The Influence of the Pre-operative Nociceptive Profile on the Development of 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) 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 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 will have a lower risk to develop
chronic pain after surgery compared to patients with a pro-nociceptive profile.
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.

This is a two-site, observational study. Patients will be operated by surgeons
from the Leiden University Medical Center (LUMC) in Leiden or the Reinier de
Graaf Groep (RdGG) in Delft.

In all patients the effectiveness of the endogenous analgesia system will be
assessed 0-14 days before the surgery. An experienced experimenter will conduct
the psychophysical assessment. The endogenous analgesia system will be
evaluated using 2 separate psychophysical tests: 1) conditioned pain
modulation, and 2) temporal summation. Both heat stimuli and electrical stimuli
will be used. After surgery, we will record acute pain intensity and analgesic
consumption during the first 24 hours. A monthly phone call for chronic
post-operative pain and analgesic use will be pursued for 6 months. One year
after surgery there will be a last assessment of pain (via telephone). For
patients without chronic pain this is the study end. When patients do present
them selves with chronic pain one year after surgery, we will invite these
patients back in to the RdGG for one final assesment of the endogenous
analgesia system.

The pain test may give redness and a burning sensation of the skin in the first
24 hours after the testing.