This study aims to examine the tolerance, feasibility, and physiological effects in airway clearance by using a novel non-invasive oscillating transducer device (NIOD, FrequencerTM) in critically ill children. The project is two years long with two separate stages of investigation. This study specifically examines different frequencies of NIOD to find the best frequency on patients outcomes.

Airway obstruction due to excessive production of secretion in small children especially those with bronchiolitis is a critical problem in the clinical management. Chest physiotherapy (CPT) and an invasive positive percussion ventilation (IPPV) have been recognized as to encourage dislodging the secretions; nonetheless, the tolerance to the procedure and its efficiency have not been proved to be sufficient. This study aims to examine the tolerance, feasibility, and physiological effects in airway clearance by using a novel non-invasive oscillating transducer device (NIOD) in critically ill children. The study will be prospective Crossover Randomized Study in a Pediatric Intensive Care Unit in a Canadian Academic Children's Hospital. We will target children less than 24-month-old, for whom CPT is prescribed for airway clearance with or without atelectasis. We will apply two different frequencies of NIOD (i.e. 40 and 60Hz) for 3 minutes each, on each patient 3 hours apart. The investigators will apply a pragmatic design, so that other procedures including hypertonic saline nebulization, IPPV, suctioning (e.g., oral or nasal), or changing the ventilator settings or modality (i.e., increasing PEEP or changing the nasal mask to total face CPAP) can be provided at the direction of bedside pediatric intensivists in charge.

Inclusion Criteria:

• All the patients admitted to the PICU during the study period will be screened. The investigators will not set any restriction regarding the timing of prescription of CPT (i.e., length of PICU stay before screening) for the screening. The investigators will include only if CPT is expected to be used as a management at least for the next 24 hours in the PICU from the time of inclusion. For instance, if CPT will be expected to be discontinued from the management in a day, the investigators will exclude the participants from the inclusion. CPT can be prescribed for airway clearance with any etiology such as atelectasis at the directions of bedside pediatric intensivists in charge on the study date. The investigators will only include patients whose oxygenation is stable (SpO2>90%) with less than 0.60 of ventilators.

Exclusion Criteria:

• CPT order will (or is expected to) be discontinued within 24 hours from the inclusion timing.
• CPT is not ordered for airway clearance.
• SpO2 is not stable (SpO2=<90%) with more than 0.60 of FIO2 for the ventilated patients including patients on NIV, at least for previous 1 hour from the screening.
• SpO2 is not stable (SpO2=<90%) with more than 0.60 of FIO2 for the patients on HFNC, at least for previous 1 hour from the screening.
• Bradycardia (HR<80bpm) at any interventions at least for 24 hours prior to the screening.
• Patients with known pneumothorax, osteomyelitis in the PICU admission.
• Known pulmonary hypertension with treatment(s) underway.
• Thoracotomy within 1 month.
• Known recent/unhealed rib fractures.
• Known skin injury of chest wall.
• No obtain of IC.
• Brain death or vegetated states.