4.1 Persistent Post Surgical Pain

Question 1

a) Define persistent postoperative pain.

Answer 1

Persistent postoperative pain is defined as pain having the following features:

● Pain that develops after a surgical procedure.

● Pain that is persistent for more than
2 months following a surgical procedure
.
● Other causes for this pain have been excluded
(e.g. infection, malignancy, etc).

● The possibility that pain is due to a
pre-existing cause has been excluded.

Question 2

b) List five surgical procedures that are most commonly
associated with persistent postoperative pain.

Answer 2

● Amputation.

● Thoracotomy.

● Cardiac surgery.

● Mastectomy.

● Breast augmentation.

● Iliac crease bone harvest site.

● Knee arthroplasty.

● Radical prostatectomy.

● Hernia repair.

● Caesarean section.

● Hip replacement.

Question 3

c) What are the risk factors for the development of persistent
postoperative pain?

Answer 3

The risk factors are multifactorial.
Patient factors:
● Psychological factors such as catastrophisation,
anxiety and depression can increase the risk.

● Preoperative pain in the operative area
increases the risk of persistent postoperative pain.

● Inadequate and interrupted sleep increases the risk.

● Genetic differences/polymorphisms in pain processing, causing an altered sensitivity to pain,
differences in opioid receptors and
variations in metabolism of analgesics.

● Good descending noxious inhibitory control
reduces the risk of persistent postoperative pain.

● The first 7 days median pain scores after
a surgery are more predictive
of persistent postoperative pain.

● Poor pain control with medications during the first week
postoperatively due to factors like improper instructions to the
patients for analgesia, patients fearing addiction to drugs such as
opioids or patients experiencing analgesic-related adverse effects.

● Younger patients tend to have more
persistent postoperative pain.
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Surgical factors:
● There is more chronic persistent pain with open surgery compared with laparoscopic surgery.

● Postoperative complications such as
reoperation, infection, wound dehiscence, haematoma.

● Intraoperative non-identification of nerves causing
damage due to diathermy or entrapment.
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Anaesthetic factors:
● Regional anaesthesia including epidural anaesthesia
(after amputations, thoracotomies, major intra-abdominal surgeries)

or

paravertebral blocks (for mastectomies) may be beneficial for
reducing the incidence of persistent postoperative pain.

● Severe persistent acute post-surgical pain.

● The use of adjuvants in regional blocks, e.g. clonidine.

Question 4

d) What pathophysiological changes occur at the spinal cord level during the transition from acute to persistent postoperative
pain?

Answer 4

● Central sensitisation —
repetitive nociceptive stimuli,
altered dorsal horn activity and
amplification of sensory flow.

● Immune-mediated inflammatory reactions,
hypersensitivity and ectopic neural activity.

● Expansion of receptive fields of central neurones.

● Reduced thresholds for responses at the spinal cord level.

● Activation of spinal cord microglial cells occurs
which modulates the synaptic function.

● Altered expressions of Na+ channels.