FRCA Notes

Chronic Post-Surgical Pain

This topic has come up as a CRQ question in both 2020 (pass rate 61%) and 2023 (66%), with surprisingly complimentary examiner feedback.

> It was also an SAQ in 2017, where the bulk of the marks were for knowing the risk factors for, and surgeries associated with, the condition.

Resources

  • Chronic post-surgical pain (CPSP) is an increasingly common phenomenon, with important healthcare and economic consequences

  • The overall median incidence of chronic post-surgical pain is quoted as 10%, but there is a wide range
    • Incidence of CPSP at 6 - 12 months post-operatively is 20 - 30%
    • This varies by type of surgery, but is more likely after hip & knee arthroplasties
  • CPSP is defined in ICD-11 as:
    • Pain which develops, or increases in intensity, after a surgical procedure or tissue injury
    • Persisting beyond the healing process (>3 months after the triggering event)
    • Localised to the surgical area or a related innervation territory (i.e. an area projected onto the innervation of a nerve involved the surgical area or a dermatome or Head's zone)

  • Also requires:
    • Other causes of pain to be excluded
    • Caused by tissue trauma which arises from a surgical procedure (as opposed to uncontrolled/accidental damage e.g. trauma)

  • The aetiology of CPSP is polyfactorial; there are patient, pain and surgical risk factors that increase risk of CPSP

Patient factors

  • Younger age
  • Female gender
  • Smoker
  • Raised BMI
  • Low education level
  • Low socio-economic status
  • Previous addiction or disability
  • Psychological factors including anxiety, depression, pain catastrophising

Surgical factors

  • Other surgeries at higher risk are those which are:
    • More traumatic (i.e. open vs. endoscopic)
    • Of longer duration
    • A repeat/re-do surgery
    • Responsible for intra-operative nerve injury
    • Beset by post-operative complications (BJA, 2022)

Pain-related factors

  • An increased severity/intensity of pre-operative pain
    • Includes chronic use of opioids
    • Includes chronic pain conditions such as fibromyalgia, migraine or chronic back pain

  • Acute post-operative pain of increased intensity and/or duration, particularly if it is visceral or neuropathic in nature

Prediction

  • One predictive model (BJA, 2022) found CPSP can be fairly reliably predicted by the combination of:
    • Requirement for pe-operative opioid treatment
    • Bone surgery
    • The pain score at day 14 post-operatively
    • The presence of painful cold sensation at the surgical site at day 14 post-operatively

  • The mechanism is complex, involving both peripheral sensitisation at the site of injury and central sensitisation in spinal and supra-spinal levels
  • The inflammatory and immune responses to tissue/axonal injury lead to:
    • Microglial activation
    • Ectopic neural activity
    • Altered dorsal horn activity
    • Changes in supraspinal processing, including changes in endogenous descending pain modulation
  • Other mechanisms may play a greater role in procedures less likely to be associated with neuropathic CPSP

  • Pain can be neuropathic, nociceptive or a mixture
  • The central sensitisation in CPSP leads to typical neuropathic symptoms in 35 - 57% of patients, such as:
    • Allodynia
    • Hyperalgesia (whose presence may be predictive of a prolonged neuropathic pain)
    • Dysaesthesia

  • Although the incidence of neuropathic pain varies by surgery, it is commonest after:
    • Thoracotomy - subcostal nerve damage
    • Mastectomy - brachial plexus or axillary nerve injury
    • Amputation

Prevention

  • Attempts at predicting and preventing CPSP are generally beset by a lack of validated systems & absence of robust evidence for preventative strategies
  • Understanding those at highest risk (see above) and modifying the modifiable will help
  • Naturally, a multi-modal analgesic regimen and biopsychosocial approach to pain will be of benefit in reducing the incidence of CPSP

Non-pharmacological

  • Speaking of biopsychosocial, an MDT approach with physiotherapy, psychotherapy and patient education will be fruitful
  • Evidence suggests use of transitional pain services reduces long-term analgesic and opioid use (BJA, 2021)

Pharmacological

  • The most effective agents for reducing the incidence and severity of CPSP at six months (BJA, 2023) are:
    1. Ketamine - may be particularly beneficial for patients on pre-operative, long-term opioids
    2. IV lidocaine
    3. Gabapentinoids
      • Gabapentinoids have not been shown to reduce incidence of CPSP when used preoperatively
      • They may, however help manage neuropathic pain and are therefore appropriate treatments for CPSP
    4. Dexmedetomidine

  • Others
    • Duloxetine: may reduce post-operative pain 12 weeks after surgery
    • Inadequate literature to comment on clonidine or nefopam