Acute Bronchiolitis in Infants on Invasive Mechanical Ventilation: Physiology Study of Airway Closure

OBJECTIVES: This study aimed to explore whether airway closure can be detected in patients with severe acute bronchiolitis on invasive mechanical ventilation. DESIGN: Single-center prospective physiologic study carried out in 2023–2024. SETTING: PICU in a tertiary-care general hospital. PATIENTS: Infants with acute bronchiolitis undergoing invasive mechanical ventilation. INTERVENTIONS: Under deep sedation and neuromuscular blockade, the mechanical ventilator, in a volume-controlled mode, was transiently set with a respiratory rate of five breaths/min, a tidal volume of 6 mL/kg of ideal body weight, positive end-expiratory pressure 0 cm H 2 O, a flow rate of 2 L/min, an inspiratory-expiratory ratio of 1:1, and a F io 2 of 1.0. After recording three breath cycles, the patient was returned to baseline ventilatory settings. MEASUREMENTS AND MAIN RESULTS: We identified the presence of airway closure through the low-flow pressure-volume curve obtained from a pneumotachometer with a flow sensor placed at the Y-piece and simultaneously from the pressure-impedance curve and ventilation maps acquired using electrical impedance tomography. We included 12 patients, and airway closure was detected in seven of them. The median (interquartile range [IQR]) airway opening pressure was 14 cm H 2 O (IQR, 11–17 cm H 2 O). Patients with airway closure exhibited high levels of driving pressure, with a median of 16 cm H 2 O (IQR, 11–17 cm H 2 O), and low levels of respiratory system compliance, with a median of 0.41 mL/cm H 2 O/kg (IQR, 0.38–0.59 mL/cm H 2 O/kg). When these parameters were corrected for airway opening pressure, there was a significant decrease in driving pressure to 9 cm H 2 O (IQR, 8–12 cm H 2 O; p = 0.018) and a significant increase in respiratory system compliance to 0.70 mL/cm H 2 O/kg (IQR, 0.53–0.81 mL/cm H 2 O/kg; p = 0.018). CONCLUSIONS: Airway closure requiring high opening pressures can be detected in ventilated infants with acute bronchiolitis, and this phenomenon may impact respiratory mechanics.