From the Guidelines
There is no specific flow rate on high flow nasal cannula (HFNC) that universally requires patients to be NPO (nothing by mouth), and the decision should be individualized based on the patient's clinical condition, risk of aspiration, and respiratory status rather than the specific flow rate. The use of HFNC in acute respiratory failure has been gaining widespread use in hospitalized patients, with benefits including improved patient comfort and physiologic advantages, such as improved oxygenation and ventilation, better pulmonary compliance, reduced anatomical dead space, modest positive end-expiratory pressure, more efficient respiratory effort, reduced work of breathing, and secretion clearance 1. However, the effect of HFNC on clinical outcomes is not well established, and few clinical guidelines exist to provide clinicians with evidence-based recommendations on its appropriate use.
When considering oral intake in patients on HFNC, healthcare providers should assess the patient's risk of aspiration, respiratory status, and ability to safely swallow. Patients with severe respiratory distress, altered mental status, or those who are at high risk for aspiration may be kept NPO regardless of the HFNC flow rate. On the other hand, stable patients on HFNC who are alert, have intact airway protective reflexes, and can safely swallow may be allowed oral intake after careful assessment 1. The European Respiratory Society (ERS) has created a task force to provide evidence-based recommendations on HFNC in adults with acute respiratory failure, highlighting the importance of individualized decision-making in this context.
Key considerations for healthcare providers include:
- Performing bedside swallow evaluations when appropriate
- Monitoring patients closely during oral intake if it is deemed safe
- Reassessing the patient's ability to safely take oral intake if their respiratory status deteriorates or they show signs of increased work of breathing while on HFNC
- Weighing the benefits and risks of HFNC in different scenarios, such as hypoxaemic and hypercapnic acute respiratory failure, post-operative and post-extubation acute respiratory failure, and coronavirus disease 2019 (COVID-19) pneumonia 1.
From the Research
Flow Rates and NPO Status
- The ideal flow rate for high-flow nasal cannula (HFNC) therapy in patients who are NPO (nothing by mouth) is not explicitly stated in the provided studies.
- However, a study published in 2021 2 found that flow rates above 40 L/min were associated with an increased risk of aspiration and decreased swallowing function in healthy volunteers.
- Another study published in 2024 3 compared the outcomes of patients receiving HFNC at flow rates of 40 L/min and 60 L/min after extubation, but did not specifically address the issue of NPO status.
- A narrative review published in 2025 4 discussed the use of HFNC in patients with chronic obstructive pulmonary disease (COPD), but did not provide guidance on flow rates for NPO patients.
Clinical Considerations
- A study published in 2020 5 used HFNC therapy at flow rates up to 50-60 L/min in stroke patients with nasogastric intubation and obstructive sleep apnea, but this study did not address the specific question of NPO status.
- The same study found that only three out of 11 participants tolerated flow rates of 50-60 L/min for a one-week treatment period, suggesting that higher flow rates may not be well-tolerated by all patients.
- A clinical practice guideline published in 2020 6 provided recommendations for the use of HFNC in various clinical settings, but did not address the issue of NPO status or optimal flow rates for these patients.
Key Findings
- Flow rates above 40 L/min may be associated with an increased risk of aspiration and decreased swallowing function in healthy volunteers 2.
- Higher flow rates (60 L/min) did not reduce the risk of reintubation or noninvasive ventilation use compared to lower flow rates (40 L/min) in extubated patients 3.
- HFNC therapy may be effective in reducing the severity of obstructive sleep apnea in stroke patients with nasogastric intubation, but may not be well-tolerated by all patients 5.