Study not undertaken due to COVID and capacity

This study evaluates the effect of airway pressure release ventilation (APRV) on lung homogeneity and recruitment in patients with moderate to severe acute respiratory distress syndrome (ARDS).

It will do this by comparing the homogeneity of ventilation and recruitment prior to a patient being ventilated on APRV, and at 30, 60 and 120 minutes after starting APRV.

Ventilator-induced lung injury (VILI) is a well-recognised problem of ventilation in patients with ARDS, and is currently treated with lung-protective ventilation, which limits tidal volumes and airway pressures by applying higher levels of positive-end expiratory pressure (PEEP). However, it is not known whether higher levels of PEEP increases recruitment and homogeneity of ventilation within the lungs.

APRV is a mode of inverse ventilation, where high levels of PEEP are maintained with brief releases of pressure, and has been proposed as an appropriate method of ventilation in patients with ARDS.

This study will assess homogeneity of ventilation and recruitment in 15 patients before APRV is started, and 30, 60 and 120 mins after commencing APRV. It will do this using Electrical Impedance Tomography (EIT), nitrogen wash in/wash out technique, and lung strain.

Inclusion Criteria:

• Age ≥ 18 years and < 80 years

  • Weight > 35 Kg and BMI < 40
  • Informed consent according to local regulations
  • Hemoglobin ≥ 70 g/dl
  • Haemodynamically stable > 4 hours
  • Moderate to severe ARDS (PaO2/FIO2 < 26.6 kPa with positive end-expiratory pressure (PEEP) > 5 cmH2O) as per Berlin definition of ARDS

Exclusion Criteria:

• Expected survival < 72 hours

  • Suspected pregnancy (negative pregnancy test required for women of child-bearing potential)
  • Open abdomen
  • Documented or suspected raised intracranial pressure
  • Active air leak (pneumothorax, pneumomediastinum, subcutaneous emphysema)
  • Morbid obesity BMI > 40
  • Recent < 1 week cardiac or thoracic surgery
  • Unstable thorax and sternum with paradoxical chest wall movement
  • Severe Chronic Respiratory Disease (COPD) - GOLD 3 or 4 emphysema with bullae
  • Severe smoking (> 40 pack-year history)
  • Liver Failure: Child-Pugh Class C
  • Massive ascites
  • Lung fibrosis
  • Severe cardiac disease (one of the following): New York Heart Association Class III or IV, acute coronary syndrome or persistent ventricular tachyarrhythmias
  • Sickle cell disease

All Patients admitted to ICU ventilated with moderate or severe ARDS, based on the Berlin definition of ARDS.

All shared data will be as a mean and not as individual