Disease - Pain management

From CambridgeNotes

Pain is the 'unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.' Pain is commonly encountered in patients with advanced disease e.g. 60% of cancer patients suffer from pain.


History and Examination

Assess the cause of each of the patient's pains:

  • site, onset, characteristics, radiation, severity, exacerbating/relieving factors, timing
    • Soft tissue: localised ache, throbbing, gnawing
    • Visceral: poorly localised deep ache, referred pain
    • Neuropathic: dermatomal or radicular, dysaesthesia, associated motor/sensory loss
    • Bone: well localised ache, local tenderness
    • Incident: episodic, on movement/weight bearing/change of dressing

Treatment

1) Consider non-pharmacological measures in pain control:

  • Transcutaneous electrical nerve stimulation (TENS), acupuncture, relaxation, cognitive behavioural therapy (CBT), radiotherapy, hypnosis, surgery, nerve blocks.

2) Analgesic Drugs:

  • The choice of drugs should be based on the severity of pain not the stage of the disease.
  • The WHO analgesic ladder was developed for cancer pain management, however this simple stepwise approach using a limited number of drugs can be used for any chronic pain.
  • Move up the ladder if pain persists/worsens to titrate analgesia in order to control the pain
  • Step 1: Mild Pain: Non-opioid
    • Paracetamol: 1g qds PO/PR prn (dose limited by hepatotoxicity)
    • NSAIDS e.g. ibuprofen, diclofenac (side effects: GI ulcers/bleed, renal impairment)
      • Inhibit PGE2 synthesis thus reducing stimulation of nociceptors
  • Step 2: Moderate Pain: Non-opioid + Weak opioid
    • Codeine: 30-60mg up to qds PO/IM
      • Inhibits opioid receptors in brainstem, spinal cord and peripheral nerves, so reducing transmission of nociceptive stimuli to the brain.
      • Combination formulations:
        • Co-codamol = codeine + paracetamol
        • Co-dydramol = dihydrocodeine + paracetamol
    • Dextropropoxyphene: milder than codeine
      • Combined with paracetamol in co-proxamol
  • Step 3: Severe Pain: Non-opioid + Strong opioid
    • Morphine is the most commonly used strong opioid
    • Start with a quick release oral formulation for dose titration: oramorph, sevredol
      • 5-10mg PO every 4 hours, allowing extra doses for 'breakthrough pain' prn
      • Assess the daily requirements after 24-48 hours and adjust the regular daily dose appropriately, until pain relief is adequate (e.g. PCA)
        • The regular dose may range from 5mg to 2500mg, most require less than 200mg per day
    • Once a stable satisfactory daily dose has been found, maintenance of pain relief is achieved using controlled release morphine preparations (MST continus) od/bd
    • All patients on long-acting opioid preparations require immediate-release, short acting opioid for effective analgesia during episodes of break-through pain e.g. morphine PO 1/6th daily dose
    • Alternative routes for morphine:
      • Rectal suppositories: same dose as oral
      • Subcutaneous infusion via portable syringe driver: halve the oral dose as more potent via subcutaneous route (higher bio-availability)
      • Intravenous: e.g. via indwelling central line
    • Common adverse effects of opioids:
      • Sedation: especially when commencing therapy
      • Nausea and vomiting: usually resolves after a few days but can be controlled by metoclopramide (10mg PO tds) or haloperidol (1.5mg PO tds)
      • Constipation: develops in almost all patients and should be treated prophylactically with laxatives
      • Dry mouth: simple measures e.g. sucking sweets or ice cubes, sips of drink
      • Tolerance and addiction is rarely a problem in palliative care and the need for increasing doses is usually due to progressive disease
    • Alternative strong opioids: diamorphine (3mg oral morphine = 1mg subcutaneous diamorphine), fentanyl, methadone.
  • Adjuvant analgesics may be added at any stage of the ladder. These drugs have a primary indication other than pain but still have an analgesic effect:
    • Corticosteroids, tricyclic antidepressants, anti-convulsants, anti-arrhythmic drugs
  • Difficult Pains: may not respond well to opioids.
    • Neuropathic Pain: from damaged nervous tissue
      • Drugs: Trial of opioids + adjuvant analgesics
        • Tricyclic antidepressants e.g. amitriptyline (increases CNS 5'HT)
        • Anti-convulsants e.g. carbamazepine (decrease nerve excitability)
        • Corticosteroids e.g. dexamethasone (reduces perineural oedema)
      • Non-drug methods
        • TENS: nerve stimulation via surface electrodes
        • Acupuncture
    • Bone Pain: from metastases
      • NSAIDs
      • Radiotherapy: often a single fraction is effective
MediaWiki