A Post-Approval Multicenter Study to Assess the Continued Safety and Effectiveness of the AeroPace® System

Inclusion Criteria: 1. Are 18 years or older, and, 2. Will have been mechanically ventilated for ≥96 hours (4 days) by the time of Catheter insertion, and, 3. Have not weaned from MV, and, 4. Have failed an institutional SBT within 48 hours of enrollment. Exclusion Criteria: 1. Invasive mechanical ventilation \>90 days. 2. Currently on extracorporeal membrane oxygenation (ECMO). 3. Weaning failure due to hypervolemia. 4. Medical history (including imaging) or known anatomy that prevents percutaneous insertion of the Catheter into the intended thoracic vein on the left side. 5. Clinically overt congestive heart failure that is preventing weaning. 6. Currently being treated with neuromuscular blockade that could affect phrenic nerve / diaphragm contraction. 7. Pre-existing neurological, neuromuscular or muscular disorder that could affect the respiratory muscles. 8. Pre-existing severe chronic pulmonary fibrosis. 9. Known pleural effusions occupying greater than one third of the pleural space on either side. 10. BMI \>70 kg/m2. 11. Known or suspected phrenic nerve paralysis. 12. Any electrical device (implanted or external) that may be prone to interaction with, or interference from the AeroPace System, including neurological pacing/stimulator devices, cardiac pacemakers and defibrillators. 13. Current hemodynamic instability 14. Uncontrolled sepsis or septic shock. 15. Current or untreated bacteremia. 16. Expecting withdrawal of life support and/or shift to palliation as the goal of care. 17. Known or suspected to be pregnant or lactating. 18. Currently being treated in another clinical trial studying an experimental treatment that could affect the study primary outcome.