Management of Chronic Pain
Recent advances in the understanding of the fundamental mechanisms involved in the transmission and modulation of noxious impulses have significantly extended the range of assessment tools and treatments clinicians offer to patients with pain. The majority of medical pain specialists in the UK are anaesthetists. Historically, anaesthetists have been responsible for the relief of pain in the perioperative period and have developed skills in percutaneous neural blockade. This expertise, developed originally with local anaesthetics, was then extended to neurolytic agents. Initially, pain clinics started as nerve-blocking clinics and most pain management clinics continue to be directed by anaesthetists who now have access to a formal training programme supervised by the Faculty of Pain Medicine of the Royal College of Anaesthetists, and specialist recognition. However, with increasing awareness of the complexity of the pain experience, there has been recognition that other healthcare professionals have a significant role in the management of patients with chronic pain. A multidisciplinary approach involving anaesthetists, other healthcare professionals, such as psychologists, physiotherapists, occupational therapists, nurse specialists, and other medical practitioners, is the preferred management model for people with pain. Evidence-based practice is now firmly established in clinical decision-making, particularly in formulating guidelines and consensus documents. Pain management clinics are available in most hospitals in the United Kingdom, with local variation in the services offered. Some offer specialist clinics for specific conditions (e.g. pelvic pain clinic, paediatric pain clinic) or treatments (e.g. spinal cord stimulators).
Current health trends are supporting the delivery of pain management services in primary care and in the community, because many patients can be managed in a primary care setting without needing to be referred to hospital. There is an increasing trend to involve the patient as an active participant of treatment and to include self-management strategies as part of the management plan.
Pain: ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’ (The International Association for the Study of Pain, http://www.iasp-pain.org/AM/Template.cfm?Section=Pain_Definitions). This definition emphasizes that pain is not only a physical sensation but also a subjective psychological event. It accepts that pain may occur in spite of negative physical findings and investigations. Pain has sensory, cognitive and motivational-affective dimensions and has been described as a biopsychosocial experience, as illustrated in Figure 46.1. This must be taken into account when assessing and planning a treatment strategy for the patient with pain.
Chronic pain syndrome can adversely affect the patient in various ways, including depressed mood, fatigue, reduced activity and libido, excessive use of drugs and alcohol, dependent behaviour and disability out of proportion to impairment. It does not respond to the medical model of care and is best managed with a multidisciplinary approach.
Pain management concerns postoperative, acute and chronic pain and cancer-related symptom control in children and adults. A joint report of the College of Anaesthetists and the Royal College of Surgeons of England highlighted the need to improve standards of postoperative pain management and many hospitals have established acute pain teams. However, many hospitalized patients suffer from acute non-postoperative pain. This may be caused by trauma, burns or acutely painful medical conditions (e.g. cardiac pain, osteoporotic vertebral collapse). Some medical conditions may cause recurrent acute painful episodes such as sickle-cell crisis or acute exacerbations of chronic pancreatitis. Unrelieved acute pain may lead to chronic pain. Chronic pain is a complex biopsychosocial phenomenon and a single pathophysiological explanation is not available for many chronic nonmalignant pain states. Palliative care services may refer cancer-related pain problems to the anaesthetist for management as a hospital inpatient, an outpatient, in a hospice or in the home. There are many common areas within the management of acute and chronic pain, and pain is increasingly viewed as a continuum rather than two separate entities, with subsequent merging of management techniques and staff.
Postoperative, acute, recurrent, persistent and cancer-related pain occurs in children. Difficulties in pain assessment and unsubstantiated fears and myths regarding pain and its treatment in children have led to suboptimal management. Recommendations for the management of pain in children have been published.
The prevalence of chronic pain within the general population has proved difficult to estimate because of variations in the populations studied, the methods used to collect data and the criteria used to define chronic pain. Recent data have suggested that the prevalence of chronic pain in the UK is 13%, i.e. about 1 in 7 of the population. Chronic pain is the presenting complaint in 22% of primary care consultations and is estimated to account for 4.6 million GP visits per year. Patients with persistent pain consult their GPs five times more frequently than those without.
Untreated pain may reduce quality of life for sufferers and carers, resulting in helplessness, isolation, depression and family breakdown. Many patients with persistent pain have significant functional, social and financial consequences. Forty-nine percent take time off from work, 25% lose their jobs, 22% develop depression, 44% have their concentration affected and 56% have disturbed sleep.
Pain is the second commonest cause of days off work through sickness, accounting for 206 million working days lost in the UK in 1999–2000. It is the second commonest reason for people to be given Incapacity Benefit and £3.8 billion is spent per year on Incapacity Benefit for those in pain. The cost of back pain was £12.3 billion (22% of UK health expenditure) – mainly due to work days lost.
Somatic pain results from activation of nociceptors in cutaneous and deep tissues, such as skin, muscle and subcutaneous soft tissue. Typically, it is well localized and described as aching, throbbing or gnawing. Somatic pain is usually sensitive to opioids.
Visceral pain arises from internal organs. It is characteristically vague in distribution and quality and is often described as deep, dull or dragging. It may be associated with nausea, vomiting and alterations in blood pressure and heart rate. Stimuli such as crushing or burning, which are painful in somatic structures, often evoke no pain in visceral organs. Mechanisms of visceral pain include abnormal distension or contraction of smooth muscle, stretching of the capsule of solid organs, hypoxaemia or necrosis and irritation by algesic substances. Visceral pain is often referred to cutaneous sites distant from the visceral lesion. One example of this is shoulder pain resulting from diaphragmatic irritation.
Visceral hyperalgesia: increased sensitivity in the painful organ. Pain threshold is lowered in some patients with functional gastrointestinal disease and patients complain of abdominal pain in response to normally innocuous stimuli of the gut.
Referred hyperalgesia from viscera, in which hypersensitivity is localized in the muscles and often associated with a state of sustained contraction. For example, patients with urinary colic typically display hypersensitivity in the muscles of the lumbar region.
Viscero-visceral hyperalgesia: pain in one visceral organ can be enhanced by pain in another visceral organ. Women with repeated urinary stones who were also dysmenorrhoeic manifested a higher number of colics than non-dysmenorrhoeic women.
Neuropathic pain is now defined as ‘pain arising as a direct consequence of a lesion or disease affecting the somatosensory system’. It is characteristically dysaesthetic in nature and patients complain of unpleasant abnormal sensations. There may be marked allodynia, i.e. a normally nonpainful stimulus, such as light touch, evokes pain. Pain may be described as shooting or burning and may occur in areas of numbness. Neuropathic pain may develop immediately after nerve injury or after a variable interval. It is often persistent and can be relatively resistant to opioids. There is a tendency for a favourable response to centrally modulating medication, such as anticonvulsants and tricyclic and serotonin- noradrenaline reuptake inhibitor (SNRI) antidepressants.
There are many causes of neuropathic pain. Lesions in the peripheral nervous system include peripheral nerve injuries, peripheral neuropathies, HIV infection, some drugs and tumour infiltration. Central neuropathic pain is associated with lesions of the central nervous system, such as infarction, trauma and demyelination and is very resistant to treatment.
Pain which is maintained by sympathetic efferent innervation or by circulating catecholamines is termed sympathetically maintained pain (SMP) and considered a form of neuropathic pain. It may be a feature of several pain disorders and is not an essential component of any one condition. Sympathetic nerve blocks provide at least temporary reduction of pain, but current thinking is that this does not imply a mechanism for the pain. It is classified into type I (reflex sympathetic dystrophy) and type II (causalgia).
In complex regional pain syndrome (CRPS) type 1, minor injuries, including mild soft tissue trauma or a fracture, precede the onset of symptoms without any overt nerve lesion (Fig. 46.2). CRPS type II develops after injury to a peripheral nerve. Pain is the prominent feature and is characteristically spontaneous and burning in nature and associated with allodynia (abnormal sensitivity of the skin) and hyperalgesia. Autonomic changes may lead to swelling, abnormal sweating and changes in skin blood flow. Atrophy of the skin, nails and muscles can occur and localized osteoporosis may be demonstrated on X-ray or bone scan. Movement of the limb is usually restricted as a result of the pain, and contractures may result. Treatment is directed at providing adequate analgesia to encourage active physiotherapy and improvement of function. In cases with sympathetically maintained pain, sympathetic nerve block may be part of this treatment strategy.
Brachial plexus avulsion
Radicular pain of spinal origin
Chronic regional pain syndrome (CRPS)
Peripheral vascular disease
Cancer treatment-related: e.g. post-surgery, post-chemotherapy, post-radiotherapy pain
Comprehensive assessment of patients with pain is a vital first step. Pain is generally thought of as a symptom rather than a disease in its own right. Efforts should be made to investigate, diagnose and, if possible, treat the underlying cause of the pain before using empirical pain-relieving techniques. However, there is now a growing body of animal and human evidence that chronic pain may involve increased sensitivity of spinal cord neurones and changes in the spinal cord and the brain, which can be responsible for increased pain. Thus, there has been some support for persistent pain to be viewed as a condition in its own right.
The key elements of a pain history should be ascertained using a structured interview. The interview includes assessment of the pain, the effect of pain on the patient’s mood and also the impact of the pain on quality of life and functioning. Many patients with pain become physically deconditioned and their mood can deteriorate. Both factors may contribute to the pain experience. Assessment can be recorded and audited using tools such as the Brief Pain Inventory.
quality, to determine possible somatic or neuropathic aetiology, e.g. burning, shooting; validated screening tools such as The Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) pain scale can be used
basic psychological assessment to include mood, coping skills, pain beliefs and self-reported disabilities; a Hospital Anxiety and Depression (HAD) scale can assist as a screening tool but if full psychological evaluation is indicated, it should be performed either by a psychiatrist or by a clinical psychologist, preferably one who is an integral member of the pain management team
Many patients, especially the elderly and those with malignancy, have more than one site of pain and separate histories should be taken for each complaint because their aetiologies may differ. Particular care and skill are needed when taking a pain history from children and the elderly.
A physical examination relevant to the pain complaint should be performed and may include a full musculoskeletal or neurological assessment. It may involve a vaginal or rectal examination. Signs implicating involvement of the sympathetic nervous system including vasomotor, sudomotor and trophic changes should be considered. Physiotherapy assessment may be part of the initial screening interview.
Chronic pain affects not only the patient, but also the family. Some patients with chronic pain become depressed and anxious, and lose their job, and financial and social status. Their relationships may deteriorate and it may be important to interview the patient’s relatives or significant others with the patient to assess the impact of the pain on family life.