The Edge: High-Flow Nasal Oxygen and EMS

Imagine a clinical system of noninvasive ventilation (NIV) that allows you to immediately intervene using the simplest technique (a nasal cannula) with a device that provides a patient in respiratory distress with the immediate support of CPAP in the posterior nasopharynx, a constant supply of oxygenated fresh gas independent of respiratory rate or minute ventilation, and quickly reduces their work of breathing. We’re talking about the newest and most versatile NIV system that has come to adult clinical medicine in the past 15 years: high-flow nasal oxygen.

An Intriguing Idea

High-flow nasal oxygen (HFNO) came to my awareness due to the innovative description of its use under the direction of Anil Patel, MD, at the 2016 meeting of the Society for Airway Management. Patel has utilized HFNO to maintain oxygenation and CO₂ removal in his patients under conditions of complete apnea for periods of over 15 minutes (100% FiO₂ with flows of 70 lpm) utilizing something that amounts to an oversize, beefed-up nasal cannula and heated humidification system. These operative procedures involved ENT airway laryngoscopies, and HFNO allowed the surgeons full unobstructed access to the airway without intervening tracheal tubes or jet ventilation catheters. Many of us were intrigued to investigate for our own practices. 

With fresh gas flows ranging between 40–70 lpm, HFNO functions through creating an area of turbulent gas flow in the posterior nasopharynx and immediate supraglottic area. This fresh gas flow has been demonstrated to improve oxygenation, maintain lung recruitment (through PEEP in the supraglottic region), facilitate passive removal of CO₂ from the respiratory system, and assist secretion clearance.  

In effect the patients are breathing and exchanging gas in an area directly above their larynx, with a degree of continuous positive pressure related to the flow of gas measured in one clinical study at 0.8 cm H₂O per 10 lpm gas flow.¹ A HFNO system at 40 lpm would generate 3.2 cm H₂O PEEP, and a HFNO system at 70 lpm would generate 5.6 cm H₂O PEEP in the immediate supraglottic anatomic position. The only contraindication to HFNO is suspected or actual skull base fracture.² 

HFNO represents a method of noninvasive ventilation that utilizes an appropriately sized nasal cannula apparatus fed by respiratory gas tubing with the approximate diameter of pediatric ventilator tubing. While commercial systems are available, medical professionals have utilized HFNO via improvised systems to great effect (e.g., ventilator systems set to high inspiratory flow and connected to large nasal cannula/supply tubing). Utilizing improvised HFNO systems requires an organization to acquire and maintain reliable and costly ventilator systems, as well as personnel at the critical care paramedic level. 

Benefits as a NIV System

Although it seems as if acquiring and using HFNO requires a lot of resources, it’s worth knowing about how it may assist prehospital care when the technology becomes simplified. For a thorough explanation, I will follow the template laid out in the article “A Systematic Review of the High-Flow Nasal Cannula for Adult Patients.”³ 

The simplicity of applying the HFNO system allows rapid and easy fitting and deployment. By applying the HFNO system to the patient, you avoid nonacceptance of a tight-fitting full-face mask by patients experiencing respiratory distress. Application of the HFNO “harness” is swift and easy, and the patient is rewarded immediately with a reduced work of breathing and a constant and even FiO₂. 

Tight-fitting face masks utilized with BiPAP systems are often complicated by mask fit and leak and on a long-term basis by injury to the skin and the inability of the patient to clear secretions. HFNO apparatus avoids the problems with proper fit and skin injury and allows clearance of secretions (and indeed, allows the patient to consume food and liquids while maintaining respiratory support). 

The HFNO modality has been found effective in managing patients with acute respiratory distress syndrome (including, recently, pneumonia from COVID-19 infection), respiratory compromise induced by heart failure, and respiratory failure following extubation and cessation of mechanical ventilation. A summary of three meta-analyses comparing HFNO to conventional supplemental oxygen therapy and BiPAP in patients experiencing acute hypoxemic respiratory failure demonstrated that mortality was unaffected (HFNO was noninferior to BiPAP), yet the HFNO was better tolerated by patients.³  

The potential to assist initiating invasive ventilation (tracheal intubation) is bolstered by the ability of the caregiver to remove the HFNO easily during face mask ventilation and reapply it during the tracheal intubation procedure, thereby administering the best possible apneic oxygenation. In a study comparing the efficacy of HFNO to bag-valve mask (BVM) during preoxygenation prior to tracheal intubation in patients with hypoxic respiratory failure, the patients managed with BVM technique experienced a more pronounced decrease in SpO₂ values at a greater rate than those managed with the HFNO method at the end of a one-minute apneic period.⁴ 

Summary

According to several friends and colleagues in critical care medicine, the use of HFNO has simplified the care of patients with moderate to severe COVID-19 infection by allowing those patients to avoid invasive ventilation. Furthermore, the process of utilizing prone positioning to improve oxygenation is greatly simplified when compared to the other method of NIV, namely BiPAP. The use of HFNO also functions independently of the presence of substantial facial hair, which often causes problems implementing NIV with a tight-fitting mask. HFNO has been demonstrated to be more effective than conventional oxygen therapy (nonrebreather mask), noninferior in most studies to other forms of NIV, and consistently better tolerated than tight-sealing face mask-based NIV approaches. 

Sidebar: Benefits of HFNO 

• Simplicity of application 
• Patient tolerance
• Speed of deployment
• Generation of PEEP in posterior hypopharynx 
• Reduction of anatomical dead space
• Improvement of mucociliary clearance (long-term use helps clear secretions)
• Reduced work of breathing
• Functions independently of presence of substantial facial hair
• Establishes and maintains lung recruitment due to application of PEEP
• Simple to apply and remove during face mask ventilation (in preparation for tracheal intubation)
• Applies apneic oxygenation during invasive airway management
• Noninferior to tight-fitting mask NIV in most studies
• Effective therapy for ARDS and respiratory compromise due to acute CHF

References

1. Groves N, Tobin A. High flow nasal oxygen generates positive airway pressure in adult volunteers. Aust Crit Care, 2007 Nov; 20(4): 126–31.

2. Hagberg C. Hagberg and Benumof’s Airway Management, 4th ed. Elsevier, 2017, p. 761.

3. Heviz Y, Einav S. Annual Update in Intensive Care and Emergency Medicine 2018. Springer, 2018, pp. 177–91.

4. Simon M, Wachs C, Braune S, et al. High-flow Nasal Cannula Versus Bag-Valve-Mask for Preoxygenation Before Intubation in Subjects With Hypoxemic Respiratory Failure. Respir Care, 2016 Sep; 61(9): 1,160–7. 

James “Jim” DuCanto, MD, is the associate medical director of airway and ventilation for FlightBridgeED, LLC. He recently accepted the position of medical director for Mid-State Technical College’s EMS program in Wisconsin Rapids, Wisc.