The aim is to test a device for applying continuous negative abdominal pressure in patients with ARDS

Adult respiratory distress syndrome (ARDS) is a serious pulmonary disease affecting adults and children. It has a high mortality and there is no specific therapy. The mortality is high (approx. 40% in severe cases) and this has not changed in the last 20 years.

Mechanical ventilation is the mainstay of management, and this assists the patient by increasing oxygenation and removal of carbon dioxide. Despite optimizing tidal volume, driving pressure and positive end-expiratory pressure (PEEP), patients with ARDS develop large areas of atelectasis and poor oxygenation. There are few additional ventilator approaches that have proven to be useful in preventing this type of injury.

A major aim of ventilator support is recruitment of atelectatic (i.e. de-airated) lung, but while this is supported by excellent rational and laboratory data, the conventional clinical approaches have not been associated with a demonstrable improvement in patient outcome. Most atelectasis in ARDS occurs in the dorsal (dependant, lower-most) lung regions, and these are near the diaphragm.

The main ways to recruit lung are to increase the airway distending pressure (but this over-expands and damages the already-aerated lung regions); or, to turn the patient into the prone position (but clinicians are reluctant to utilize this approach - despite evidence that it may increase survival).

Continuous Negative Abdominal Pressure (CNAP) aims to selectively recruit basal atelectatic areas of lung, while enabling the patient to remain in the supine (usual) position.

Inclusion Criteria:

1. Patients ≧ 18 years old
2. Patients with moderate to severe ARDS as per the Berlin definition (PaO2/FiO2 ≤200mmHg)
3. Patients with absence of any significant cardiopulmonary disease

Exclusion Criteria:

1. Contraindication to CNAP

   a. open abdominal wounds or drainage tubes; b. Acute brain Injury with intracranial pressure >30 mm Hg or cerebral perfusion pressure <60 mmHg; c. Decompensated heart insufficiency or acute coronary syndrome; d. Major hemodynamic instability: Mean arterial pressure lower than 60 mm Hg despite adequate fluid resuscitation and two vasopressors or increase of vasopressor dose by 30% in the next 6 hours; f. Unstable spine, femur, or pelvic fractures; g. Pregnancy; h. Pneumothorax;

2. Contraindication to EIT electrode placement: Burns, chest wall bandaging limiting electrode placement

3. Severe liver insufficiency (Child-Pugh score > 7) or fulminant hepatic failure

4. Major respiratory acidosis or PaCO2 > 60 mmHg

5. Severe COPD (according to the GOLD criteria defined as severe = FEV1: 30-50% or very severe = FEV1 < 30%)

6. Clinical judgement of the attending physician

undecided