The goal of this clinical trial is to test if treatment with prehospital Non-invasive ventilation (NIV) for patients with acute respiratory failure (ARF), due to acute exacerbation of chronic obstructive pulmonary disease (AECOPD) based on in-hospital criteria, should be used in the prehospital setting. This is performed with the introduction of prehospital arterial blood gas analyzation. The primary objective is:

• To determine if early prehospital applied NIV together with standard medical treatment will affect arterial pH at hospital arrival in patients with ARF due to AECOPD.

Participants in the intervention will receive Non-invasive ventilation together with standard medical treatment. The intervention will be compared to standard medical treatment alone, that may include inhaled bronchodilators, intravenous corticosteroids, and titrated oxygen supplementation.

Inclusion Criteria:

1. Age greater than or equal to 18 years.

2. Medical history of COPD.

3. Unable to give informed consent ("Inhabil" in Danish) based on the criteria below

4. Respiratory acidosis with a PaCO2 of > 6,0 kPa and a pH of < 7,30.

   And one of the following:

5. Respiratory rate of > 25 per minute.

6. Hypoxia with a PaO2 < 7 kPa and/or a saturation < 88% without oxygen administered.

Exclusion Criteria:

1. Upper gastrointestinal hemorrhage or vomiting.
2. Anatomical abnormality that precludes the use of an oro-nasal interface.
3. Suspicion of pneumothorax.
4. Cardiac or respiratory arrest.
5. Uncontrollable malignant arrhythmia.
6. Refractory shock (systolic blood pressure < 90 mmHg) despite fluids and/or vasoactive drugs given.
7. Required orotracheal intubation.
8. Suspected upper airway obstruction.
9. No indication for life-prolonging treatment with NIV.

Six months after the publication of the last results, all de-identified individual patient data will be made available for data sharing. Procedures, including re-coding of key variables, will be put in place to allow for complete de-identification of the data. Data will be completely anonymized according to Danish law.

All relevant trial-related documents, including the protocol, data dictionary, and the main statistical code, will be shared along with the data.

There will be no predetermined end date for the data sharing.

Data will be available for any research purpose to all interested parties who have approval from an independent review committee and who have a methodological sound proposal as determined by the steering committee of the current trial. Only the methodological qualities and not the purpose or objective of the proposal will be considered. Interested parties will be able to request the data by contacting the principal investigator. Authorship of publications emerging from the shared data will follow standard authorship guidelines from the International Committee of Medical Journal Editors and might or might not include authors from the steering committee depending on the nature of their involvement.

Due to the nature of the intervention, the clinicians performing the intervention cannot be blinded. This is also the case for patients along with any legally designated representatives at the scene. As it is common to note the prehospital treatment in the patient's medical records clinicians at the ED and/or ICU will not necessarily be blinded either. For the same reason, investigators involved in data entry will also not be blinded meaning that outcomes such as change in arterial pH are entered without blinding. However, there is little - if any - subjectivity in evaluating these outcomes and blinding is therefore likely of minor importance.

A patient - or alternatively the consenting legally designated representatives - will not be informed of the allocation until the end of follow-up and only per request on the consent form.