At hour 6 , tolerance to cutaneous stimulation for limbs receiving 0.1 % ropivacaine was [ mean ( standard deviation ) ] 27.0 ( 20.2 ) vs26 .9 ( 20.4 ) mA for limbs receiving 0.4 % [ estimated mean difference 0.2 mA ; 90 % confidence interval ( CI ) -8.2 to 8.5 ; P = 0.02 and 0.03 for lower and upper boundaries , respectively ] .