Use of high-flow nasal cannula oxygen therapy in infants and children

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What is HHHFNC oxygen?

Heated, humidified high-flow nasal cannula (HHHFNC) oxygen therapy provides warmed, humidified oxygen at flow rates that exceed minute volume requirements. Flow rates of 1 L/kg/min to 2 L/kg/min can deliver high oxygen concentrations and some degree of positive intrathoracic airway pressure [1]. Since its introduction to neonatal intensive care over 20 years ago [2], HHHFNC therapy has been used increasingly for support of neonates, children and adults with severe respiratory distress and to avoid the need for intubation or reintubation [3][4].

How does HHHFNC oxygen work?

HHHFNC oxygen therapy minimizes or eliminates the inspiration of room air (and the subsequent dilution of supplemental high fraction of inspired oxygen [FiO2] gas) that occurs during low-flow oxygen therapy, using supplemental gas flow rates that ‘wash out’ anatomic dead space. Efficient humidification and heating by commercial high-flow devices allows gas to flow at rates that would not be well tolerated or comfortable for patients, were they delivered by other means. Compared with continuous positive airway pressure (CPAP), which delivers gas flow at changing rates to maintain constant and positive intrathoracic pressure during inspiration and expiration, HHHFNC provides a constant, steady flow of gas. Airway pressures vary with inspiration and exhalation because the delivered gas flow is unchanging. HHHFNC oxygen therapy provides some degree of positive nasopharyngeal and intrathoracic pressure during exhalation, and usually only when higher gas flows (approximately 2 L/kg/min) are administered [5]. Both upper and lower airway resistance are reduced significantly by using high-flow therapy [5].

What are the benefits?

While low-flow oxygen therapy can only deliver high concentrations of oxygen to neonates, HHHFNC can deliver 100% O2 to older children and adults and is well-tolerated [6][7]. Washout of anatomic dead space in the upper and intrathoracic airways reduces work of breathing [5]. While paediatric studies have not demonstrated decreased partial pressure of carbon dioxide (PaCO2) levels with the use of HHHFNC, respiratory rates and work of breathing are reduced, suggesting that improved minute ventilation and CO2 clearance are occurring [5][8]. Extensive neonatal literature exists to support the role of this therapy in reducing need for invasive ventilation and intubation specifically [9]. Most paediatric (i.e., non-neonatal) studies have focused on infants or young children with bronchiolitis or pneumonia [10][11]. Limited pre- and post-intervention studies have suggested reduced need for intubation with HHHFNC use but were not powered to demonstrate reduced mortality or shorter stays in intensive care [12]-[14]. Observational data (case series) have suggested a potential role for this therapy in young patients with upper airway obstruction or neuromuscular disease and in older children with asthma or pneumonia, although the data for all these conditions are limited [13]-[15]. Some data have also suggested that children with congestive heart failure may benefit from HHHFNC, possibly because of its effects on reducing systemic afterload and preload [16] (Table 1).

How to use HHHFNC

For HHHFNC therapy to be effective and safe, medical gases must be adequately heated and humidified. A high-flow delivery of dry gas can irritate airways, activate bronchospasm and thicken or dry out respiratory and nasopharyngeal secretions. Circuit-size must be large enough to minimize resistance to gas flow, and nasal cannulae must be small enough to fit but not obstruct the patient’s nostrils. Cannulae that are too big or excessive nasal secretions can lead to increased intrathoracic pressure in patients who cannot open their mouths to relieve pressure at higher gas flows. Commercial paediatric devices either have a pressure relief valve built into the circuit or are designed to sense excessive circuit pressure and reduce gas flow accordingly (“cycling off”). Adult commercial circuits do not have these safety features and depend upon the patient’s ability to relieve rising nasopharyngeal or airway pressures by mouth-opening. Choice of circuit and cannula size should be patient-specific and fully accord with individual manufacturer specifications. Local respiratory therapy personnel usually are trained to make these decisions and assist the practitioner as required.

When initiating HHHFNC therapy, set the start flow at 1 L/kg/min to 2 L/kg/min and escalate as needed to minimize work of breathing (e.g., retractions, tachypnea, grunting, nasal flaring). The maximum flow rate should be 2 L/kg/min, with an upper limit of 50 L/min to 60 L/min for adult-sized patients. Commonly, oxygen concentration is started at an FiO2 of 50% and titrated up (or down) as needed to achieve a target oxygen saturation of 94% to 98% [1][4]. As work of breathing improves, flow rate can then be slowly titrated down. The FiO2 for delivered gas should be reduced based on oxygen saturation and determined independently of the titrated flow rate. When patients can tolerate a lower gas flow rate and FiO2, they can be switched to low-flow O2 respiratory support. Duration of therapy is determined by the disease course (which can take hours to weeks, depending on the case). Remember that initiating HHHFNC therapy worsens respiratory distress in some patients, due to breath-stacking or auto-PEEP. In such cases, work of breathing may actually improve with a reduction in flow rate.

Safety considerations

Clinicians must remember that although HHHFNC therapy can dramatically improve patient status, high-risk cases often need escalated care and support, including intubation and positive-pressure ventilation. Acutely unwell patients require careful observation and monitoring and frequent respiratory assessment in a setting where rapid airway support is always accessible. Institutional protocols that include a nursing staff-to-respiratory therapist ratio should be established and reviewed in practice to ensure that HHHFNC therapy use on site is appropriate, effective and safe.

Not all patients improve with HHHFNC therapy and such cases often require positive-pressure ventilation and ICU support. Non-responders may already have an elevated PaCO2 before starting HHHFNC therapy, with severe tachypnea or failure to improve over the first several hour(s) of treatment [13][17]-[19]. Excessive gas flow rates can impede exhalation in some patients with increased airway resistance. Higher intrathoracic pressures can reduce preload or increase pulmonary ventricular afterload, leading to hemodynamic instability, especially in patients who are hypovolemic. HHHFNC therapy is contraindicated in the setting of nasal obstruction, epistaxis and severe upper airway obstruction. Case reports exist of air-leak syndrome (i.e., pneumothorax) or abdominal distention (due to swallowing of gas) with use of HHHFNC therapy, but they are rare and causality is unclear [20]. Complications from ‘third-spacing’ of air can also occur when HHHFNC therapy is administered to patients with facial trauma or following upper airway or esophageal surgery. A sudden discontinuation or failure of HHHFNC therapy can precipitate a rapid deterioration in respiratory status and hemodynamics, necessitating the care of such cases in closely monitored settings.

In the transport setting, both reported clinical experience with HHHFNC therapy and availability of approved HHHFNC devices are limited. Patients needing transfer for different or higher levels of care might not tolerate transitioning back to low-flow oxygen therapy, and may require additional respiratory support (e.g., intubation or bilevel positive airway pressure [BiPAP]) to ensure safe transport. This risk should be taken into account when HHHFNC therapy is being considered or initiated in settings without immediate access to on-site critical care support. Early discussion with local medical transport resources will inform whether HHHFNC is a reasonable transport option for the individual patient.

Acknowledgements

This practice point was reviewed by the Community Paediatrics Committee and Respiratory Section of the Canadian Paediatric Society.

CANADIAN PAEDIATIC SOCIETY ACUTE CARE COMMITTEE

Members: Carolyn Beck MD, Laurel Chauvin-Kimoff MD (Chair), Kimberly Dow MD (Board Representative), Catherine Farrell MD (past member), Evelyne D. Trottier MD, Kristina Krmpotic MD, Kyle McKenzie MD

Liaisons: Kevin Chan MD, CPS Paediatric Emergency Medicine Section; Marie-Joëlle Doré-Bergeron MD, CPS Hospital Paediatrics Section

Principal authors: Laurel Chauvin-Kimoff MD, Allan DeCaen MD

References

Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.