This registry was proposed to investigate the epidemiology of respiratory mechanics in patients with ARDS through collecting data from a QI project which was constituted with systematic assessments of respiratory mechanics and gas exchange.

The amount of respiratory impairment in patients with Acute Respiratory Distress Syndrome (ARDS) is variable and applying the same ventilator regimen to every patient is questionable. In order to individualize ventilator management, monitoring respiratory mechanics may help to decide ventilator settings or set limits. A systematic assessment of respiratory mechanics and gas exchange response in patients who meet the criteria for ARDS has been initiated as a Quality Improvement (QI) project in the Department of Critical Care at St. Michael's Hospital. The QI project aims to facilitate the use of these parameters for ventilatory management. Measurements include: respiratory system, lung and chest wall mechanics (elastance and resistance), oxygenation response to positive end-expiratory pressure (PEEP), and estimate of alveolar recruitability using a simplified bedside maneuver[1]. Placement of an esophageal catheter is considered when the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2) ≤200 mmHg[2]. Audits are performed to see whether the measurements influence ventilatory management. Collecting these data into a registry will elicit helpful epidemiological information since the current epidemiological knowledge surrounding respiratory mechanics abnormalities in ARDS is limited. A registry with a large sample size may inform future recommendations. The investigators therefore propose to introduce the collected data from our QI program into an ARDS registry. Similar data obtained from other centers may also contribute to the registry in the future. The primary objective of the registry will be to investigate the epidemiology of abnormal respiratory mechanics in patients with ARDS.

Inclusion Criteria:

• All patients admitted to the Medical-Surgical ICU, Trauma-Neuro ICU, and Cardiovascular ICU who meet the Berlin definition of ARDS and receive invasive ventilation.

Exclusion Criteria:

• Severe hemodynamic instability: > 30% variation of mean arterial pressure and/or heart rate (HR) in the last 2 hours or the need for a high dose of vasopressors (higher than 0.5 µg/kg/min of norepinephrine);
• Patients who present with a known esophageal problem, active upper gastrointestinal bleeding, or any other contraindication for the insertion of a gastric tube.

All patients who have performed the ARDS pulmonary function test will be eligible for the registry. The clinical team discuss on a case-by-case basis to determine whether an ARDS patient is appropriate to received the ARDS pulmonary function test (systematic assessment of respiratory mechanics in the QI portion)