Chronic Pain Relief
In surgical practice, the patient with chronic pain may present for treatment of the cause (e.g. pancreatitis) or have concomitant pathology. Surgery itself may have been the cause of the now chronic symptom, as acute pain may progress to chronic pain. There is a developing belief that inadequate treatment of acute pain may make this more likely.
Chronic, intractable pain may be of malignant or benign origin and of several types.
• Nociceptive pain — pain may result from musculoskeletal disorders or cancer activating cutaneous nociceptors. Prolonged ischaemic or inflammatory processes results in sensitisation of peripheral nociceptors and altered activity in the central nervous system leading to exaggerated responses in the dorsal horn of the spinal cord. The widened area of hyperalgesia and increased sensitivity (allodynia) has been attributed to increased transmission of afferent pain impulses consequent upon this spinal cord dynamic plasticity.
• Neuropathic (or neurogenic) pain — dysfunction in peripheral or central nerves (excluding the physiological pain due to noxious stimulation of the nerve terminals). Neuropathic pain is classically ‘burning’, ‘shooting’ or ‘stabbing’, and may be associated with allodynia, numbness and diminished thermal sensation. It is poorly responsive to opioids. Examples include trigeminal neuralgia, metatarsalgia, postherpetic and diabetic neuropathy. Monoaminergic, tricyclic and anticonvulsant drugs are the mainstay of treatment.
• Psychogenic pain — psychological factors play a greater or lesser role in many chronic pain syndromes. Whichever the primary cause may have been, depressive illness and chronic pain may exacerbate each other.
The treatment of pain of malignant origin differs from that of pain of a benign cause, and may be the more difficult to overcome. Drugs, preferably, should be taken by mouth, but the patient must be regularly reassessed to ensure that analgesia remains adequate as the disease process changes.
In intractable pain, the underlying principle of treatment is to encourage independence of the patient and an active life in spite of the symptoms. The main guide to the management of cancer pain is the World Health Organisation Booklet (now in
its second edition), which portrays three levels of treatment. The ‘pain stepladder’ includes the following treatments:
• first rung: simple analgesics — aspirin, paracetamol, NSAIDs, tricyclic drugs or anticonvulsant drugs;
• second rung: intermediate strength opioids — codeine, tramadol or dextropropoxyphene;
• third rung: strong opioids — morphine. (Pethidine has been withdrawn from the second edition.)
Oral opiate analgesia is necessary when the less powerful analgesic agents no longer control pain on movement, or enable the patient to sleep. Fear that the patient may develop an addiction to opiates is usually not justified in malignant disease.
Oral morphine can be prescribed in shortacting liquid or tablet form and should be administered regularly every 4 hours until an adequate dose of drug has been titrated to control the pain over 24 hours. Once this is established, the daily dose can be divided into two separate administrations of enteric-coated, slow-release morphine tablets (MST morphine) every 12 hours. Additional short-acting morphine can then be used to cover episodes of ‘breakthrough pain’. Nausea is a problem early in the use of morphine treatment and may need control by antiemetic agents, e.g. haloperidol, methotrimeprazine, metoclopramide or ondansetron. Nausea does not usually persist, but constipation is frequently a persistent complication requiring regular prevention by laxatives.
In fusion of subcutaneous, intravenous, intrathecal or epidural opiate drugs
The infusion of opiate is necessary if a patient is unable to take oral drugs. Subcutaneous infusion of diamorphine is simple and effective to administer. Epidural infusions of diamorphine can be used on mobile patients with an external pump. Intrathecal infusions are prone to infection, but implantable reservoirs with pumps programmed by external computer are being used for long-term intrathecal analgesia. Intravenous narcotic agents may then be reserved for acute crises, such as pathological fractures.
Neurolytic techniques in cancer pain
These should only be used if the life expectancy is limited and the diagnosis is certain. The useful procedures are:
• subcostal phenol injection for a rib metastasis;
• coeliac plexus neurolytic block with alcohol for pain of pancreatic, gastric or hepatic cancer. Image intensifier control is essential;
• intrathecal neurolytic injection of hyperbaric phenol — this technique is useful only if facilities for percutaneous cordotomy are not available as it can damage motor pathways;
• percutaneous anterolateral cordotomy divides the spinothalamic ascending pain pathway — this is a highly effective technique in experienced hands, selectively eliminating pain and temperature sensation in a specific limited area.
Alternative strategies include:
• the development of hormone analogues, such as tamoxifen and cyproterone, enables effective pharmacological therapy for the pain of widespread metastases instead of pituitary ablation surgery;
• palliative radiotherapy can be most beneficial for the relief of pain in metastatic disease;
• adjuvant drugs such as corticosteroids to reduce cerebral oedema or inflammation around a tumour may be useful in symptom control. Tricyclic antidepressants, anticonvulsants and, occasionally, flecainide are also used to reduce the pain of nerve injury.
Pain control in benign disease
Surgical patients may have persistent pain from a variety of disorders including chronic inflammatory disease, recurrent infection, degenerative bone or joint disease, nerve injury and sympathetic dystrophy. Chronic pain may result from persistent excitation of the nociceptive pathways in the central nervous system, invoking mechanisms such as spontaneous firing of pain signals at N-methyl-o-aspartate receptors in the ascending pathways. Such activity is poorly responsive to opiates; neuroablative surgery is unlikely to produce prolonged benefit and may make the pain worse.
As is well known, amputation of limbs may result in phantom limb pain, the likelihood being further increased if the limb was painful before surgery. Continuous regional local anaesthetic blockade (epidural or brachial plexus), established before operation and continued postoperatively for a few days, is believed to reduce effectively the establishment of phantom pain.
The following are treatments for chronic pain of benign origin.
• Local anaesthetic and steroid injections — these can be effective around an inflamed nerve and they reduce the cycle of constant pain transmission with consequent muscle spasm. Epidural injections are used for the pain of nerve root irritation associated with minor disc prolapse. This treatment should be in association with active physiotherapy to promote mobility.
• Nerve stimulation procedures — acupuncture, transcutaneous nerve stimulation and the neurosurgical implantation of dorsal column electrodes aim to increase the endorphin production in the central nervous system altering pain transmission.
• Nerve decompression — decompression of the trigeminal nerve at craniotomy is now performed for trigeminal neuralgia, rather than percutaneous coagulation of the trigeminal ganglion, in patients who are fit for craniotomy.
Treatment of pain is dependent on sympathetic nervous system activity. Even minor trauma and surgery (often of a limb) can provoke chronic burning pain, allodynia, trophic changes and resultant disuse. The syndrome has been attributed to excessive sympathetic adrenergic activity inducing vasconstriction and abnormal nociceptive transmission. Management may include:
• test response to systemic alpha-adrenergic blockade using intravenous phentolamine;
• intravenous regional sympathetic blockade using guanethidine, under tourniquet;
• local anaesthetic injection of stellate ganglion or lumbar sympathetic chain.
Percutaneous chemical lumbar sympathectomy with phenol under radiographic control is practised by both surgeons and anaesthetists for relief of rest pain in advanced ischaemic disease of the legs. It can also promote the healing of ischaemic ulcers by improving peripheral blood flow.
Drugs in chronic benign pain
Escalating doses of opioid analgesic drugs are to be avoided, and certainly the patient must not become dependent on analgesic injections. However, for debilitating levels of chronic pain, opioid drugs are indicated. Combinations of drugs often prove useful to achieve the optimal combination of efficacy with minimal side-effects.
Paracetamol and NSAIDs are the mainstay of musculoskeletal pain treatment, but NSAIDs are handicapped by gastrointestinal intolerance and peptic ulceration. These carry significant levels of noncompliance, contraindication and morbidity. Specific cyclo oxygenase 2 inhibition, with preservation of protective cyclo-oxygenase 1 activity, promises to improve tolerability and safety in nonsteroidal anti-inflammatory treatment.
The tricyclic antidepressant drugs and anticonvulsant agents are often useful for diminishing the pain of nerve injury, although side-effects can prove troublesome and reduce compliance.
In the management of chronic pain of benign cause, a multidisciplinary approach by a team using psychologists, physiotherapists and occupational therapists under medical supervision can often achieve much more benefit than the use of powerful drugs. To help the chronic benign pain patients who do not respond to conventional means, ‘pain management programmes’ have been devised, comprising a multidisciplinary approach of pain specialists, psychologists, physiotherapists and occupational therapists. They help a number of the patients to cope with the pain and resume a higher quality life.
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