After approximately 60 minutes , a dexmedetomidine infusion was started ( 0.25 g kg ( -1 ) then 1.0 g ( -1 ) kg ( -1 ) hour ( -1 ) ) in combination with either saline ( group S ) , morphine ( 0.15 mg kg ( -1 ) then 0.1 mg kg ( -1 ) hour ( -1 ) ; group M ) , or remifentanil ( 6.0 g kg ( -1 ) hour ( -1 ) ; group R ) for 60 minutes .