Efficacy, Safety and Pharmacokinetic Study of Intravenous Clonidine Versus Midazolam for Sedation in Paediatric Patients

Inclusion Criteria: * Male or Female * Aged from birth (≥34 weeks gestational age \[GA\]) to \<17 years, 11 months, 1 week old * Admitted or expected to be admitted (post-operatively) to PICU * Existing or expected indication for invasive or non-invasive ventilation (except Continuous Positive Airway Pressure, CPAP) * Anticipated need for continuous sedation for at least 24 hours * Informed consent (or deferred consent) obtained from the subject's parent(s) or legal guardian(s) * Where applicable, assent obtained from the subject to participate in the clinical trial Exclusion Criteria: * Body weight less than 1500 g * Gestational age \[GA\] of \<34 weeks * Body weight 3 kg or less AND aged 28 days or older * Body weight less than 10 kg AND aged 2 years old or older * Body weight greater than 85 kg * Subjects who will be 18 years old in less than 3 weeks * Known hypersensitivity to the IMP (clonidine) or comparator (midazolam), or Non Investigational Medicinal Product (morphine, propofol) or any of their formulation ingredients and their rescue medication * Subjects anticipated to be treated with forbidden concomitant medications during IMP administration * Subjects less than 24 hours post-resuscitation * Subjects who have been under sedation for more than 72 hours immediately prior to assessment * Subjects currently being treated with Extra Corporeal Membrane Oxygenation (ECMO) * Subjects with treatment-induced whole body hypothermia * Subjects with severe organ insufficiencies * Subjects whose condition is assessed by the investigator to have an effect on the level of consciousness which impairs the assessment of sedation (COMFORT-B/NISS) * Subjects with phaeochromocytoma * Subjects with severe bradyarrhythmia resulting from either sick-sinus syndrome or atrioventricular (AV) block of 2nd or 3rd degree * Known arterial hypertension requiring chronic treatment in medical history * Females who are pregnant, lactating or planning to become pregnant or who return a positive result to a urine pregnancy test (a dipstick and serum pregnancy test will be performed at the screening visit). * Employee or direct relative of an employee or any member of the study site staff or the Sponsor/ study management staff (applies to subject and/ or subject's parent(s) * Participation in a clinical intervention study using drugs within the last 3 weeks * Previous participation in this clinical study at any time * Parent(s)/ legal guardian(s) decline to give informed consent. If parent(s)/ legal guardian(s) are not present