Diaphragm Injury and Dysfunction During Mechanical Ventilation

This study is designed to evaluate the relationship between diaphragm activity during mechanical ventilation and the development of ventilator-induced diaphragm dysfunction (VIDD). Diaphragm structure, activity, and function are monitored longitudinally over the first 7 days of mechanical ventilation.

Inclusion Criteria: * Adult patients (\>18) with acute respiratory failure receiving invasive mechanical ventilation for less than 36 hours diagnosed with any of the following conditions: acute severe brain injury; moderate or severe ARDS; septic shock; pneumonia Exclusion Criteria: * Predicted probability of remaining alive and on the ventilator on ICU day 7 is less than 50% * Liberation from mechanical ventilation is expected/planned within 24 hours * High cervical spine injury (C5 or higher) * Receiving mechanical ventilation for neuromuscular disease * Acute exacerbation of an obstructive lung disease * Known esophageal varices or any other condition for which the attending physician deems an orogastric catheter to be unsafe * Esophageal, gastric or duodenal surgical procedures within the last 6 months * Received mechanical ventilation for \> 48 hours in the preceding 6 months