Double-blind randomized study on patients undergoing thoracotomy allocated to one of the following : group Kiv ( IV racemic ketamine 0.5 mg/kg preincisional +0.25 mg/kg/h for 48 h ) , group Kep ( epidural racemic ketamine 0.5 mg/kg preincisional +0.25 mg/kg/h for 48 h ) , or group S ( saline ) .