Assessment and measurement of pain

November 9, 2012 | By | Reply More

Assessment and measurement of pain

Accurate assessment of the patient is the first step in providing good analgesia.
History and measurement of pain  
A history of the patient’s general health status should be taken with a full pain history, to establish its causes and underlying diagnoses. Patients may have more than one pain, e.g. bone and neuropathic pain from skeletal metastases . A diagram of the body on which the patient can mark the pain site can be helpful. If patients are asked to score pain, they consistently rate it higher than their physicians and nurses, and patient-rated pain measurement is therefore an essential part of overall assessment and assessment of the effect of treatment. Methods include:
verbal rating scale: different verbal descriptions used to rate pain-‘no pain’, ‘mild pain’, ‘moderate pain’ and ‘severe pain’ 11 point scale: a question such as ‘Over the past 24 hours, how would you rate your pain if 0 is no pain and 10 is the worst pain you could imagine?’

Psychological aspects of chronic pain  
Perception of pain is influenced by many factors other than the painful stimulus, and pain cannot therefore be easily classified as wholly physical or psychogenic in any individual . Patients who suffer chronic pain will be affected emotionally, and conversely emotional stress can exacerbate physical pain . Full assessment for symptoms of anxiety and depression is fundamental to effective pain management.
This should include careful assessment of the painful area, looking for signs of neuropathic pain or bony tenderness, suggestive of bone metastases. In patients with cancer, do not assume that all pains are due to the cancer or its metastases.
Appropriate investigations  
Investigations should be directed towards diagnosis of an underlying cause, remembering possible reversible causes even in patients with terminal cancer. Imaging may be indicated, such as plain X-ray for fracture or MRI for spinal cord compression.

Many of the principles of pain management apply to any painful condition. However, some interventions, such as strong opioids, either have, or are perceived to have, a greater chance of harm in patients with a good prognosis. Acute pain post-surgery or following trauma should be controlled with medication without causing unnecessary side-effects or risk to the patient. Chronic, non-malignant pain is more difficult. It may be impossible to relieve pain completely and there is a greater emphasis on non-pharmacological treatments and enabling the patient to cope with pain.

The WHO analgesic ladder
The basic principle of the WHO ladder  is that analgesia should be prescribed which is appropriate for the degree of pain and increased until the pain is controlled. If pain is severe or remains poorly controlled, strong opioids should be prescribed.
Generally, a patient with mild pain is started on a non-opioid analgesic drug, e.g. paracetamol 1 g 6-hourly (step 1). If the maximum recommended dose is not sufficient or the patient has moderate pain, a weak opioid, e.g. codeine 60 mg 6-hourly, is added (step 2). If adequate pain relief is still not achieved with the maximum recommended dosages or if the patient has severe pain, a strong opioid is substituted for the weak opioid (step 3). It is important not to move ‘sideways’ (change from one drug to another of equal potency) on a particular step of the ladder. All patients with severe pain should receive a full trial of strong opioids with appropriate adjuvant analgesia, as described below.
This is effective when taken alone or in combination with opioids for mild to moderate pain. For severe pain it is inadequate alone, but remains a useful and well-tolerated adjunct.
Non-steroidal anti-inflammatory drugs (NSAIDs)  
These are effective in the treatment of mild to moderate pain, and are also useful adjuncts in the treatment of severe pain. Adverse effects  may be serious, especially in the elderly.
Weak opioids  
Codeine and dihydrocodeine are weak opioids. They have lower analgesic efficacy than strong opioids and a ceiling dose. They are effective for mild to moderate pain.

Strong opioids  
Immediate-release (IR) oral morphine takes about 20 minutes to take effect and usually provides pain relief for 4 hours. Most patients with continuous pain should initially be prescribed IR oral morphine every 4 hours (i.e. six times daily), which will provide continuing pain relief over the whole 24-hour period. Controlled-release (CR) morphine lasts for 12 or 24 hours but takes much longer to take effect. It should only be used once the correct dose has been found by a process of dose titration with IR morphine until adequate pain relief is achieved.
In addition to the regular dose, an extra dose of IR morphine should be prescribed ‘as required’ for when the patient has any pain not controlled by the regular prescription (‘breakthrough’ pain). The dose should be the same as the regular 4-hourly dose. The frequency of breakthrough doses should be dictated by their efficacy and any side-effects, rather than by a fixed time interval. A patient may require hourly doses if pain is severe, but this should lead to early review. The patient and/or carer should note the timing of any breakthrough doses and the reason for them. This should be reviewed daily and the regular 4-hourly dose increased for the next 24 hours on the basis of:
frequency of and reasons for breakthrough analgesia
degree and acceptability of side-effects.

The regular 24-hour dose should then be increased by the sum of the breakthrough doses over the previous 24 hours, unless there are significant problems with unacceptable side-effects. When the correct dose has been established, a CR preparation can be prescribed, usually twice daily.
Worldwide, the most effective and appropriate route of administration is oral, though transdermal preparations of strong opioids (usually fentanyl) are extremely useful in certain situations (e.g. patients with dysphagia, or reluctant to take regular tablets). Diamorphine is a highly soluble strong opioid used for subcutaneous infusions, particularly in the last few days of life, but is only available in certain countries.
Nausea and vomiting occur initially but usually settle after a few days. Opioids can cause confusion and drowsiness which are dose-related and reversible. In acute dosing, respiratory depression can occur but this is rare in a patient on regular opioids.
Opioid toxicity  
All patients will develop dose-related side-effects such as nausea, drowsiness, confusion or myoclonus at some point; the dose at which this occurs varies from 10 to 5000 mg of morphine depending on the patient and the type of pain. This is termed morphine toxicity and is managed by reducing the dose and returning to IR morphine so that dose adjustments can be made more rapidly. Parenteral rehydration may be necessary and the pain should be reassessed to ensure appropriate adjuvants are being used. Switching to an alternative strong opioid may be helpful.

Side-effect Management
Constipation Regular laxative, e.g. co-danthramer or co-danthrusate (starting dose 2 capsules o.d.; titrate laxative)
Dry mouth Frequent sips of iced water, soft white paraffin to lips, chlorhexidine mouthwashes 12-hourly, sugar-free gum, water or saliva sprays
Nausea/vomiting Haloperidol 1.5-3 mg nocte or metoclopramide/domperidone 10 mg 8-hourly
In cases of constant nausea a parenteral antiemetic is necessary to break the nausea cycle
Sedation Explanation very important
Expect to settle in about 2-3 days
Avoid other sedating medication where possible
Ensure appropriate use of adjuvant analgesics which can have an opioid-sparing effect

Alternatives to morphine include oxycodone, transdermal fentanyl, hydromorphone and occasionally methadone, which may produce a better balance of benefit against side-effects. Oxycodone and fentanyl have no renally excreted active metabolites and may be particularly useful in patients with renal failure. Pethidine is used in acute pain management but should not be used to manage chronic pain because of its short half-life and ceiling dose.
Adjuvant analgesics  

An adjuvant analgesic is a drug with a primary indication other than pain but which is analgesic in some painful conditions and may enhance the effect of primary analgesia. At each step of the WHO analgesic ladder, an adjuvant analgesic should be considered, the choice depending on the type of pain.

Drug Dosage Indications Side-effects*
NSAIDs e.g. diclofenac 50 mg oral 8-hourly (SR 75 mg 12-hourly) 100 mg per rectum once a day Bone metastases, soft tissue infiltration, liver pain, inflammatory pain Gastric irritation and bleeding, fluid retention, headache; caution in renal impairment
Corticosteroids e.g. dexamethasone 8-16 mg per day; use morning (titrate down to lowest dose which controls pain) Raised intracranial pressure, nerve compression, soft tissue infiltration, liver pain Gastric irritation if used together with NSAID, fluid retention, confusion, Cushingoid appearance, candidiasis, hyperglycaemia
Gabapentin 100-300 mg nocte (starting dose) (titrate to 600 mg 8-hourly) Neuropathic pain of any aetiology Mild sedation, tremor, confusion
Carbamazepine (evidence for all anticonvulsants) 100-200 mg nocte (starting dose) Neuropathic pain of any aetiology Vertigo, sedation, constipation, rash
Amitriptyline (evidence for all tricyclics) 25 mg nocte (starting dose) 10 mg (elderly) Neuropathic pain of any aetiology Sedation, dizziness, confusion, dry mouth, constipation, urinary retention; avoid in cardiac disease

Radiotherapy has a place in the management of bone metastases .
One of the key aims of pain management is to alleviate suffering and restore function, so physiotherapy and active mobilisation must be considered early. Pain may respond to spinal manipulation, massage, application of heat or cold, and exercise. Immediate cold application (e.g. ice packs) reduces subsequent swelling and inflammation after sports injury.
Psychological techniques  
Psychological techniques include simple relaxation, hypnosis, cognitive behavioural therapies and biofeedback . These train the patient in coping strategies and behavioural techniques. This is clearly more relevant in chronic non-malignant pain than in cancer pain.

Stimulation therapies  
Acupuncture has been used successfully in Eastern medicine for centuries. It causes release of endogenous analgesics (endorphins) within the spinal cord. Transcutaneous electrical nerve stimulation (TENS) may have a similar mechanism of action to acupuncture and can be used in both acute and chronic pain.
Herbal medicine and homeopathy  
These are widely used for pain, but often with little evidence for efficacy . Safety regulations for these treatments are limited compared with conventional drugs, and the doctor should be wary of unrecognised side-effects which may result.

Category: Medicine

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