After induced with sevoflurane , a loading dose of PRO ( 2 mgkg ( -1 ) ) was administrated and followed by continuous infusion ( 200 gkg ( -1 ) min ( -1 ) ) ; a loading dose of DEX ( 2 gkg ( -1 ) ) was administrated and followed by continuous infusion ( 2 gkg ( -1 ) h ( -1 ) ) .