Inclusion Criteria:  Pediatric patients older than 1 month and younger than18 years of age; hospitalized at the PICU with the intention of treatment with HFOT at least for the upcoming 5 hours Requiring FiO2 ≥ 25% to keep SpO2 in the target ranges defined by the clinician Written informed consent signed and dated by the patient or one relative in case that the patient is unable to consent, after full explanation of the study by the investigator and prior to study participation  Exclusion Criteria:  Patient with indication for immediate noninvasive ventilation (NIMV), or invasive mechanical ventilation (IMV) Hemodynamic instability defined as a need of continuous infusion of epinephrine or norepinephrine > 1 mg/h Low quality on the SpO2 measurement using finger and ear sensor (quality index below 60% on the SpO2 sensor, which is displayed by a red or orange colour bar) Severe acidosis (pH ≤ 7.25) Pregnant woman Patients deemed at high risk for the need of mechanical ventilation within the next 5 hours Patients deemed at high risk for the need of transportation from PICU to another ward, diagnostic unit or any other hospital Diseases or conditions which may affect transcutaneous SpO2 measurement such as chronic or acute dyshemoglobinemia: methemoglobinemia, carbon monoxide (CO) poisoning, sickle cell disease Formalized ethical decision to withhold or withdraw life support Patient included in another interventional research study under consent Patient already enrolled in the present study in a previous episode of acute respiratory failure