Influence of Intraoperative Analgesia on the Postoperative Morphine Consumption

Unlike longer acting opiates (sufentanil), remifentanil may provoke postoperative hyperalgesia. We have developed two automated bispectral index - guided drug delivery systems: one for propofol administration, the other for combined propofol and remifentanil administration. Both systems achieve the same objective: similar level of anesthesia indicated by bispectral index levels between 40 to 60. We make the assumption that this method of automated remifentanil administration may avoid postoperative hyperalgesia. Patients scheduled for abdominal surgery will be divided into two groups: * in one group, patients will receive automatically delivered propofol and manually delivered sufentanil according to the usual criteria, * in the other group, patients will receive propofol and remifentanil both automatically administered. Assessment of postoperative hyperalgesia will be primarily based on morphine consumption (patient controlled analgesia) and detection of cutaneous hyperalgesia areas.