Clinical Progress Note: High Flow Nasal Cannula Therapy for Bronchiolitis Outside the ICU in Infants

Viral bronchiolitis is the most common indication for infant hospitalization in the United States.¹ The treatment mainstay remains supportive care, including supplemental oxygen when indicated.¹ High flow nasal cannula (HFNC) therapy delivers humidified, heated air blended with oxygen, allowing much higher flow rates than standard nasal cannula therapy and is being used more frequently in inpatient settings.

Infants and toddlers with bronchiolitis develop increased work of breathing to preserve oxygenation and ventilation in the setting of altered airway resistance and lung compliance.^2,3 In addition to oxygen supplementation, HFNC is used to reduce work of breathing through several mechanisms:^2-6 (1) Nasopharyngeal dead space washout clears oxygen-depleted gas at the end of expiration, facilitating alveolar ventilation (ie, carbon dioxide retention improves); (2) High flow rates match increased inspiratory flow demands of acutely ill patients, reducing nasopharyngeal inspiratory resistance and optimizing dead space washout, thus decreasing work of breathing; (3) Adequate flow rates generate distending pressure, which prevents pharyngeal collapse, supports lung recruitment, and reduces respiratory effort (demonstrated in younger infants); and (4) HFNC systems heat and humidify the breathing gas, reducing the metabolic work required to condition cool, dry gas and improving conductance and pulmonary compliance.^2-5

HFNC therapy is used more commonly in acute care units despite limited literature on its effectiveness outside the intensive care unit (ICU).^7,8 We asked the question, “Does use of HFNC therapy for infants with bronchiolitis hospitalized in acute care units result in improved outcomes when compared with standard nasal cannula oxygen therapy, including length of stay (LOS), oxygen therapy duration, and preventing escalations of care such as ICU transfer, positive pressure ventilation, and intubation?” Also, do published studies provide guidance for the initiation and management of HFNC? We focused our search on studies published in the last five years that included patients with bronchiolitis treated with HFNC outside the ICU; here, we review those studies most relevant to pediatric hospitalists.

No guideline exists for initiating flow or fraction of inspired oxygen (FiO₂). HFNC may be initiated for hypoxia, increased work of breathing, or both in patients with bronchiolitis. To achieve optimal dead space washout, inspiratory flow, and distending pressure, initial flow rates should be 1.5 to 2 L/kg/min, particularly for infants and young children.^2-5 Weiler et al.³ evaluated the breathing effort of ICU patients at 0.5, 1, 1.5, and 2 L/kg/min and found optimal flow rates for improved work of breathing were 1.5-2 L/kg/min. The smallest patients, ≤8 kg, saw the greatest benefit, a finding likely explained by larger anatomic dead space in infants/small children compared with older children.³ For older/larger children (>20 kg), an initial flow closer to 1 L/kg/min is often appropriate.⁵ When used for hypoxia, initiating flow without supplemental FiO₂ may improve oxygenation by flushing nasopharyngeal dead space. FiO₂ should be titrated to achieve the goal set by the treatment team, often ≥90%. Improvement in heart rate and peripheral oxygen saturation (SpO₂) can be observed within 60 minutes of initiating HFNC in patients responsive to therapy.⁶