This study investigates under controlled conditions the variation of poorly ventilated lung units (silent spaces) in children between 1 and 6 years of age measured by electrical impedance tomography during intravenous anaesthesia in a day-hospital setting and before discharge to help further raise safety standards in paediatric anaesthesia

Eligible, children, with parental written informed consent, scheduled for a cerebral magnetic resonance image (MRI) will receive an intravenous anaesthesia using a Propofol infusion of 10 mg/kg/h. At the Bern Children's Hospital all children will be premedicated with Midazolam rectal/oral 0.5 mg/kg or Dexmedetomidine nasal 2 mcg/kg 20 minutes before the beginning of the procedure Eligible children will be prepared for procedure according to the local SOPs of the paediatric anaesthesia departments. Mandatory monitoring will consist of: SpO2, HR, NIBP. An iv-line for drugs injection will be placed.

Induction of anaesthesia: after iv-line placement a bolus of Propofol of 2 mg/kg followed by a continuous infusion of 10 mg/kg/h will be applied. Administration of low-flow oxygen for all children (0.3 l/kg/min) via Microstream® Smart CapnoLine® paediatric cannula (Philips Healthcare, Amsterdam, Netherlands). This cannula allows to measure the etCO2.

In case of extremely agitated child an inhalative induction may be performed. This technique represent the actual standard of care and is not associated with increased risks because of the study.

Before induction of the anaesthesia, before the radiological procedure when the induction is terminated, after the termination of the radiological procedure, before transport to the Post anaesthesia Care Unite (PACU), and before the discharge from the PACU after 2 hours of monitoring ventilation distribution changes by thoracic electrical impedance tomography are measured (each measurement will last 1 min).

Inclusion Criteria:

• ASA physical status 1 to 3,
• 1 to 6 years of age with legal guardians providing written informed consent.

Exclusion Criteria:

• Exclusion criteria are necessity to intubate the child,
• contraindication for propofol administration,
• congenital heart or lung disease with oxygen
• dependency and high aspiration risk (requiring rapid sequence induction intubation).

We will include paediatric patients undergoing radiological procedures requiring intravenous anaesthesia.