Inclusion Criteria

   1. Age > 18 years

   2. Presence of all of the following conditions for < 48 hours:

   i. PaO2/FiO2 < 150 with PEEP >/= 8 cm H2O OR, if ABG not available, SaO2/FiO2 ratio
   that is equivalent to a PaO2/FiO2 < 150 with PEEP >/= 8 cm H2O , and a confirmatory
   SaO2/FiO2 ratio that is again equivalent 1-6 hours later

ii. Bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules.

iii. Respiratory failure not fully explained by cardiac failure or fluid overload; need
objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk
factor present.

Patients must be enrolled within 48 hours of meeting inclusion criteria.

Exclusion Criteria:

   1. Lack of informed consent

   2. Continuous neuromuscular blockade at enrollment

   3. Known pregnancy

   4. Currently receiving ECMO therapy

   5. Chronic respiratory failure defined as PaCO2 > 60 mm Hg in the outpatient setting

   6. Home mechanical ventilation (non-invasive ventilation or via tracheotomy) except for
   CPAP/BIPAP used solely for sleep-disordered breathing

   7. Actual body weight exceeding 1 kg per centimeter of height

   8. Severe chronic liver disease defined as a Child-Pugh score of 12-15 (Appendix A2)

   9. Bone marrow transplantation within the last 1 year

10. Expected duration of mechanical ventilation of < 48 hours

11. Decision to withhold life-sustaining treatment; except in those patients committed to
   full support except cardiopulmonary resuscitation if an actual cardiac arrest occurs

12. Moribund patient not expected to survive 24 hours; if CPR provided, assess for
   moribund status greater than 6 from CPR conclusion

13. Diffuse alveolar hemorrhage from vasculitis

14. Burns > 70% total body surface

15. Unwillingness to utilize the ARDS Network 6 ml/kg IBW ventilation protocol

16. Previous hypersensitivity or anaphylactic reaction to cisatracurium

17. Neuromuscular conditions that may potentiate neuromuscular blockade and/or impair
   spontaneous ventilation (Appendix A2)

18. Neurologic conditions undergoing treatment for intracranial hypertension

19. Enrollment in an interventional ARDS trial with direct impact on neuromuscular
   blockade and PEEP

20. >120 hours of mechanical ventilation

21. P/F < 200 mmHg at the time of randomization (if available)