The standard treatment for post operative pain is now bupivacaine + sufentanil. The use of this combination during fast-track colonic surgery leads frequently to post-operative nausea and vomiting and limited mobilisation possibilities. Therefore the department anaesthesiology wants to evaluate the use of a different local anaesthetic: levobupivacaine combined with morphine on demand. The expectation is that the use of levobupivacaine leads to less side effects.