INTRODUCTION — This topic will focus on the use of high-flow nasal cannula (HFNC) in pediatric patients, including discussion of equipment, proposed mechanisms of action, comparison with other oxygen delivery devices, indications and contraindications, approach to initiation, assessment of effectiveness, and potential complications.
The use of HFNC for bronchiolitis and for premature and term neonates is discussed separately:
DESCRIPTION — HFNC oxygen therapy, also referred to as heated, humidified, high-flow nasal cannula (HHHFNC), involves the delivery of an adjustable mixture of heated and humidified air and oxygen at rates that exceed spontaneous inspiratory flow. There is no single definition of what constitutes high flow, as rates will vary by the age and weight of the patient, with a range of 2 to 60 L/min. The use of HFNC has been increasing over time as equipment has become more widely available and indications for use have grown [1-4]. In addition, HFNC is easy to apply and well tolerated by most patients, furthering the appeal. While originally restricted to intensive care units, its use has now expanded to emergency departments, inpatient pediatric wards, and pre- and interhospital transport settings [5-11].
EQUIPMENT — HFNC systems include a number of parts (figure 1):
●Generator to create flow
●Blender to mix air and oxygen
●Chamber to condition (ie, heat and humidify) the air
●Circuit to reach the patient
●Patient interface (eg, nasal cannula or prongs)
●Pressure-relief valve (optional safety mechanism to stop flow when a predetermined pressure is reached)
Nebulized therapy such as bronchodilators [12-15] as well as helium-oxygen mixtures and inhaled nitric oxide [16-18] can be delivered using HFNC, although data regarding efficacy and safety are limited to in vitro studies and small pediatric case series. Furthermore, the rate of delivery of medication is difficult to estimate and is likely to be reduced at higher flow rates ; improved clinical outcomes have not been demonstrated compared with jet nebulization. For these reasons, we do not routinely deliver medication using HFNC.
MECHANISMS OF ACTION — There are a number of proposed mechanisms by which HFNC might be beneficial for infants and children with respiratory illness, including:
●Washout of nasopharyngeal dead space – High-flow delivery washes out the end-expiratory gas within the oro- and nasopharynx. The upper airway then serves as an anatomic reservoir with richly oxygenated air from which the patient draws each breath, minimizing the entrainment of room air [19-22].
●Reduction in upper airway resistance – By providing gas flows that match or exceed spontaneous inspiratory flow rates, HFNC minimizes inspiratory resistance across the nasopharynx. The resultant reduction in work of breathing has been demonstrated in studies in neonates and infants by measuring diaphragmatic electrical activity and respiratory plethysmography [21,23-25].
●Optimal conditioning of gas – Delivering gases that have been previously heated and humidified reduces the energy expenditure required by the body for conditioning. This is particularly valuable for children with respiratory illness who may be tachypneic and rapidly turning over their tidal volume because optimal conditioning contributes to reductions in oxygen demand . It also avoids an increased risk of bronchospasm and airway resistance compared with the delivery of cold, dry air .
●Positive distending pressure – High flow rates provide positive distending pressure in the pharynx, which can prevent collapse and improve work of breathing. The amount of pressure varies based on flow rate, fit of the nasal prongs, and mouth opening . In a study of infants with bronchiolitis, a flow rate of 2 L/kg per minute resulted in mean pharyngeal pressures >4 cm H2O and improved breathing . In adults, a linear relationship is noted between flow rates and pharyngeal pressure, ranging from 1 to 4 cm H2O when the mouth is closed (figure 2). (See "Heated and humidified high-flow nasal oxygen in adults: Practical considerations and potential applications".)
●Impact of mouth opening – Studies in children have documented a difference in increased pharyngeal pressure during HFNC when the mouth is closed compared with when it is open [27,29]. Therefore, in infants, concurrent use of a pacifier may be helpful in achieving the full benefit of HFNC.
COMPARISON WITH OTHER MODES OF OXYGEN DELIVERY — HFNC offers distinct advantages over other modes of oxygen delivery and respiratory support without compromising ease of initiation or patient comfort. Many of the clinical trials comparing these approaches have been performed in patients with bronchiolitis. (See "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Noninvasive ventilation'.)
●Low-flow nasal cannula – Flow rates through nasal cannula have traditionally been limited to low flow (<2 L/min in infants and <6 L/min in children) to avoid desiccation of the nasal mucosa and discomfort to the patient. Humidifying and heating the gas mixtures reduces these concerns and permits delivery of higher flow rates and improved oxygen delivery. In addition, the HFNC blender allows for adjustment of the concentration of inspired oxygen rather than just adjustment in flow. For example, an observational study in 40 children with moderate to severe bronchiolitis (in contrast to bronchiolitis generally) showed more rapid improvements in respiratory rate, work of breathing, and ability to feed in infants treated with HFNC compared with low-flow nasal cannula .
●Face mask – Face masks are often perceived as constricting, limit the ability to speak or drink, and are not well tolerated by many pediatric patients. In addition, HFNC has been shown to provide better oxygen delivery than face masks. The majority of comparative trials have been performed following extubation [31,32]; however, one study of adult patients with hypoxemic respiratory failure found higher partial pressure of oxygen (PaO2) concentrations when managed with HFNC compared with oxygen delivery using a face mask .
●Masks with diffuser – OxyMask is a specialized face mask that directs oxygen toward the nose and mouth using a diffuser system (see "Continuous oxygen delivery systems for the acute care of infants, children, and adults", section on 'Face masks'). The open design has the potential to be less frightening to pediatric patients yet deliver high concentrations of oxygen. However, HFNC, in addition to being well-tolerated by pediatric patients, provides positive pressure, which may make it a better choice for oxygen delivery in patients with specific conditions, such as bronchiolitis. As an example, in a randomized controlled trial of 60 infants with moderate to severe bronchiolitis receiving treatment in an intensive care unit, individuals receiving HFNC rather than the OxyMask had fewer treatment failures (0 versus 7, respectively) and were weaned from oxygen sooner (56 versus 96 hours) . This result likely reflects the benefits of positive pharyngeal pressure and conditioning that are provided by HFNC. (See 'Mechanisms of action' above.)
●Noninvasive ventilation (CPAP) – Continuous positive airway pressure (CPAP) offers airway-distending pressure that can help with work of breathing and oxygenation for children with respiratory disease. Most comparative studies between CPAP and HFNC have been performed in patients with bronchiolitis. (See "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Noninvasive ventilation'.)
Other studies have compared these therapies for other diagnoses as well. For example, HFNC appears to be at least as good as CPAP for pediatric patients requiring noninvasive respiratory support and may be better tolerated by the patient. In an unblinded, multicenter trial of over 570 infants (median age 9 to 10 months) assessed to require noninvasive respiratory support and randomly assigned to HFNC or CPAP for their underlying condition (approximately 50 percent with bronchiolitis; 20 to 25 percent with asthma, upper airway problem, or other respiratory condition; and the rest with nonrespiratory conditions including sepsis), the duration of noninvasive respiratory support and the proportion requiring endotracheal intubation were similar in both groups . Patients assigned to HFNC had significantly lower use of sedation (28 versus 37 percent), shorter mean duration of intensive care unit stay (5 versus 7.4 days), and shorter mean duration of hospitalization (13.8 versus 19.4 days). Patients assigned to CPAP had more nasal trauma. These findings contrast with results from smaller trials in patients with respiratory conditions other than bronchiolitis that have suggested shorter time to improvement and reduced need for change in respiratory management for CPAP compared with HFNC [36,37]. However, in addition to the higher risk of nasal trauma for patients receiving CPAP described above, CPAP is also louder than HFNC, not always tolerated by young infants, and may increase the risk of skin breakdown .
INDICATIONS — HFNC may be trialed in any patient with severe respiratory distress or hypoxemia who can maintain their airway (alert and able to swallow), and who does not have other contraindications. (See 'Contraindications' below.)
HFNC offers many of the benefits of noninvasive positive-pressure ventilation and is often easy to initiate and frequently well tolerated by children. It may prevent progression to noninvasive or mechanical ventilation in selected patients. The majority of clinical experience for HFNC outside of neonates comes from management of patients with bronchiolitis. The use of HFNC for the treatment of bronchiolitis is discussed in detail separately. (See "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Noninvasive ventilation'.)
Other respiratory conditions where HFNC may have a potential benefit include:
●Respiratory distress/dyspnea – HFNC has the ability to offload the work of breathing; therefore, it may be used in patients with dyspnea who are not responsive to alternative means of oxygen delivery or disease-specific therapies (eg, bronchodilators for status asthmaticus or racemic epinephrine for croup). Trials suggest that HFNC can reduce respiratory distress and improve oxygen saturation in infants and children with respiratory distress from a variety of causes [8,35,36,38]. However, a significant proportion of these patients are at risk for treatment failure, necessitating endotracheal intubation and mechanical ventilation (up to 15 percent of critically ill patients in one trial) . Thus, close monitoring and frequent reassessment is an essential component of proper delivery of HFNC. (See 'Assessment of effectiveness' below.)
●Asthma – Although evidence is limited, HFNC has been safely used for children with status asthmaticus as described separately. (See "Acute severe asthma exacerbations in children younger than 12 years: Intensive care unit management", section on 'High-flow nasal cannula'.)
●Tracheomalacia – HFNC has the potential to generate airway-distending pressure, which has been described in case reports for patients with tracheomalacia. (See "Congenital anomalies of the intrathoracic airways and tracheoesophageal fistula".)
●Preoxygenation/apneic oxygenation during intubation – Data for apneic oxygenation in children are currently limited; however, integration into practice is increasing. HFNC has potential advantages as a system for oxygenation delivery prior to and during endotracheal intubation as follows:
•Increased oxygen delivery compared with other modes of oxygenation during intubation (see 'Comparison with other modes of oxygen delivery' above)
•Reduced bronchospasm (humidified, heated gas delivery)
•No change of oxygen-delivery equipment needed when preparing to escalate care to endotracheal intubation and mechanical ventilation
The benefit of HFNC as a tool for preoxygenation or apneic oxygenation needs to be weighed against potential downsides, including the delay in setup if not already in place, the possibility of gastric distension, and the inability to create an effective mask seal over the larger nasal cannula were mask ventilation to be required during the procedure.
In a small trial of 48 children requiring intubation for elective surgery or advanced imaging, the addition of HFNC oxygen delivery (range of flow rates from 2 to 50 L/min) as part of the induction protocol increased oxygenated apnea time compared with routine induction with standardized bag-mask ventilation (192 versus 109 seconds, respectively) .
●Hypoxemic respiratory failure – HFNC oxygen therapy appears to provide support similar to CPAP for children with hypoxemic respiratory failure. For example, in a multicenter trial of HFNC versus CPAP in critically ill children, HFNC was similar to CPAP for time to liberation from respiratory support and need for endotracheal intubation; over 40 percent of patients had an oxygen requirement consistent with pediatric acute respiratory distress syndrome .
However, HFNC oxygen therapy may not have better efficacy than standard oxygen therapy for children with mild to moderate acute hypoxemic respiratory failure (AHRF). For example, in the multicenter PARIS-2 trial of over 1500 children (median age 1.9 years) hospitalized with mild to moderate acute hypoxemic respiratory failure defined as increased work of breathing, respiratory rate ≥35 per minute, and oxygen requirement to maintain pulse oximetry over 90 to 92 percent, patients assigned to HFNC oxygen therapy, compared with standard oxygen therapy, had longer length of stay (1.77 versus 1.5 days) and more ICU admissions (12.5 versus 6.9 percent, adjusted odds ratio [aOR] 1.9, 95% CI 1.4-2.8) [40,41]. Adverse events were low in both groups. These findings do not support the routine use of HFNC oxygen therapy in young children with mild to moderate acute hypoxemic respiratory failure.
CONTRAINDICATIONS — HFNC should not delay advanced airway management in a patient deemed to require immediate endotracheal intubation. This may include patients with acutely impaired mental status, risk of aspiration, or other need for airway protection.
HFNC should also be avoided in the following conditions:
●Hypercapnic respiratory failure
●Facial anomalies (eg, choanal atresia) or injuries that preclude appropriate nasal cannula fit
●Excessive oral or nasal secretions
●Existing air leak (eg, pneumothorax or pneumomediastinum)
●Agitation or confusion predicting inability to tolerate
PATIENT SELECTION — Appropriate patient selection is essential to the successful use of HFNC. Before initiating its use, all of the following should be determined:
●No contraindications to HFNC (see 'Contraindications' above)
●High likelihood that the patient will tolerate HFNC (commonly well tolerated in children)
●Reasonable expectation that HFNC will be adequate to stabilize and/or reverse the current respiratory status (see 'Indications' above)
INITIATION — HFNC is relatively simple to initiate. After an appropriately sized nasal cannula and circuit is selected for the patient, the clinician can determine delivery settings, including air temperature, flow rate, and fraction of inspired oxygen (FiO2). Humidification varies with chosen air temperature. Initial flow rates and FiO2 will vary by age/size of patient and indication/severity of disease, and they can be increased pending response to initial settings.
COVID-19 precautions — HFNC oxygen therapy is considered an aerosol-generating procedure. Thus, appropriate infection control precautions are required when it is being administered to patients with unknown or positive coronavirus disease 2019 (COVID-19) status as discussed separately. (See "COVID-19: Infection prevention for persons with SARS-CoV-2 infection", section on 'Aerosol-generating procedures/treatments' and "COVID-19: Respiratory care of the nonintubated hypoxemic adult (supplemental oxygen, noninvasive ventilation, and intubation)", section on 'Infection control precautions for noninvasive modalities'.)
Cannula selection — Cannulae used to deliver high flow do not require a seal to function and therefore have prongs with smaller diameter and length than interfaces designed for continuous positive airway pressure (CPAP).
●Recommendations are for the cannula to occupy approximately 50 percent of the internal diameter of the nares to permit some leak and prevent excessive airway pressure [42,43].
●The distance between the prongs should be wide enough to avoid pinching the nasal septum.
Initial settings — HFNC settings can be started based on perceived need and adjusted based on clinical response as measured by work of breathing and continuously monitored heart rate, respiratory rate, and oxygen saturation [44-46].
●Temperature is commonly set at 37°C to maximize humidification, although this may be adjusted based on clinical context.
●Initial flow rates should be based on patient age or size and advanced as needed. The table offers suggested initial and maximal flow rates (table 1). Alternatively, flow rates can be started at 1 to 2 L/kg per minute up to the maximum flow rate for age. A study of children younger than three years of age showed that work of breathing was improved with increasing flow rates with maximal improvement at 2 L/kg per minute but similar improvement at 1.5 L/kg per minute.
●FiO2 can be set between 0.21 and 1 based on clinical circumstance. General practice is a goal oxygen saturation between 94 and 99 percent rather than 100 percent (to avoid oxygen toxicity).
Assessment of effectiveness — A number of metrics can be used to assess the patient response to HFNC therapy.
●Vital signs – Infants started on HFNC therapy often show improvement in heart rate and respiratory rate (specifically reduced tachycardia and tachypnea) as early signs of responsiveness [6,7,28,30]. Responsiveness may be seen within the first hour of therapy, though in some individuals, it may take several hours before improvement is evident.
●Work of breathing – HFNC can significantly offload work of breathing. Electrical activity of the diaphragm and decreased swings in esophageal pressure can document such physiologic changes but are not useful clinically . Pediatric scoring systems to guide clinical assessment are available, such as disease-specific respiratory scores for bronchiolitis and asthma (table 2) as well as general respiratory distress scores. (See "Bronchiolitis in infants and children: Clinical features and diagnosis", section on 'Severity assessment'.)
●Oxygen requirement – Oxygenation should improve following the initiation of HFNC. In one study, an oxygen saturation (SpO2)/FiO2 ratio of >200 at 60 minutes was associated with successful therapy with HFNC .
COMPLICATIONS — Evidence is limited regarding the safety of HFNC therapy for respiratory support in children . However, despite increasing use in multiple settings, reported serious complications from HFNC therapy are limited to case reports of air leak and pneumocephalus [49,50], and rates of adverse events are lower than with continuous positive airway pressure (CPAP) and comparable to standard oxygen therapy (<1 percent) .
The risk of complications secondary to high airway pressure and traumatic air dissection can be further reduced with pressure-relief valves built into some HFNC systems. In addition, using the lowest effective flow rates and ensuring appropriate selection of nasal cannula size to allow sufficient leak can be protective .
SUMMARY AND RECOMMENDATIONS
●Terminology – High-flow nasal cannula (HFNC) oxygen therapy (figure 1), also referred to as heated, humidified, high-flow nasal cannula (HHHFNC), involves the delivery of an adjustable mixture of heated and humidified air and oxygen at rates that exceed spontaneous inspiratory flow. There is no single definition of what constitutes high flow because rates will vary by the age and weight of the patient, with a range of 2 to 60 L/min. (See 'Description' above and 'Equipment' above.)
●Benefits – HFNC oxygen therapy offers distinct advantages over other modes of oxygen delivery and respiratory support without compromising ease of initiation or patient comfort, including better oxygen delivery than low-flow nasal cannula, face mask, or mask with diffuser systems and better comfort than noninvasive ventilation. (See 'Comparison with other modes of oxygen delivery' above.)
●Indications – HFNC oxygen therapy may be trialed in any patient who can maintain their airway (alert and able to swallow), who does not have contraindications to its use as described below, and who has severe respiratory distress or hypoxemia. (See 'Indications' above.)
●Contraindications – HFNC oxygen therapy should not delay advanced airway management in a patient deemed to require immediate endotracheal intubation. This may include patients with acutely impaired mental status, risk of aspiration, or other need for airway protection. (See 'Contraindications' above.)
HFNC oxygen therapy should also be avoided in the following conditions (see 'Contraindications' above):
•Hypercapnic respiratory failure
•Facial anomalies (eg, choanal atresia) or injuries that preclude appropriate nasal cannula fit
•Excessive oral or nasal secretions
•Existing air leak (eg, pneumothorax or pneumomediastinum)
•Agitation or confusion predicting inability to tolerate
●Procedure – Initiation of HFNC oxygen therapy is described in detail in the topic. After an appropriately sized nasal cannula and circuit is selected for the patient, the clinician can determine delivery settings, including air temperature (typically 37°C), flow rate, and fraction of inspired oxygen (FiO2). Humidification varies with chosen air temperature. (See 'Initiation' above.)
Initial flow rates and FiO2 will vary by age/size of the patient (table 1) and indication/severity of disease, and they can be adjusted pending response to initial settings.
Response to therapy can be measured by evaluating for improvement in vital signs (eg, decreased tachycardia and/or tachypnea), decreased work of breathing, and improved oxygenation. (See 'Assessment of effectiveness' above.)
●Complications – Serious complications, such as pneumothorax, can occur with HFNC oxygen delivery, but the rates of adverse events are comparable with standard oxygen therapy (<1 percent) and are less than what is reported in patients receiving continuous positive airway pressure (CPAP) or mechanical ventilation. (See 'Complications' above.)
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