Is asymmetrical high flow nasal cannula (HFNC) better tolerated than conventional high flow nasal cannula (HFNC)?

From the Guidelines

Asymmetrical high flow nasal cannula (HFNC) is not proven to be better tolerated than conventional HFNC, and conventional HFNC remains the standard of care due to its established benefits and lack of strong evidence supporting asymmetrical designs. While some studies suggest that HFNC, in general, is better tolerated and more comfortable than conventional oxygen therapy, such as face masks [ 1 ], there is no specific evidence provided to support the use of asymmetrical HFNC over conventional HFNC. Conventional HFNC has been shown to be effective in delivering high-concentration oxygen therapy, providing a CPAP effect, and improving patient comfort compared to face masks [ 1 ]. The key factors influencing patient tolerance of HFNC include flow rate, temperature, FiO2 settings, proper sizing of the nasal prongs, and individual patient characteristics.

Key Considerations for HFNC Therapy

• Flow rate: Typically 20-60 L/min, with the ability to accommodate at least 60 L/min via standard dimension prongs on adult nasal cannula [ 1 ].
• Temperature: Usually 31-37°C.
• FiO2 settings: 21-100%.
• Proper sizing of the nasal prongs is crucial for patient comfort and effectiveness of the therapy.
• Individual patient characteristics, such as the need for high-concentration oxygen therapy or the presence of respiratory failure, play a significant role in determining the tolerance and success of HFNC therapy.

Evidence Supporting Conventional HFNC

Studies have demonstrated the effectiveness and tolerability of conventional HFNC in various clinical settings. For example, a prospective randomized trial by Tiruvoipati et al., as mentioned in [ 1 ], showed HFNC to be as effective as high-flow face mask in delivering oxygen to extubated patients, with a significant difference in tolerance of HFNC. Another study by Hernández et al., also referenced in [ 1 ], found that the use of HFNC oxygen compared with conventional oxygen therapy reduced the risk of reintubation within 72 hours in mechanically ventilated patients at low risk of reintubation.

Given the current state of evidence, the focus should remain on optimizing conventional HFNC parameters for individual patients rather than adopting asymmetrical designs without strong supporting evidence. This approach ensures that patients receive the most effective and comfortable oxygen therapy based on the best available research.

From the Research

Asymmetrical High Flow Nasal Cannula (HFNC) Tolerance

• The study 2 found that asymmetrical HFNC support slightly improved patient comfort without affecting lung aeration, diaphragm activity, ventilatory efficiency, dyspnea, and gas exchange in post-extubation hypoxemic acute respiratory failure.
• Another study 3 suggested that the asymmetrical cannula performed similarly to the standard cannula in terms of diaphragm activity, dyspnea, and patient's comfort in COPD hypercapnic patients.
• However, the study 2 reported that comfort was greater during asymmetrical HFNC support, with a median comfort score of 10 [7-10] compared to 8 [7-9] for the standard interface (p-value 0.044).
• The study 4 also found that HFNC was associated with superior comfort and patient tolerance compared to NIV or COT in patients with acute hypoxemic respiratory failure.

Comparison of Asymmetrical and Conventional HFNC

• The study 2 compared the effects of asymmetrical HFNC and standard HFNC on lung aeration, diaphragm activity, ventilatory efficiency, gas exchange, dyspnea, and comfort in post-extubation hypoxemic acute respiratory failure, and found no significant differences.
• The study 3 found that the asymmetrical cannula did not significantly decrease PaCO2 compared with the standard cannula in COPD hypercapnic patients.
• However, the study 3 also found that the asymmetric NHF cannula performed significantly better in reducing the dead space ventilation and increasing the ventilatory efficiency in more advanced COPD patients with more severe hypercapnia.

Clinical Implications

• The study 2 suggested that the use of asymmetrical HFNC may be a viable option for patients with post-extubation hypoxemic acute respiratory failure, as it provides similar performance to standard HFNC with improved patient comfort.
• The study 4 suggested that HFNC may be superior to COT in AHRF patients in terms of oxygenation, patient comfort, and work of breathing, and may be considered as an intermediate level of oxygen therapy between COT and NIV.
• The study 3 suggested that the asymmetric NHF cannula may be beneficial in reducing dead space ventilation and increasing ventilatory efficiency in advanced COPD patients with severe hypercapnia.