Effect & Safety of Inhaled Isoflurane vs IV Midazolam for Sedation in Mechanically Ventilated Children 3-17 Years Old

Inclusion Criteria: * Patients at least 3 years to 17 (less than 18) years at the time of randomization, admitted to an ICU/with planned ICU admission. * Expected mechanical (invasive) ventilation and sedation for at least 12 hours. * Informed consent obtained from the patient, patient's legal guardian(s) Exclusion Criteria: * Ongoing seizures requiring acute treatment. * Continuous sedation for more than 72 hours at time of randomization. * Less than 24 hours post cardiopulmonary resuscitation. * Uncompensated circulatory shock. * Known or suspected genetic susceptibility to malignant hyperthermia. * Patients with acute asthma or obstructive lung disease symptoms requiring treatment at inclusion. * Patient with tidal volume below 30 mL or above 800 mL. * Inability to perform reliable COMFORT-B assessment in the opinion of the Investigator * Patients with intracranial pressure (ICP) monitoring or with suspected increase in ICP * Patients with treatment-induced whole-body hypothermia. * Patients with pheochromocytoma. * Patients with prolonged QT interval or with significant risk for prolonged QT interval. * Patient not expected to survive next 48 hours or not committed to full medical care.