In Vietnam, Hoang Quoc Thang and et al. (2012) evaluated sedative effect of 0.25mcg / kg dexmedetomidine by intravenous route in colonoscopy procedure, recording the onset and duration of sedative time were 11 3.3 minutes and 37.2 6.9 minutes, achieved 3 sedative level on the Ramsay scale, equivalent to deep sleep but easy to wake up accounting for nearly 80%.