2 ug/kg of intranasal dexmedetomidine could produce satisfactory sedation in more children for ophthalmic examinations than the sedative effect of 1ug/kg.

Dexmedetomidine is an a2-adrenergic receptor agonist that provides sedation without respiratory depression.Clinical trials have demonstrated that intranasal dexmedetomidine in a dose of 1ug/kg produces satisfactory sedation in between 53% and 57% of children at anaesthetic induction. There are also reports using higher doses of intranasal dexmedetomidine. The investigators compared the sedative effect of 1ug/kg intranasal dexmedetomidine with those of 2 ug/kg for ophthalmic examinations in children aged 2 months-10 years and hypothesised that the higher dose would produce satisfactory sedation in more children at the time of anaesthetic induction.

Inclusion Criteria:

• Need sedation for ophthalmic examinations
• Children who had failed chloral hydrate sedation, i.e.there was no evidence of sedation 30 min following administration.
• With informed consent from parents

Exclusion Criteria:

• Children with gastroesophageal reflux
• Children with nausea and vomiting
• Children with apnea in the past three months
• Children with recent pneumonia, exacerbation of asthma, bronchitis and upper respiratory tract infection
• Children with severe arrhythmias, heart failure and cardiac structural abnormalities
• Children with facial abnormalities, who is expected to be difficult with effective mask ventilation
• Children with severe neurological disease
• Children with moyamoya disease
• Children who is allergy to For dexmedetomidine or chloral hydrate
• Preterm children, weight <2 kg