The purpose of the present project is to compare High-Flow Nasal Oxygen therapy with Standard Oxygen therapy, initiated in the prehospital setting in patients with acute hypoxemia respiratory failure, in terms of oxygenation at arrival to the hospital and need of mechanical ventilation during the subsequent 28 days

Patients with respiratory distress and an SpO2 below 90% in the prehospital setting will be randomized to receive either high-flow nasal oxygen therapy through a dedicated device or standard oxygen therapy through standard devices such as nasal cannula or face mask. Need of mechanical ventilation either invasive or noninvasive from enrollment to day 28 and time course of oxygenation between first SpO2 measured on scene and arrival to the hospital will be the main outcome measures.

Inclusion Criteria:

• Age ≥ 18 years
• First SpO2 on scene <90%
• At least one other sign of respiratory distress defined by (a) respiratory distress with a respiratory rate ≥ 25/min; (b) laboured breathing
• No advance directives or known decisions of Do Not intubate or Do Not Ventilate order.

Exclusion Criteria:

• Known COPD or other hypercapnic chronic respiratory failure
• age <18 years
• Pregnancy or breastfeeding
• Anatomical factors precluding the use of a nasal cannula
• Emergency intubation required
• Patients with tracheostomy
• Patient transported to a hospital not involved in the study