At 1-month follow-up , 19 of 140 patients in the dexamethasone group ( 13.6 % ) and 10 of 138 patients in the placebo group ( 7.2 % ) fulfilled the diagnostic criteria for POCD ( relative risk , 1.87 ; 95 % CI , 0.90 to 3.88 ; P = 0.09 ) .