METHODS	After an i.v. loading dose ( 100 microg kg ( -1 ) ) , morphine infusions [ 23-26 weeks postmenstrual age ( PMA ) 10 microg kg ( -1 ) h ( -1 ) ; 27-29 weeks 20 microg kg ( -1 ) h ( -1 ) ; and 30-32 weeks 30 microg kg ( -1 ) h ( -1 ) ] were established for a maximum of 14 days .\