Inclusion Criteria:

- Adults ≥ 18 years of age;

- Patients who are anticipated to require >12 hours of invasive mechanical ventilation and continuous sedation in the ICU; and

- Receipt of continuous sedation due to clinical need for sedation to RASS < 0.

Exclusion Criteria:

- Need for RASS -5.

- Sedation for invasive mechanical ventilation immediately prior to Baseline for > 72 hours (patients who have been extubated for at least 24 hours and subsequently re-intubated will have sedation for invasive mechanical ventilation starting from when they were re-intubated); 

- Severe neurological condition that causes the patient to lack ability to participate in the study (i.e., unable to be assessed for RASS and Critical Care Pain Observation Tool), including, but not restricted to, patients with acute stroke, severe head trauma, meningitis, suspected of having elevated intracranial pressure (ICP), or the need for ICP monitoring;

- Ventilator tidal volume 1000 mL at Baseline;

- Need for extracorporeal membrane oxygenation, extracorporeal carbon dioxide removal, high frequency oscillation ventilation, or high frequency percussive ventilation at Screening;

- Comfort care only (end of life care);

Contraindication to propofol or isoflurane, including:

• Known or suspected personal or family history of malignant hyperthermia (MH) or high risk for MH or acute drug-induced muscle injury (e.g., muscular dystrophies);
• Severe hemodynamic compromise, defined as the need for norepinephrine ≥ 0.3 mcg/kg/min (or equivalent vasopressor dose) to maintain blood pressure within acceptable range, assumed to be mean arterial pressure ≥ 65 mmHg unless prescribed clinically; or
• Allergy to isoflurane or propofol, or have propofol infusion syndrome.

-  History of ventricular tachycardia/Long QT Syndrome;

-  Requirement of intravenous (IV) benzodiazepine or barbiturate administration for seizures or dependencies, including alcohol withdrawal;

- Neuromuscular disease that impairs spontaneous ventilation (eg, C5 or higher spinal cord injury, amyotrophic lateral sclerosis, etc);

- Concurrent enrollment in another study that, in the Investigator’s opinion, would impact the patient’s safety or assessments of this study;

- Participation in other study involving investigational drug(s) or devices(s) within 30 days prior to Randomization;

- Previous randomization or receipt of treatment in this study or in SED004;

- Anticipated requirement of treatment with continuous infusion of a neuromuscular blocking agent for > 4 hours;

- Female patients who are pregnant or breast-feeding;

- Imperative need for continuous active humidification through mechanical ventilation circuit;

- Attending physician’s refusal to include the patient; or

- Inability to obtain informed consent.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 12/15/23. Questions regarding updates should be directed to the study team contact.