Children up to the age of 16 years requiring MRI under deep sedation with at least 3 characteristics of respiratory morbidities were identified as having increased risk for adverse respiratory events. Dexmedetomidine was administered as a first bolus of 1 mcg•kg-1 over 10 min, followed by a continuous infusion at 1.0 mcg•kg-1•h-1. Sedation level was assessed by Ramsay Sedation Scale and it was initially recorded at 1-min interval. If the child failed to achieve a minimum RSS of 5, this bolus was repeated once again and the continuous infusion was subsequently increased to 2 mcg•kg-1•h-1. In addition, propofol 0.5 mg.kg-1 iv. was allowed to be administered, in patients still exhibiting movement that could interfere with image acquisition.

completion of imaging without requirement for rescheduling or general anaesthesia, and in the absence of adverse respiratory events such as apnoea, cough, oxygen desaturation, and bronchospasm or unplanned escalation of care (e.g. transfer from ward to paediatric intensive care unit or prolonged hospitalization).

Based on age-adjusted criteria, bradycardia was defined as a HR <20% below the lower limit of the normal ranges expressed in beats/min