Case of the Month #45: Chronic Pain After Hernia Surgery
Discussion
What is Chronic post-surgical pain?
Chronic post-surgical pain (CPSP) is defined as chronic pain that develops after a surgical procedure and persists even after the time period of the healing process is complete i.e 3 months. The pain is either localized to the surgical field or present in the area of innervation territory of the nerve situated in the area of surgery or referred to the dermatome of the supply of that nerve1. It is characterised as burning, stabbing or shooting pain, numbness or change to sensation (allodynia) and exaggerated response (hyperalgesia) when it is predominantly neuropathic. It can also be nociceptive due to inflammation and tissue damage. It can be mixed pain with the characteristics of both nociceptive and neuropathic pain present.
- What is the mechanism?
Peripheral and central sensitization is key. Inflammation and an immune response to tissue and nerve damage results in release of neurotransmitters peripherally and centrally leading to microglial activation, ectopic neural activity and altered activity in the dorsal horn leading to allodynia and hyperalgesia2.
The amount of tissue damage, nerve damage and inflammation from operative and postoperative changes may influence chronic postoperative pain development, but patient characteristics have been proven to correspond to different degrees of this.
- What are the risk factors?
Patient related risk factors include:
Young (adult) age; female sex; BMI; education status and socioeconomic factors; poorly controlled acute postoperative pain; preexisting pain; long term opioid use, and psychological risk factors, such as psychological distress, anxiety, catastrophizing, reduced ability to cope with pain, depression and hypervigilance.
A recent meta-analysis highlights anxiety as the main psychological risk factor and to a lesser degree, depression, catastrophizing, kinesiophobia and impaired self-efficacy3•
Genetic variations include several single nucleotide polymorphisms within three genes involved in dopamine neurotransmission (catechol-O-methyltransferase (COMT), GTP cyclohydrolase 1(GCH1) and DA receptor 2 (DRD2) ) seem to be related to the risk of developing chronic postoperative pain4.
- Surgery related risk factors
Although the extent of the surgical trauma and duration of surgery are predictive factors, the type of tissue injured is also relevant. This could explain why minimally invasive surgery does not always reduce the risk1. For example a laparoscopic approach can reduce the risk in certain types of surgery, such as hernia repair and cholecystectomy, but not after gastrointestinal surgery and nephrectomy.
Postoperative complications, reoperation, infection or adjuvant therapies, such as radio- or chemotherapy, are additional risk factors.
- Operations with a high risk of developing CPSP:
Inguinal hernia repair
Mastectomy
Amputations
Thoracotomy
Sternotomy
Knee replacement
Postoperative wound infection can delay the healing process as well as cause scarring, potentially resulting in nerve damage, which may increase the risk5.
Multimodal analgesia with perioperative regional anaesthesia has been shown to reduce the risk of CPSP in most types of surgery studied so far. By blocking nociceptive input to the central nervous system, central sensitisation processes can be reduced if not prevented2.
A multidisciplinary approach, including physiotherapy and psychological specialist input would be recommended for patients who suffer with complex persistent pain conditions6.