The influence of pre-operative pain perception on the development on chronic pain after inguinal hernia repair surgery

Postoperative pain and the development of chronic pain is a serious complication of surgical interventions. While the treatment of acute postoperative pain is well organized in current medical practice, the development of chronic pain still has a relatively large incidence. The latter depends on many factors including the type of surgery (a high incidence of postoperative chronic pain is observed following thoracotomies, mastectomies and inguinal hernia repairs) and specific patient-related factors. These patient-related factors include the state of the endogenous analgesia system, a modulatory and highly plastic system that is involved in modulation of afferent nociceptive input to central sites using top-down inhibitory and facilitatory pathways that inhibit or facilitate pain perception. The preoperative balance between anti- and pronociception may play a crucial role in the development of postoperative chronic pain. We believe that a diminished pain inhibitory system or an enhanced pain facilitatory system may enhance the risk to develop chronic postoperative pain. Some evidence for this comes from Yarnitsky et al. who showed that the ability to engage endogenous inhibitory pathways (as tested by the experimental paradigm of Conditioned Pain Modulation (CPM)) was associated with a lower risk of development of chronic post-thoractomy pain (odd ratio 0.52).1 In the current study we aim to pre-operatively test the effectiveness of the endogenous pain modulatory system (by conditioned pain modulation and temporal summation) in a large group of patients planned for an elective inguinal hernia repair.

In the current study we aim to pre-operatively test the effectiveness of the endogenous pain modulatory system. We hypothesize that patients with a pre-operative anti-nociceptive profile (measured by CPM) will have a lower risk to develop chronic pain after surgery compared to patients with a pro-nociceptive profile (measured by temporal summation). Furthermore, we will use questionnaires to evaluate the psychological state of the patients, as it is known that patients with catastrophizing, anxious or depressive thought have a higher probability to develop chronic pain. We aim to correlate psychological parameters to the chance of developing chronic pain and to treatment effects.



We hypothesize that:

1) Patients with a pro-nociceptive profile will experience more pain direct post-operative, have a higher consumption of analgesics and have a higher probability of developing chronic post-operative pain compared to patients with anti-nociceptive profile.

2) Patients with catastrophizing, anxious or depressive thoughts have a higher probability to develop chronic pain and are more likely to have a pro-nociceptive profile.

1) The effectiveness of the endogenous analgesic system as measure for the nociceptive profile, will be tested 0-14 days prior to surgery.

2) The postoperative pain scores and analgesic consumption will be measured in the recovery room.



3) The development of chronic pain will be evaluated at 1,2,3,6 and 12 months after surgery.

This study has no intervention. It is an observational study assessing the pre-operative nociceptive profile to study whether this is a predictive factor for the development of post-operative chronic pain.