PAV vs Assist Control After Failed SBT

The primary aim of this research is to determine the feasibility of conducting a randomized controlled trial comparing two ventilation modes in patients admitted to the ICU who require mechanical ventilation. The investigators plan to include patients on mechanical ventilation with low support (PaO2/FiO2 ratio \> 200, FiO2 \< 0.5 and PEEP \< 8) for a period no longer than 48 hrs. There are a number of potential barriers to enroll patients in the study. Importantly patients will have to be enrolled within 48 hours from the time they meet inclusion criteria. The secondary aims are to determine the impact of proportional assist-ventilation (PAV) versus volume assist-control (VAC) ventilation by evaluating the number of ventilation-free days, development of Intensive Care Unit (ICU) delirium, use of sedative/ analgesic medications, use of antipsychotic medications, length of stay in the intensive care unit and hospital, reintubations within 24 hours, adverse events, and mortality in the two groups of patients.