Acute respiratory distress syndrome (ARDS) is a common and catastrophic complication of critical illness related to burns, motor vehicle accidents, or overwhelming infection. ARDS kills 40-70% of affected patients. Patients with ARDS require life support in the form of a ventilator to breathe for them while their lungs heal. Ironically, ventilators can cause further damage to the lungs. We are conducting a study comparing 2 methods to protect the lungs from further damage. One method uses standard mechanical ventilators and the other uses a new type of ventilator, called a high frequency oscillator. We propose to test whether this high frequency oscillation will reduce the relative risk of dying from ARDS. 72 patients from 12 intensive care units in Canada and Saudi Arabia will participate in this preliminary study to test the feasibility of our study methods. If feasible, we plan to move on and conduct a large multinational study to definitively answer this question.

Inclusion Criteria:

• Patients of either sex, 16 years and above;
• Acute onset of respiratory failure, with fewer than 2 weeks of new pulmonary symptoms;
• Endotracheal intubation or tracheostomy;
• Hypoxaemia - defined as a PaO2/FiO2 ≤ 200 mm Hg;
• Bilateral alveolar consolidation (airspace disease) seen on frontal chest radiograph

Exclusion Criteria:

• Remaining duration of mechanical ventilation < 48 hours, as judged by the attending physician;
• Primary cause of acute respiratory failure judged by attending physician to be cardiac in origin;
• Lack of commitment to ongoing life support;
• Weight < 35 kg;
• Severe chronic respiratory disease
• Morbid obesity - defined as > 1 kg / cm body height;
• Neurological conditions with risk of intracranial hypertension (hypercapnia should be avoided);
• Neuromuscular disease that will result in prolonged need for mechanical ventilation;
• Previous enrolment in this trial;
• All inclusion criteria present for > 72 hours;
• On HFO at the time of screening.