Chronic post-surgical pain: prevention and management
With Dr Deepak Ravindran | 23 Feb 2015 | Print
Dr Deepak Ravindran is consultant in anesthesia and pain medicine, Royal Berkshire Hospital, Reading, UK.
In the last 10 years, there has been increasing recognition of the fact that a significant percentage of patients report chronic pain after a wide variety of surgeries. Chronic postsurgical pain (CPSP) is a major problem with societal consequences and effect on quality of life. Up to about a third of patients report persistent or intermittent pain one year after common surgical procedures. It is therefore important to identify possible risk factors, understand pathological mechanisms and establish preventive strategies.
The following criteria have been suggested to define CPSP:
- Pain that develops after a surgical procedure
- Pain lasting at least two months
- Other causes such as chronic infection have been excluded
- The possibility that the pain is continuing from a pre-existing problem has been excluded.
A survey of 5,130 patients attending outpatient pain clinics revealed that 22.5% of patients cited surgery as their main cause of chronic pain. The figure for the general population is likely to be significantly higher since not all patients come into secondary care. A more recent cross-sectional survey of 12,982 participants showed that, among respondents who had undergone surgery more than three months prior to being surveyed (n=2,043), 40.4% reported chronic pain, 18.3% reported moderate to severe pain and sensory abnormalities were reported by 24.5%.
The common surgical procedures include inguinal hernia repair and breast, orthopedic and cardiothoracic surgery. The incidence of chronic pain is 12% for patients undergoing hernia repair and is now the most common long-term problem after such surgery. Rates of CPSP are much higher after mastectomy with reconstruction (49%) compared with mastectomy alone (31%).
A number of putative risk factors have been identified that may contribute to development of CPSP (Table 1).
Genetic susceptibility is likely to play a role in the development of CPSP. For example, single nucleotide polymorphisms coding for the catechol-O-methyltransferase enzyme are associated with the development of chronic pain conditions such as temporomandibular joint disorder. Genetic variability in the expression of enzymes responsible for neurotransmitter synthesis in the dorsal root ganglion is associated with persistent pain after lumbar discectomy.
There are no studies as yet that have included all the above factors and therefore there is no clear consensus on the mechanisms involved and hence prevention and management of the problem.
Table 1. Putative risk factors for chronic postsurgical pain
Preventive strategies and treatment
A positive correlation between sensory abnormalities and pain as reportedsuggests that neuropathic mechanisms are responsible in a majority of pain cases. Once nerve injury has occurred, a wide variety of inflammatory mechanisms are activated leading to peripheral and central sensitization by release of various neuro-transmitters. Our knowledge of acute pain physiology and its transition to chronic pain would suggest that one therapeutic strategy or single modality treatment is unlikely to work once this diffuse and complex neural pathway activation occurs.
This increase in awareness of CPSP has led to a huge body of research looking into pre-emptive and preventive strategies. The challenge is to accurately identify at-risk patients and target suitable interventions.
Pre-emptive epidural analgesia (regional analgesia commenced before surgery) has not shown much benefit for preventing CPSP. A meta-analysis of pre-emptive epidural compared with epidural commenced after completion of thoracic surgery did not affect development of CPSP.
Many of the risk factors are difficult to influence or alter but there is no doubt that severity of acute postoperative pain influences CPSP. Effective treatment of acute pain after surgery can reduce the incidence of CPSP by preventing sensitization of the CNS. A combined systematic review and meta-analysis looked at the utility of using gabapentin and pregabalin in preventing CPSP.Eight trials were included in the meta-analysis and they showed that six of the gabapentin trials demonstrated moderate-to-large reduction in the development of CPSP, while two of the pregabalin trials showed a very large reduction in development of CPSP. Pre-emptive analgesia using drugs such as gabapentin or pregabalin (off-license) administered pre-operatively and continued postoperatively are now part of most procedure-specific pain management protocols in the UK, and are included in enhanced recovery pathways.
Regional blockade by itself is often insufficient and therefore a multimodal approach utilizing regional blockade (central/peripheral), NSAIDs, drugs for neuropathic pain and other analgesics including opioids is the best way forward.
A major preventive factor often less discussed is not having the surgical procedure itself. Inappropriate or unnecessary surgery needs to be prevented. Alternatives to surgery should be explored and patients must be made aware of risks so that a truly informed choice is made. Public education should be improved to both patients and their carers in order to help remove the belief that something must have gone wrong at the time of surgery.
Once CPSP has occurred it is difficult to cure, but there are a number of interventions that can be helpful in reducing pain. Initial management in primary care would include patient education, counselling and self-management followed by the use of anti-neuropathic medication such as amitriptyline, gabapentin and pregabalin. Depending on the extent and severity of the pain and its effect on quality of life, pain specialists can employ a variety of interventions such as local infiltrations of steroids[13,14] and diagnostic nerve blocks followed by neuromodulation techniques within a multidisciplinary model. Although the evidence base for these techniques is limited, when chosen appropriately, they can provide hope.
CPSP is a significant public health issue. As its development is likely to be multifactorial, large scale, multicenter randomized studies are urgently needed to aid better understanding of CPSP. Meanwhile, our aim should be to minimize unnecessary and inappropriate surgery, provide sustained and effective perioperative pain relief and detect and treat postoperative neuropathic pain in an early and aggressive manner using a multimodal strategy.
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