The purpose of the study is to determine if 4mcg/kg of intranasal dexmedetomidine is better than 2mcg/kg in successfully sedating a child prior to induction of anesthesia.

Dexmedetomidine is a selective alpha-2 adrenoreceptor agonist that has sedative, anxiolytic and analgesic properties without causing respiratory depression. It has been administered safely and effectively via a number of routes including as an intravenous infusion, intramuscularly, intranasally, buccally and orally .

Yuen et al established that the median time of onset of sedation is 25-30 minutes, making it an ideal agent for preoperative sedation. The same group also studied doses of 1 mcg/kg and 2 mcg/kg as a sedative premedication and found that the success rates of appropriate sedation at induction in children aged 1 to 8 years were 53% and 66% respectively, with a dose related increase in successful sedation.

Much higher doses of dexmedetomidine have also been used safely. Administered intravenously, 3mcg/kg of dexmedetomidine has been shown to provide satisfactory sedation for paediatric MRI in 97% of cases, without adverse effects.

The investigators aim to show that high dose intranasal dexmedetomidine is a safe, effective and an easily administered sedative premedication.

The investigators hypothesise that 4mcg/kg compared to 2mcg/kg of intranasal dexmedetomidine will lead to at least a 20% increase in the proportion of satisfactorily sedated patients at the time of anaesthesia induction.

The primary outcome will be the proportion of children with satisfactory sedation at the time of anaesthesia induction.

Suitable patients will be identified from the theatre lists and consent will be sought from their legal guardians during preassessment clinic or during their anaesthetic preoperative assessment on the ward.

In a previous study, 66% of children aged 1-5 years were satisfactorily sedated at the time of induction with 2 mcg/kg of intranasal dexmedetomidine. In order to find a 20% difference with 4 mcg/kg of dexmedetomidine, the investigators' sample size needs to be 140 (70 in each group), for a power of 0.8 and a 5% false positive rate.

The demographic data will be analysed by t test and chi-square test. The proportions of satisfactory sedation will be analysed by chi-square test. The onset sedation time and duration of sedation will be analysed by survival analysis. The vital signs over times will be expressed by percentage changes from baseline and estimated by mean and standard errors. A p-value<0.05 will be considered statistically significant.

Inclusion Criteria:

• All children of American Society of Anesthesiologists (ASA) physical status classification I or II (healthy) between the ages of 6 months and 5 years undergoing surgery at Queen Mary Hospital

Exclusion Criteria:

• Any patient receiving other sedative premedication, allergy to dexmedetomidine, organ dysfunction, cardiac arrhythmia and congenital heart disease.