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.
Malignant
disease
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:
• 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.