The goal of this observational study is to identify the variables that predict treatment failure in order to identify the patients in which HFNC treatment may fail and not delay the transition to advanced respiratory support treatments in these patients.

The main questions it aims to answer are:

• What factors contribute to the failure of HFNC treatment in these children?
• What is the frequency of HFNC treatment failure in children with moderate and severe respiratory distress? Researchers will compare the group whose HFNC treatment was successful with the group whose HFNC treatment failed to identify factors that cause treatment failure.

Oxygen therapy with a high-flow nasal cannula (HFNC) is a well-tolerated, relatively new, non-invasive alternative ventilation treatment modality. On the other hand, HFNC failure delays advanced respirator supportive treatments, prolongs hospitalization in the intensive care unit, and emergency department, and causes a significant increase in morbidity and mortality with hypoxemia, neurological impairment, and/or hemodynamic instability. The investigators aimed to identify the variables that predict treatment failure in order to identify the patients in which HFNC treatment may fail and not delay the transition to advanced respiratory support treatments in these patients.

Inclusion Criteria:

• Moderate to severe respiratory distress
• Oxygen therapy with high-flow nasal cannula

Exclusion Criteria:

• Chronic lung disease (those with CO2 retention or hypoxia in their daily life)
• Cyanotic congenital heart disease
• Craniofacial malformation
• Trauma patients
• Hypotonic patients
• Cases with tracheostomy
• Patients using HFNC therapy for respiratory support after extubation

1 months-18 years Moderate to severe respiratory distress Oxygen therapy with high-flow nasal cannula