Phase 1, Children received a bolus of intranasal dexmedetomidine which adjusted by the "Dixon up-and-down method for TEE study. The first child received 2.5 mcg/kg of intranasal dexmedetomidine dose (100mcg/ml), and the dose varied by 0.1 mcg/kg according to the up-and-down method Phase 2 was a dose-escalation study. After interim analysis of the phase 1 results, four dose levels above the calculated ED50 were defined. Dose spacing was set at 0.25 mcg/kg of intranasal dexmedetomidine consistent with the re-estimated standard deviation (SD).

Phase 1: The starting dose of dexmedetomidine was 2.5 mcg/kg. These doses varied by 0.1 mcg/kg, according to the up-and-down method 18. If the detected MOAA/S score was >3 within 45 minutes after intranasal administration, or clinically adequate diagnostic-quality images could not be acquired, sedation was considered a failure; and the dexmedetomidine dose was increased by 0.1 mcg/kg in the next patient of the same age group. In contrast, if the detected MOAA/S score was ≤3 and the acquisition of clinically adequate diagnostic-quality images was possible, the sedation was considered successful; and the dexmedetomidine dose was decreased by 0.1 mcg/kg in the next patient o

Phase 2 was a dose-escalation study. After interim analysis of the phase 1 results, four dose levels above the calculated ED50 were defined. Dose spacing was set at 0.3 mcg/kg of intranasal dexmedetomidine consistent with the re-estimated standard deviation (SD). Defined levels were set at about 2.5, 2.75, 3.0, and 3.25 mcg/kg of intranasal dexmedetomidine. Criteria for success and failure were identical to those in phase 1.

Successful sedation was defined as a MOAA/S score between 0-3 and allowed the acquisition of clinically adequate diagnostic-quality images, while failure was defined as a MOAA/S score >3 within 45 minutes or clinically adequate diagnostic-quality images could not be acquired

Movement score was recorded by sonographers who were blinded to the sedative regimen.

1. No movement
2. Occasional, slight movement
3. Frequent, slight movement
4. Vigorous movement limited to extremities
5. Vigorous movement, including torso and head

Successful sedation was defined as an MOAA/S of between 0 and 3, and sedation induction time was defined as the time from drug administration to the onset of satisfactory sedation

Bradycardia was defined as a reduction in heart rate more than 20% from the baseline values

Significant Oxyhemoglobin desaturation was defined as < 90%.