ACUTE TRIAL: Ambulance CPAP: Use, Treatment effect and Economics

Frequently Asked Questions

How many litres can the CPAP mask be used at, and will we have enough oxygen available to do this?

You will receive training in use of the CPAP mask prior to recruiting patients into the trial. The O_Two CPAP device is connected to a normal oxygen flow regulator, either in the ambulance or a portable oxygen cylinder. After attaching oxygen tubing to oxygen flow meter and CPAP mask the flow rate is adjusted initially to 8 litres/min. In response to the patient’s clinical condition the flow rate can be increased every 3-5 minutes, up to a maximum of 25 l/min. Target saturations are 88-92% in COPD and >94% in other conditions. The table below details the inspired oxygen concentration and degree of CPAP for the O-Two device achieved at different flow rates:

Flow rate (l/min) / 8 / 10 / 12 / 15 / 20 / 25
CPAP achieved (cmH2o) / 5 / 8 / 10 / 15 / 18 / 20
Inspired Oxygen concentration (%) / 45 / 50 / 55 / 65 / 70 / 75

Ambulances contain 7,930 litres of oxygen and even at maximal flow rates of 15 l/min oxygen supplies would last over 9 hours. CD size portable oxygen cylinders contain 610 litres of oxygen and would last 40 minutes at 15 l/min.

Can nebulizers be given with the o_two CPAP device?

Yes, nebulizer treatments (salbutamol or Ipratropium bromide) can be given concurrently without affecting the CPAP performance. The nebulized medication is administered by inserting the nebulizer “T” piecebetween the CPAP facemask and connecting this to a second oxygen flow regulator at 6 l/min. Adjustment of the CPAP level and inspired oxygen concentration is achieved as described above. Gas consumption and cylinder duration will be

minimally affected by additional use of a nebulizer.

Can sublingual GTN be given while using the o_two CPAP device?

Yes. Patients’ with acute respiratory failure caused by acute cardiogenic pulmonary oedema, or with chest pain, may require additionally treatment with sub-lingual GTN. The lower straps of the CPAP harness can be removed and the lower half of the CPAP mask lifter to provide access to the mouth. After using the GTN the mask should be replaced and re-attached to ensure an air-tight seal.

Can we use this on someone who has their own CPAP at home?

Although rare, an increasing number of patients are treated with home CPAP for chronic respiratory disease, or use nocturnal CPAP for obstructive sleep apnoea. If a patient is actively using their own CPAP machine on initial assessment they should not be enrolled into the trial. Treatment should continue according to the EMS provider’s judgement and usual protocols. If the patient is not actively using their own CPAP machine they are eligible for the trial providing they meet other enrolment criteria.

Can we use this on someone who has a tracheostomy?

Occasionally patients may present in acute respiratory failure who have a tracheostomy. It is not possible to obtain an adequate CPAP mask seal in such patients and they should not be enrolled in the trial in accordance with the exclusion criterion ‘anticipated inability to apply CPAP’.

Can patients with acute respiratory failure secondary to drowning be included?

Yes, any patient with acute respiratory failure meeting the trial inclusion and exclusion criteria can be included. Acute respiratory failure will commonly be caused by COPD, pneumonia or acute heart failure; but other rarer causes such as drowning are eligible.

Can I give CPAP to patients with a decreased level of consciousness?

CPAP can be safely given to patients who are not fully alert. However, in patients with a very low GCS<9 protective airway reflexes may be absent and there could be a risk of aspiration if the patient vomits.

What should I do if I think a patient should not be included in the trial but they meet all of the inclusion/exclusion criteria?

The main aim of the ACUTE pilot is a pilot study to see if it is safe and feasible to proceed to a larger definitive study. There may be important exclusion criteria that we haven’t thought of. If you treat a patient that is otherwise eligible for the trial, but you feel that there is a special circumstance why they should not be included, please do not enrol the patient in the study. We would be very grateful if you could contact the clinical support desk to register the patient as a non-recruited case and provide details about why they weren’t suitable for the trial.

What actions need to be taken if someone has CPAP applied and then is not transported to hospital?

To be eligible for CPAP in the ACUTE trial a patient must be hypoxic despite supplemental oxygen:

  • <88% in patients with COPD despite low flow oxygen
  • <94% in other patents despite high flow oxygen

It is unlikely that such patients would not be transported to hospital after receiving CPAP treatment. However, in the contingency that a patient is enrolled in the trial, randomised to CPAP treatment and is not conveyed, normal trial procedures should be followed. This would entail completing the ambulance case report form and phoning the clinical support desk to register the enrolled patient and submit data.

What is the frequency of adverse events for CPAP used in a pre-hospital setting?

Prehospital CPAP has been introduced in a number of emergency medical services in the United Kingdom and worldwide. Adverse events are uncommon. A recent study of 171 patients from Denmark reported that 3 patients (1.75%) treated with CPAP required discontinuation of treatment due to an adverse event. These were hypotension, decreased level of consciousness and a possible pneumothorax.

How common is tension pneumothorax as an adverse event associated with CPAP?

Tension pneumothorax is a very rare complication of prehospital CPAP. A single case has been reported in the worldwide literature. The trial inclusion criteria have been designed to minimise this small risk further. In the unusual event of a tension pneumothorax occurring, CPAP should be discontinued and a needle decompression performed. If treated by an ambulance technician, they should follow their normal procedure for managing such patients including calling for additional paramedic backup.

Is it true that all patients who receive in Hospital CPAP undergo prophylactic chest drains?

No. Chest drains would not be placed for patients who receive CPAP in hospital, unless there was another specific indication e.g. a large pleural effusion.

Why are patients with DNACPR forms excluded?

DNACPR forms are commonly completed for patients suffering from advanced frailty, co-morbidity, or progressive irreversible disease. They are an important mechanism for protecting patients from harm; but DNACPR decisions should not be conflated with end-of-life care, and such forms do not mean that other treatments should not be given. Clinical management decisions are often challenging in these contexts and should be made on an individual basis, determined by the patient's condition, wishes and beliefs. Given this complexity, an independent ethics committee felt that patients who have an advanced DNACPR decision would not be considered suitable for research studies in an emergency setting where patients are enrolled in a time pressured environment, often without initial

consent due to lack of capacity according to the provisions of the 2005 Mental Capacity Act. Our public and patient advisory group also requested that such patients should not be included.

What if I have any other questions?

Further information about the trial can be found on the trial website: This includes training modules and links to additional educational resources. Please do not hesitate to ask any questions regarding the ACUTE trial to the study research paramedics:

Josh –

Imogen -

ACUTE TRIAL: Ambulance CPAP: Use, Treatment effect and Economics