There was no significant reduction in propofol requirements after the administration of 0.5 mg/kg lidocaine from 8.5 g/ml [ confidence interval ( CI ) 6.0-11 .625 ] to 8.25 g/ml ( CI 6.75-9 .76 ) ; however , a bolus of 1.5 mg/kg lidocaine decreased the Cp50 value of propofol by 42 % from 8.5 g/ml ( CI 6.0-11 .625 ) to 4.92 g/ml ( CI 4.5-5 .78 ) ( P < 0.05 ) .