In order to determine the speed of onset of the anaesthetic propofol in children, investigators will compare the two age groups 1-6 years vs 8-13 years. The primary outcome measure is the time to peak effect of a bolus of proposal, which is measured by analysing the electroencephalogram by using the permutation entropy. Further pharmacodynamic modelling will enable investigators to quantify the difference with age in the hypnotic effect of propofol.

Inclusion Criteria:

• The study population will be healthy children in the ranges of 1-6 and 8-13 years of age having surgery with American Society of Anaesthesia (ASA) grades I-II (ie. no prior functional limitation due to comorbidities) that fulfil the following points:
• parental written consent obtained at least a day prior to begin of the subject's study episode; and
• the child is appropriate for induction and maintenance of anaesthesia with propofol.

Exclusion Criteria:

• Any significant subject co-morbidity (ASA III or IV);
• Withdrawal of consent/assent at any point in the study;
• Failure to cannulate a peripheral vein prior to induction after two attempts;
• Any other reason making IV induction with propofol impossible;
• Allergy to propofol (or its emulsion carrier), Eutectic Mixture of Local Anesthetics (EMLA) cream or Nitrous Oxide (N2O);
• previous enrolment in the study;
• Any anaesthetic problem that would take precedence over completion of the study protocol.

The analysis of the electroencephalogram will be blinded to the age of the participant.