5.2 Severe Viral Bronchiolitis, RSV & High-Flow Nasal Cannula (HFNC) Therapy

Severe bronchiolitis and high-flow nasal cannula

Recognize the syndrome and reassess the trajectory

Bronchiolitis usually affects infants and children younger than 2 years. Coryza and cough often precede tachypnea, retractions, diffuse wheezing or crackles, and reduced feeding. RSV is a common cause. Other respiratory viruses can produce the same syndrome. Inflammation, airway wall edema and mucus or epithelial debris narrow small airways. Partial obstruction favors air trapping, and obstructed units may become atelectatic. Uneven ventilation relative to perfusion impairs oxygenation. Rising carbon dioxide with fatigue or decreasing respiratory effort signals inadequate ventilation.

Young corrected age, low birth weight and prior apnea during this illness raise concern for inpatient apnea. Prematurity, chronic lung disease, significant congenital heart disease, impaired secretion clearance and immunocompromise increase concern for severe disease. Apnea can precede obvious lower-airway findings. A viral result cannot establish the mechanism of an individual apneic event or exclude pertussis, bacterial infection or another cause. Consider an alternative diagnosis when the age, focal findings or course are atypical. In a febrile young infant, apply the appropriate age-based evaluation. WHO 2026 bronchiolitis guideline · Prospective apnea cohort · Prospective severe disease cohort

Compare work of breathing, air entry, alertness, perfusion, saturation trend, feeding and urine output. Head bobbing, grunting and marked retractions suggest severe distress. Less effort accompanied by shallow breathing, poorer air entry or lethargy can mean fatigue. If the infant is apneic and inadequately breathing with a pulse, call for help and start effective bag-mask ventilation with oxygen. Reassess heart rate and perfusion, and follow PALS if bradycardia and compromise persist despite effective ventilation. Once stabilized, monitor an infant with significant apnea continuously and arrange critical care evaluation. 2025 AHA/AAP pediatric basic life support · 2025 pediatric advanced life support

Oxygen, airway clearance and hydration

• Oxygen: For an otherwise healthy infant aged at least 6 weeks with moderate disease and persistent SpO₂ below 90%, confirm signal quality and start low-flow oxygen with prompt reassessment. A trial in hospitalized infants older than 6 weeks through 12 months corrected age found a 90% target equivalent to 94% for cough resolution. Use closer monitoring and individualized goals for younger or high-risk infants. For example, the 2025 Australasian guideline uses a threshold below 92% for infants under 6 weeks or under 12 months with an underlying condition. Apply cardiac targets to the child's lesion and baseline.
• Nasal clearance: Use gentle superficial suction when secretions impair breathing or feeding. Reassess after suction and avoid routine deep suctioning.
• Feeding: Observe breathing, alertness and coordination during oral intake. Escalating support, marked distress, recurrent apnea or weak airway protection favors pausing oral intake. Use nasogastric hydration when the child is stable enough for enteral therapy, or IV hydration when enteral delivery is unsafe or poorly tolerated. A randomized trial in infants aged 2–12 months found no significant difference in length of stay between routes. Selected stable children can feed while receiving HFNC. For eligible children at least 28 days old who need maintenance IV fluids, use isotonic fluid with appropriate glucose and potassium based on renal function, urine output and laboratory results. Reassess fluid balance and electrolytes.
• Testing and medication: Typical disease is a clinical diagnosis. Avoid routine chest radiographs and blood tests. Consider targeted testing for an unexpected course, a complication, or impending respiratory failure, without delaying stabilization. Avoid routine albuterol, epinephrine, systemic steroids, chest physiotherapy or antibiotics in typical disease. Treat a suspected serious bacterial infection promptly when warranted. The 2025 Australasian guideline conditionally permits combined corticosteroids and inhaled epinephrine for severe disease requiring ICU care. This is a setting-specific option and does not justify routine use for moderate disease.

AAP acute bronchiolitis guideline · BIDS oxygen trial · 2025 Australasian guideline · Hydration trial · Pediatric HFNC feeding cohort · AAP maintenance IV fluid guideline

HFNC selection and failure

When low-flow oxygen and initial care fail to meet oxygenation or work-of-breathing goals, consider heated, humidified high flow in an appropriately monitored setting. Severe distress warrants early critical care evaluation and a choice of support based on the child's condition. In a 1,472-infant trial outside the ICU, protocol-defined escalation occurred in 12% on early HFNC versus 23% on standard oxygen. The trial did not show an intubation or length-of-stay benefit. In the PICU TRAMONTANE trial of young infants with moderate to severe bronchiolitis, initial HFNC did not meet the noninferiority criterion versus nasal CPAP for treatment failure. In the ward trial, 102 of the 167 infants whose standard oxygen treatment failed responded to rescue HFNC. The 2026 WHO guideline conditionally favors high flow for hospitalized hypoxemic children under 2, with standard low flow as the initial step in most cases. The 2025 Australasian guideline also favors low flow first for moderate hypoxemic bronchiolitis.

High flow washes exhaled gas from the upper airway and may reduce room air entrainment when flow approaches inspiratory demand. The device heats and humidifies the gas. Distending pressure varies with the interface, leak, mouth position and flow. Choose prongs that leave a leak around them per the device instructions. There is no reliable conversion from L/kg/min to airway pressure. Use regulated CPAP when the clinical plan calls for a set distending pressure.

Worked flow example. A 2026 U.S. Delphi panel supported starting at 1.5–2 L/kg/min when HFNC is indicated. At a protocol setting of 2 L/kg/min, an 8 kg infant receives 16 L/min, provided the device, cannula and unit permit that flow. Set inspired oxygen separately and titrate to the clinical target. Reassess breathing effort, air entry, alertness, oxygen requirement, apnea and perfusion early and after each adjustment. A higher saturation with worsening fatigue or rising CO₂ is a poor response. ROX research in infant bronchiolitis has produced inconsistent results. Bedside escalation should proceed when indicated regardless of score or elapsed time. As work of breathing and oxygen needs improve, reduce support by the unit pathway and reassess after each change. Consider CPAP or bilevel support for selected spontaneously breathing infants with close supervision. Recurrent apnea requiring rescue, inability to protect the airway, worsening ventilation despite support or shock may require invasive ventilation without an intervening noninvasive trial. Ward trial · PICU trial · U.S. HFNC Delphi consensus · CHOP inpatient pathway · HFNC physiologic study · Cannula manufacturer · Pediatric ROX studies and ward validation

Prevent severe RSV in the United States

For the 2026–2027 season, AAP recommends one infant antibody for eligible infants younger than 8 months born during or entering their first season when maternal vaccination is absent, unknown or given fewer than 14 days before birth. Consider exceptions after adequately timed maternal vaccine for particular high-risk infants, such as after cardiopulmonary bypass, or if maternal immune response or antibody transfer may be inadequate. First-season dosing is one IM injection of nirsevimab 50 mg if under 5 kg or 100 mg if at least 5 kg, or clesrovimab 105 mg regardless of weight. Give eligible infants born during the season a dose in the first week if possible, ideally during the birth hospitalization. Local epidemiology can change seasonal timing.

In the second season the AAP recommends nirsevimab 200 mg IM as two 100 mg injections for eligible high-risk children aged 8 through 19 months. The 2026 AAP list expands beyond the older CDC categories and includes birth before 32 weeks, hemodynamically significant congenital heart disease, and certain pulmonary, neuromuscular and chromosomal conditions. Other eligible groups include children with severe immunocompromise, cystic fibrosis with severe lung disease or weight-for-length below the 10th percentile, and American Indian or Alaska Native children. For the chronic lung disease criterion, the AAP requires medical support in the 6 months before the season. Use chronological age for immunization eligibility. The FDA nirsevimab indication extends through age 24 months for children who remain vulnerable in their second season. AAP seasonal eligibility uses the narrower age range above. The current clesrovimab indication is first-season prevention. Palivizumab is no longer available in the United States.

Maternal Pfizer RSVpreF vaccine is given at 32 weeks 0 days through 36 weeks 6 days when eligible. The CDC and ACOG advisory window for most of the continental U.S. is September through January. SMFM expanded its own guidance in September 2026 to September 1 through March 1. Use the applicable obstetric guidance and local circulation. The antibodies and maternal vaccine are prevention strategies. AAP 2026–2027 policy · CDC infant guidance · Current nirsevimab label · Current clesrovimab label · ACOG maternal guidance · SMFM 2026 update