Pharmacokinetics and Pharmacodynamics of Dexmedetomidine in Pediatrics Subjects

Inclusion Criteria: * Initially intubated and mechanically ventilated pediatric subjects in an intensive care setting anticipated to require a minimum of 6 hours of continuous intravenous sedation. * Age: subjects must fit into one of the following age ranges at screening: * ≥2 years old through \<6 years old * ≥6 years old through \<17 years old * If female, subject is non-lactating and is either: 1. Not of childbearing potential, defined as pre-menarche, or surgically sterile due to bilateral tubal ligation, bilateral oophorectomy or hysterectomy. 2. Of childbearing potential but is not pregnant at time of baseline. * Subject's parent(s) or legal guardian(s) has/have voluntarily signed and dated the informed consent document approved by the Institutional Review Board. Assent will be obtained where age-appropriate and according to state regulations. Exclusion Criteria: * Pediatric subjects with neurological conditions that prohibit an evaluation of sedation * Diminished consciousness from increased intracranial pressure. * Extensive brain surgery (surgery requiring intracranial pressure monitor). * Diminished cognitive function per PI's discretion. * Subjects with immobility from neuromuscular disease or continuous infusion of neuromuscular blocking agents. * Weight \<10 kg. * Subjects with second degree or third degree heart block unless subject has a pacemaker or pacing wires. * Hepatic impairment Serum glutamic pyruvic transaminase/Alanine aminotransferase (SGPT/ALT) \>100 U/L * Hypotension based on repeat assessments prior to starting study drug: * Age ≥2 years old through ≤12 years old: systolic blood pressure (SBP) \<80 mmHg * Age \>12 years old through \<17 years old: SBP \<90 mmHg * Pre-existing bradycardia prior to starting study drug defined as: * Age ≥2 years old through ≤6 years old: ≤70 beats per minute (bpm) * Age \>6 years old through ≤12 years old: ≤60 bpm * Age \>12 years old through ≤16 years old: ≤50 bpm * Acute thermal burns involving more than 15 percent total body surface area. * Subjects who have a known allergy to dexmedetomidine, midazolam (MDZ) or fentanyl. * Subjects with a life expectancy that is \<72 hours. * Subjects that are expected to have hemodialysis (continuous hemofiltration) or peritoneal dialysis within 48 hours. * Subjects who have been treated with α-2 agonists/antagonists within two weeks. * Subjects with a spinal cord injury above T5. * Subjects who have received another investigational drug within the past 30 days. * Subjects on nicotine replacement therapy. * Subjects who, in the opinion of the investigator, may not be able to comply with the safety monitoring requirements of this clinical study.