METHODS	One hundred patients undergoing gynaecologic laparoscopic surgery were randomly assigned to one of four groups : conventional inspiratory-to-expiratory ( I : E ) ratio ( Group 1 : 2 ) , I : E ratio of 1 : 1 ( Group 1 : 1 ) , 2 : 1 ( Group 2 : 1 ) , or 1 : 2 with external positive end-expiratory pressure ( PEEP ) of 5 cmH2 O ( Group 1 : 2 PEEP ) .\