The addition of PEEP did not have any measurable effect on the surgical field scores after onset of surgery ( odds ratio [ OR ] ( 95 % confidence interval [ CI ] ) = 1.06 ( 0.44-2 .58 ) , P = 0.895 for side 1 ; OR ( 95 % CI ) = 0.56 ( 0.16-1 .93 ) , P = 0.356 for side 2 ) .