High-flow nasal cannula: evolving practices and novel clinical and physiological insights

Roca, O., Li, J. & Mauri, T. High-flow nasal cannula: evolving practices and novel clinical and physiological insights. Intensive Care Med (2024). https://doi.org/10.1007/s00134-024-07386

High-Flow Nasal Cannula: Evolving Practices and Novel Clinical and Physiological Insights

Summary:

Latest Advances in Understanding the Physiological Effects of High-Flow Nasal Cannula: High-flow nasal cannula (HFNC) systems deliver heated and humidified gases at 30–60 L/min, improving carbon dioxide (CO2) clearance and achieving more stable alveolar oxygen fractions by reducing room-air entrainment. HFNC can generate a low positive end-expiratory pressure (PEEP), reducing respiratory drive, inspiratory effort, and minute ventilation. Factors like the interface, body position, and respiratory rate impact HFNC's efficiency. Asymmetrical prongs and awake-prone positioning enhance CO2 clearance and reduce lung strain.

HFNC in Acute Hypoxemic Respiratory Failure:

HFNC is indicated for hypoxemic patients who do not improve with conventional oxygen therapy, reducing intubation rates without affecting mortality. It can also be used post-extubation to decrease reintubation needs. Starting HFNC with an initial flow of 30–40 L/min, escalating as needed, is recommended. Patient comfort, influenced by HFNC temperature, is crucial for continuous administration.

HFNC in Acute and Chronic Hypercapnic Respiratory Failure:

HFNC is increasingly used for hypercapnic respiratory failure. Meta-analyses show no significant differences in intubation risk between HFNC and non-invasive ventilation (NIV) in acute hypercapnic respiratory failure. HFNC can be considered between NIV sessions or in cases of NIV intolerance. For stable hypercapnic COPD patients, HFNC may reduce moderate/severe exacerbations compared to conventional oxygen therapy.

The Importance of Detecting HFNC Failure:

Delayed intubation in HFNC-treated patients is associated with worse outcomes. Identifying HFNC failure through clinical assessment and physiological variables is crucial. The ROX index, measuring oxygen saturation/FiO2 to respiratory rate, is a reliable predictor of HFNC failure. Ongoing studies are exploring the use of ROX as a criterion for intubation.

HFNC Weaning:

Weaning HFNC is generally straightforward due to its non-invasive nature. Criteria for weaning include stability with respiratory rates ≤ 25 breaths/min and SpO2 ≥ 92% at 30 L/min flow and FiO2 0.4. Predictors of weaning success include FiO2 ≤ 0.4 and ROX ≥ 9.2. The sequence of reducing HFNC variables remains under investigation, with a general consensus to wean FiO2 first.

Take-Home Message:

HFNC offers benefits like improved oxygenation, CO2 clearance, reduced respiratory drive, and enhanced patient comfort, reshaping non-invasive respiratory support. Close monitoring and individualized therapy are essential to prevent adverse outcomes from delayed intubation. Future research should focus on refining weaning protocols, adjusting therapy variables, and understanding patient-specific responses.

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Watch this video on Asymmetrical Nasal High Flow for Noninvasive Respiratory Support by the American Physiological Society

Discussion Questions:

1. How can the implementation of asymmetrical prongs and awake-prone positioning enhance the effectiveness of HFNC therapy in hypoxemic patients?
2. What are the potential benefits and limitations of using the ROX index as a criterion for intubation in patients failing HFNC therapy?
3. How can future research improve the weaning process and therapy adjustment for HFNC to maximize patient outcomes and comfort?

Javier Amador-Castaneda, BHS, RRT, FCCM, CEO

Interprofessional Critical Care Network (ICCN)

[email protected]

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