Postoperative Analgesia and Antihyperalgesia of Tramadol and Acetaminophen Per Oral After Caesarean Section -A Randomised Controlled Trial in Female O-Desmethyl 1 Metabolizers Identified by the Respective Gene-

Caesarean section rate is growing in western countries (from 9% by 1980, to 12% by 1990 up to 22-24% in 2002)1.

Pain after Caesarean section involves 2 components, somatic pain from the wound and visceral pain from uterine contractions2. Different mechanisms underlie somatic and visceral pain transmission, at spinal and supraspinal levels, supporting different sensitivity to analgetics2. Pain at rest is usually well controlled by parenteral opioids, while pain induced by movements is less responsive to opioids, requesting higher doses with an increase of side effects3.

Beyond the concern of short term recovery, postoperative pain management has an impact on the risk of developing residual pain after surgery4. Following Caesarean section 18% of patients still suffer from pain 3 months after surgery. 12% still complain after 10 months and for 6% pain is a significant problem, interfering with quality of life and being present daily or almost daily5.

Central sensitization, clinically expressed as hyperalgesia and allodynia, not only contributes to postoperative pain perception, but also is associated with the presence of chronic pain state6.

Aside from tissue damage, the most striking risk factor for developing residual pain seems to be the level of immediate postoperative pain7.