNC delivers reliable FiO2 up to 100% by matching inspiratory demands of dyspneic patients, preventing room air entrainment that occurs with lower flow systems 1

Specific Clinical Scenarios Favoring HFNC

Hypoxemic Respiratory Failure Without Hypercapnia

• HFNC may reduce intubation rates (risk ratio 0.89,95% CI 0.77 to 1.02) in acute hypoxemic respiratory failure, with similar mortality to conventional oxygen therapy 1
• The 2021 American College of Physicians guidelines recommend HFNC rather than NIV as first-line therapy for acute hypoxemic respiratory failure, with reduced intubation rates and lower mortality 4
• HFNC is most beneficial for patients at high risk of intubation with severe disease, rather than those requiring only low oxygen flow rates 1

Post-Operative Patients

• HFNC avoids the risk of anastomotic leakage and delayed wound healing that can occur with positive pressure from NIV/CPAP in surgical patients 1
• Post-operative patients show little difference in mortality or reintubation between HFNC and conventional oxygen therapy, but HFNC provides better comfort 1
• The increased mucociliary clearance from heated humidification is particularly valuable in post-operative patients prone to atelectasis 1

Post-Extubation Support

• HFNC is recommended over conventional oxygen therapy for adults developing respiratory failure after extubation, with reduced reintubation rates and improved patient comfort 4
• During breaks from respiratory support, HFNC can be used continuously whereas CPAP/BiPAP requires removal for patient activities 1

When CPAP/BiPAP Would Be Preferred Over HFNC

Hypercapnic Respiratory Failure

• NIV (CPAP/BiPAP) provides more aggressive ventilatory support through positive pressure, which is essential for CO2 elimination in hypercapnic patients 5
• HFNC has minimal effect on PaCO2 values (MD 0.01 mmHg, 95% CI -1.17 to 1.2 mmHg), making it inadequate for primary hypercapnic respiratory failure 1

Severe Hypoxemia Requiring Higher PEEP

• When patients require PEEP levels >5-7 cmH2O for adequate oxygenation, CPAP/BiPAP can deliver titrated positive pressure that HFNC cannot match 5
• NIV may provide more aggressive respiratory support through alveolar recruitment in severe ARDS 5

Obstructive Sleep Apnea or Upper Airway Obstruction

• CPAP/BiPAP provides consistent positive pressure to maintain airway patency, which HFNC cannot reliably achieve 3

Critical Monitoring Considerations

Signs HFNC May Be Insufficient

• Persistent tachypnea despite HFNC (respiratory rate >30 breaths/min after 1-2 hours) 5
• Worsening work of breathing with accessory muscle use 5
• SpO2/FiO2 ratio ≤150 mmHg within 1-2 hours indicates need for escalation to NIV or intubation 5
• Use validated prediction scores like HACOR scale to predict NIV failure within the first hour if escalating from HFNC 5

When to Escalate from HFNC

• If HFNC is not tolerated due to bloating or discomfort, first attempt flow rate reduction in 5-10 L/min increments while maintaining target oxygen saturation 6
• If respiratory status deteriorates despite optimized HFNC settings, trial NIV if no contraindications exist (inability to protect airway, hemodynamic instability, immediate deterioration) 5
• Proceed directly to intubation for severe hypoxemia with PaO2/FiO2 <100 mmHg despite optimized oxygen delivery 5

Common Pitfalls to Avoid

• Do not delay intubation in patients failing HFNC—NIV failure is an independent risk factor for mortality, and delayed intubation worsens outcomes 1
• Avoid using HFNC as primary therapy for hypercapnic respiratory failure where NIV is indicated 1, 5
• Do not assume HFNC provides equivalent positive pressure support to CPAP/BiPAP—the PEEP effect is minimal (3-5 cmH2O) 1, 3
• Monitor for aerophagia and gastric distension with HFNC, which can occur despite the open interface, particularly at flow rates >50 L/min 6