Inclusion Criteria:  Adult patients >18 years on mechanical ventilation and expected to need ventilatory support for the next 24 hours. Candidate for sedation and analgesia protocol  Exclusion Criteria:  Pregnant and/or lactating woman. Has been intubated for duration longer than 12 hours in an intensive care unit. Proven or suspected acute primary brain lesion such as traumatic brain injury, intracranial haemorrhage, stroke, or hypoxic brain injury. Proven or suspected spinal cord injury or other pathology that may result in permanent or prolonged weakness. Admission as a consequence of a suspected or proven drug overdose Mean arterial pressure (MAP) < 50 mmHg despite adequate resuscitation and vasopressor therapy at time of randomization. Death is deemed to be imminent or inevitable during this admission and either the attending physician, patient or substitute decision maker is not committed to active treatment. Patients with severe hepatic impairment (Child-Pugh class C) or end stage renal disease (ESRD) (creatinine clearance < 30 ml/min or on chronic hemodialysis) due to altered pharmacokinetics [20]. Need for deep sedation such as administration of neuromuscular blockers. Convulsions or previous history of convulsions. Risk of urinary retention linked to uretroprostatic disorders. Risk of acute angle glaucoma. Known intolerance of or hypersensitivity to study medications or constituents.