 1. To demonstrate non-inferiority of analgesia with intrathecal morphine 0.3mg compared to continuous epidural analgesia with 8 mlhour of mixture of bupivacaine 0.125 and sufentanil 0,4ugml. Non-inferiority is defined as consumption of PCA morphine during 24 and 72 hours not higher than 10 compared to control group. 