How to set up a high flow nasal cannula (HFNC) for a patient with a history of respiratory issues?

How to Set Up High Flow Nasal Cannula (HFNC)

Start with a flow rate of 40-50 L/min, temperature of 37°C, and titrate FiO2 to achieve target SpO2 of 94-98% (or 88-92% in patients at risk for hypercapnia), then adjust flow in 5-10 L/min increments based on patient comfort and work of breathing. 1

Initial Settings

Flow Rate

• Begin with 40-50 L/min for most adults with acute hypoxemic respiratory failure 1
• For more severe hypoxemia (PaO2/FiO2 ≤200 mmHg), start at the higher end: 50-60 L/min to maximize PEEP effect and dead space washout 1, 2
• Maximum flow capacity is 60 L/min for adults 1, 2
• For post-extubation support, 35-50 L/min is typically sufficient 1

Temperature

• Set temperature to 37°C initially for optimal humidification 1
• Important caveat: While 37°C provides best humidification, research shows patients often report greater comfort at 31°C, particularly at lower severity of illness 3
• Adjust temperature between 34-37°C based on patient preference, with more severely hypoxemic patients (FiO2 ≥45%) tolerating higher temperatures better 1, 3

FiO2 (Fraction of Inspired Oxygen)

• Titrate FiO2 to achieve SpO2 94-98% for patients without risk of hypercapnia 1
• For patients at risk of hypercapnic respiratory failure (COPD, obesity hypoventilation): target SpO2 88-92% 1, 4
• Adjust in 5-10% increments to maintain target saturation 1

Monitoring and Assessment (Critical Within First Hour)

Immediate Reassessment (30-60 Minutes)

• Reassess within 30-60 minutes after initiating HFNC to evaluate response 2, 4
• Monitor respiratory rate—it should decrease with effective therapy 1
• Assess work of breathing for accessory muscle use 1
• Continuous pulse oximetry monitoring 1
• Check arterial blood gases when necessary to assess PaCO2 and PaO2/FiO2 ratio 1

Red Flags for HFNC Failure (Escalate Immediately)

• No improvement in respiratory rate or work of breathing within 1-2 hours 2
• Rapid shallow breathing index (RSBI) >105 breaths/min/L 2
• Tidal volumes persistently >9.5 mL/kg predicted body weight 2
• Development of altered mental status or inability to protect airway 2
• Progressive respiratory distress despite maximal HFNC settings 2

Titration Algorithm

Flow Rate Adjustments

• Increase by 5-10 L/min if increased work of breathing, persistent tachypnea, or worsening hypoxemia 1
• Decrease by 5-10 L/min if patient reports discomfort, nasal dryness, or difficulty exhaling 1, 5
• Higher flows (50-60 L/min) provide greater physiological benefit but some patients cannot tolerate flows above 40-50 L/min despite theoretical advantage 1, 2

FiO2 Adjustments

• Titrate in 5-10% increments to maintain target SpO2 1
• Avoid excessive oxygen (FiO2 >60% prolonged) due to risk of oxygen toxicity 1
• Wean FiO2 first before reducing flow rate once patient stabilizes 1

Special Clinical Contexts

Hypoxemic Respiratory Failure

• Use higher initial flows: 50-60 L/min 1, 2
• Target SpO2 94-98% 1
• HFNC is preferred first-line over conventional oxygen therapy 6, 2

COPD/Hypercapnic Respiratory Failure

• Try NIV first—it remains the preferred modality 4
• If NIV not tolerated, use HFNC at 35-60 L/min with lower SpO2 targets (88-92%) 1, 4
• Monitor PaCO2 closely as HFNC has lower ability to unload respiratory muscles compared to NIV 2, 4

Post-Extubation

• Flow rates of 35-50 L/min are typically sufficient 1
• For high-risk extubation patients, NIV is preferred over HFNC unless contraindications exist 2
• HFNC can be used during breaks from NIV 6, 2

Post-Operative (Cardiac/Thoracic Surgery)

• Either HFNC or conventional oxygen therapy is reasonable for low-risk patients 6
• For high-risk patients, either HFNC or NIV can be used 6
• HFNC may be preferred when positive pressure NIV risks anastomotic leakage 6

Critical Pitfalls to Avoid

Delayed Escalation

• Most dangerous error: Prolonging inadequate HFNC support when patient is failing leads to delayed intubation and increased mortality 2, 4
• Escalate to NIV or intubation promptly if no substantial improvement within 1-2 hours 2, 4

Inadequate Flow Rate

• Flows below therapeutic threshold provide insufficient PEEP effect and dead space washout 1
• For adults, ensure flow is truly "high flow" (≥30 L/min minimum, ideally 40-60 L/min) 1, 2

Poor Interface Fit

• Air leaks reduce effectiveness—ensure proper nasal cannula sizing 1
• Cannula diameter affects both pressure generation and comfort: larger diameter (5mm) generates more pressure but may cause discomfort with expiration 5

Insufficient Humidification

• Always use heated humidification to prevent airway dryness 1, 7
• Temperature too low (<34°C) provides inadequate humidification 1

Wrong Patient Selection

• Do not use HFNC in patients requiring immediate intubation: severe hemodynamic instability, depressed mental status, inability to protect airway, multi-organ failure, or severe facial/skull base trauma 2
• In COPD with hypercapnic respiratory failure, NIV should be attempted first 4