Written by: Jordan Maivelett, MD (EM Resident Physician, PGY-1, NUEM); Edited by: Bill Burns, MD (EM Resident Physician, PGY-4, NUEM); Expert Commentary by: Jacqueline Kruser, MD
High flow nasal cannula (HFNC) is a method of oxygen delivery that can administer oxygen at flow rates of up to 60 L/min with fractions of inspired oxygen between 0.21 and 1.0 . The main proposed benefit of HFNC is improved oxygenation when compared with standard oxygen therapy. This is achieved through a variety of mechanisms, including:
- Dead space washout
- Positive end expiratory pressure effect that increases alveolar recruitment
- Matching the high inspiratory flow rates in acute respiratory failure to decrease dilution of inhaled oxygen by room air [2,3].
The delivered gas is often heated and humidified to prevent mucosal dehydration, maintain mucociliary function, and reduce heat loss [1,3].
HFNC is increasing in popularity in multiple clinical environments despite limited evidence regarding its use, and the effects of HFNC on patient outcomes are still being studied. For the emergency physician, HFNC is a potential tool to be utilized in acute respiratory distress, but is there data to support the use of HFNC for acute respiratory distress in the emergency department (ED)?
A recent meta-analysis by Monro-Somerville et al examined the use of HFNC compared with standard oxygen therapy or noninvasive ventilation (NIV), such as CPAP, in adult patients . The analysis included nine trials totaling 2507 patients. The majority of the trials were in the ICU or postoperative setting, with two trials specifically set in the ED. The study showed no statistical difference in hospital mortality or intubation rate when comparing HFNC with usual care. Notably, the authors conducted a subgroup analysis comparing the intubation rates between HFNC vs. standard oxygen therapy (e.g., nasal cannula) and HFNC vs. NIV. In this subgroup analysis, there was a significantly lower intubation rate in the HFNC group compared with standard oxygen therapy. There was no difference in intubation rate between HFNC and NIV .
All nine trials examined HFNC’s effects on dyspnea and comfort scores, with specific scoring systems and results varying between trials. Four studies showed significantly decreased dyspnea scores with HFNC use compared with standard oxygen therapy, four studies showed no difference, and one actually favored standard oxygen therapy over HFNC for dyspnea score reduction . Five studies showed significantly improved comfort when using HFNC vs. standard oxygen therapy or NIV, while other studies showed no difference.
Frat et al, one of the largest studies included in the above meta-analysis, was a randomized controlled trial of 310 patients which showed a potential benefit of HFNC in one specific patient population: Isolated acute hypoxemic respiratory failure . This study was conducted in the ICU setting and excluded patients with hypercapnea, cardiogenic pulmonary edema, known chronic lung disease, or acute asthma exacerbations. Their strict inclusion and exclusion criteria resulted in a study population with isolated acute hypoxemic respiratory failure, largely due to pneumonia. The trial compared the use of HFNC, standard oxygen therapy, and NIV. Results showed no difference in intubation rate between groups, though there was a statistically significant reduction in 90-day mortality in the HFNC group compared with standard oxygen therapy or NIV . The external validity of these results is limited given the strict inclusion and exclusion criteria, particularly when trying to apply them to the ED setting where patients with acute respiratory distress are undifferentiated. However, it is worth noting that based on these results there appears to be a mortality benefit for HFNC use in patients with acute isolated hypoxemic respiratory failure due to pneumonia.
Few studies have actually looked at the use of HFNC specifically in the emergency department. Similar to studies in the ICU and postoperative settings, results are mixed. The HOT-ER study, a trial included in the aforementioned meta-analysis by Monro-Somerville et al, was a randomized controlled trial examining the use of HFNC for acute respiratory distress in a tertiary academic ED. This trial compared HFNC with standard oxygen therapy (e.g., nasal cannula) in 322 patients . The study showed that significantly fewer patients treated with HFNC required mechanical ventilation within the first 24 hours after admission compared with standard oxygen therapy . However, there was no statistical difference between therapies regarding conversion to NIV in the ED, intubation in the ED, ED length of stay, ICU admission rate, hospital length of stay, in-hospital mortality, or 90-day mortality. There was no difference in adverse events between therapies .
Another ED specific randomized controlled trial comparing HFNC with standard oxygen therapy for acute respiratory distress in 100 patients found a statistically significant reduction in respiratory rate, decreased need for escalation of ventilation therapy, and lower self reported Borg scores of physical exertion in the HFNC group . Similar to the HOT-ER study, there was no difference in ED length of stay or ICU admission rate between groups. Mortality was not studied.
A smaller ED study conducted by Rittayamai et al in 40 patients showed lower dyspnea scores and improved comfort scores in the HFNC group compared with standard oxygen therapy . Mortality and intubation rate were not studied.
Overall, the data regarding HFNC use in the ED for acute respiratory distress is mixed, with possible benefits including improved symptom control and potential decrease in need for escalation to NIV or intubation. However, disposition and mortality do not appear to be affected based on the current data, and the sample sizes in these studies may not provide sufficient power to truly comment on HFNC’s effects.
- HFNC appears to be as safe and effective as standard therapy
- HFNC appears to improve patient comfort and reduce dyspnea
- Meta-analysis of HFNC suggests no difference between HFNC and standard care in mortality or intubation rate, though intubation data was mixed.
- HFNC has a mortality benefit in a specific patient population – isolated acute hypoxemic respiratory failure due to pneumonia
- ED specific studies are limited. Based on available data, disposition and mortality appear unaffected.
This is an excellent review of the current evidence evaluating the use of high flow nasal cannula (HFNC) for critically ill patients. HFNC is a relatively new form of supportive care available in emergency departments and intensive care units, and there has been a growing interest in examining its influence on patient outcomes. To put this literature review in context, it might be helpful to recall the basics of hypoxemic respiratory failure and how HFNC is related to our standard tools for supplemental oxygen delivery.
Patients who may benefit from HFNC
A patient who has or is at risk for tissue hypoxia (usually due to critical illness)
- There are 3 components to maintain tissue oxygenation:
- Gas exchange
- Circulatory distribution
- HFNC is used to improve gas exchange
- Poor gas exchange (aka hypoxemic respiratory failure) is manifested by arterial hypoxemia
Pitfalls and Contraindications for HFNC
- HFNC is good for patients who have isolated hypoxemic respiratory failure
- In general, HFNC is not used in hypoventilatory (hypercarbic) respiratory failure (although there is ongoing research examining this indication).
- Use common sense and do not delay intubation for a trial of HFNC in patients with hypoxemic respiratory failure who also have another indication for intubation:
- Lack of airway patency
- Inability to protect airway from aspiration
- Ventilatory respiratory failure
- Likely or impending clinical deterioration that will eventually lead to intubation
Other potential uses of HFNC
- Pre-intubation/ denitrogenation
- Post cardiac surgery
- During invasive procedures with moderate sedation
- Sleep apnea and other patients with sleep-disordered breathing
- Comfort care near end of life
Supplemental oxygen delivery in hypoxemic respiratory failure: Why HFNC works
- Basic principal of oxygen supplementation: Fully saturate hemoglobin and maximize dissolved oxygen in plasma
- How? increase the fraction of inspired oxygen (FiO2)
- Typical options: nasal cannula, simple face mask, non-rebreathing reservoir mask, venturi mask
- The concentration of oxygen delivered to the patient’s lungs depends on 2 things:
- The oxygen flow rate (or the available reservoir of 100% oxygen)
- The patient’s minute ventilation
- For any given oxygen flow rate or oxygen reservoir, the FiO2 will decrease as the patient’s minute ventilation increases (e.g. the faster the respiratory rate and the larger the patient’s tidal volume, the more room air is entrained and the amount of oxygen delivered to the lungs is decreased). This does not apply for invasive ventilation or non-invasive ventilation with an adequate mask seal.
- To increase the FiO2 delivered to a patient with a high minute ventilation, it is necessary to increase the oxygen flow rate or oxygen reservoir.
- HFNC works because the extreme flow rates (up to 60 liters per minute) generated by the system can match the inspiratory flow demand from the patient and create an “infinite reservoir” of oxygen.
Other ancillary effects and benefits of HFNC:
- Minimal amounts of positive end-expiratory pressure: 1 to 5 cwp PEEP
- Maximum of ~2 cwp if the patient’s mouth is open
- Not considered “positive-pressure ventilation”
- HFNC is an open circuit and relies on patients’ spontaneous efforts to generate tidal volumes
- Anatomical dead space wash out of CO2
- Heated, humidified air to maintain mucociliary clearance
- Patient comfort
- Possible hemodynamic effects in physiologic studies: Reduction in RV preload
Take Home Points:
- This literature review provides an excellent summary of the current evidence for the use of HFNC for acute, hypoxemic respiratory failure.
- Overall, the bulk of the existing evidence suggests that HFNC is safe and is not inferior to conventional oxygen therapy or non-invasive positive-pressure ventilation for acute, hypoxemic respiratory failure.
- Many practical features of HFNC make it very easily adopted and tolerated in real-world patient care settings, including the emergency department.
- The largest, multi-center, randomized study to date (FLORALI study by Frat et al.) suggests a mortality benefit to HFNC in patients with acute hypoxemic respiratory failure, which may be conferred through a decreased intubation rate in the subgroup of patients with the most severe hypoxemia (PaO2:FiO2 < 200).
- The largest trial of HFNC specific to the ED (HOT-ER study by Jones et al.) included patients with both hypoxemic and hypercarbic respiratory failure, which limits our ability to draw conclusions and compare to non-ED trials with more homogenous patient groups (e.g. hypoxemic respiratory failure).
- HFNC has already become a mainstay of supportive care for patients with hypoxemic respiratory failure, and its clinical applications will likely continue to grow over time.
Important questions remain about how to improve the use of HFNC in our patients:
- How can we establish and titrate the optimal flow rate to individualize patient therapy?
- What patient subgroups will have the most benefit from this therapy?
- Can we establish early predictors of HFNC failure to prevent unnecessary delay in intubation
- Does early initiation of HFNC in the emergency department for patients with isolated, hypoxemic respiratory failure improve hospital and long-term patient outcomes?
Jacqueline Kruser, MD
Pulmonary Critical Care Fellow, Northwestern Memorial Hospital
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How To Cite This Blog Post
[Peer-Reviewed, Web Publication] Maivellet J, Burns B (2017, May 2). Is High Flow Nasal Cannula Effective for Adults with Acute Respiratory Distress in the Emergency Department? [NUEM Blog. Expert Commentary By Kruser J]. Retrieved from http://www.nuemblog.com/blog/high-flow
- Jones et al. “Randomized Controlled Trial of Humidified High-Flow Nasal Oxygen for Acute Respiratory Distress in the Emergency Department: The HOT-ER Study.” Respir Care 2016; 61(3):291-299
- Roca et al. “Current evidence for the effectiveness of heated and humidified high flow nasal cannula supportive therapy in adult patients with respiratory failure.” Critical Care 2016; 20:109.
- Monro-Somerville et al. “The Effect of High-Flow Nasal Cannula Oxygen Therapy on Mortality and Intubation Rate in Acute Respiratory Failure: A Systematic Review and Meta-Analysis.” Crit Care Med 2016; Epub ahead of print.
- Frat et al. “High-Flow Oxygen through Nasal Cannula in Acute Hypoxemic Respiratory Failure.” N Engl J Med 2015; 372:23.
- Bell et al. “Randomised control trial of humidified high flow nasal cannulae versus standard oxygen in the emergency department.” Emerg Med Australia 2015; 27:537-541. Rittayamai et al. “Use of High-Flow Nasal Cannula for Acute Dyspnea and Hypoxemia in the Emergency Department.” Resp Care 2015; 60(10)