Sedation MRI - Propofol Versus Propofol-Ketamin in Children

Children \< 10 years of age often need deep sedation or anaesthesia to allow elective diagnostic magnetic resonance imaging; standard routine protocols are 1. propofol induction without other sedative (Propofol much as needed) or hypnotic drugs and propofol infusion 10 mg/kg h 2. propofol induction with ketamine 1 mg /kg (little repetitive Propofol doses as needed) and propofol infusion 5 mg / kg h both protocols are compared with regard to clinical outcome and, in cases with cerebral MRI, cerebral perfusion/blood flow. Hypothesis: 1. reduces recovery time compared to propofol mono sedation 2. combination of ketamine-propofol increases incidence of Postoperative nausea and vomiting (PONV) compared to propofol mono sedation 3. combination of ketamine-propofol increases global cerebral blood flow and changes regional distribution of cerebral perfusion compared to propofol mono sedation