Pain and Its Management

INTRODUCTION

Pain is the capital symptom of humans—the great hallmark of disease—the signal par excellence to the patient and doctor that all is not well. In general terms, the origin of conscious pain can be subdivided into three broad types—nociceptive, neurogenic or nociplastic.

1. Nociceptive pain is pain arising from stimulation of superficial or deep tissue pain receptors (nociceptors) from tissue injury or inflammation. It requires an intact nervous system. Nociception is stimulation of peripheral nociceptors (i.e. nerve endings sensitive to a noxious stimulus).

2. Neuropathic pain is pain caused or initiated by a primary lesion or disease or dysfunction (i.e. damage) in the peripheral or central nervous system. It can be subdivided into central pain, when the primary lesion is in the central nervous system (e.g. CVA, MS) or peripheral pain, e.g. postherpetic neuralgia, peripheral neuropathy, trigeminal neuralgia.

3. Nociplastic pain is pain arising from altered nociception despite no evidence of a nociceptive stimulus or lesion of the somatosensory system. It is a diagnosis of exclusion, and central sensitisation is the key contributor. Its experience depends on the affected pathways—it can be variable and non-specific, localised or widespread.

SYSTEMATIC APPROACH TO PAIN HISTORY

Two helpful mnemonics are: SOCRATES—site, onset, character, radiation, alleviating factors, timing, exacerbating factors and severity; and SROT–SARA—site, radiation, onset and offset, type (quality), severity, aggravating factors, relieving factors and associations.

Analgesics in common use

• Paracetamol: oral use

• Aspirin: oral

• Other NSAIDs:

  • – non-selective inhibitors of COX-1 and COX-2 (e.g. ibuprofen, naproxen, indomethacin, ketorolac—oral + IM use)

  • – specific inhibitors of COX-2 (e.g. celecoxib, etoricoxib)

• Opioid analgesics: these agents should be reserved for the treatment of severe, acute pain and palliative pain; routine analgesic use in general practice is discouraged; opioid abuse and dependency is a concern

  • – buprenorphine: sublingual tabs, IM, IV use

  • – codeine: oral

  • – fentanyl: transdermal patches, nasal spray, IM, SC, IV use

  • – hydromorphone: oral, IM, SC, IV use

  • – methadone: oral

  • – morphine: oral, IM, SC, IV use

  • – oxycodone: oral, suppositories

  • – tapentadol: oral use

  • – tramadol: oral, IM, SC injection

Combined analgesics

• Methoxyflurane: an inhalational analgesic (with the Penthrox Inhaler) given in emergency situations such as the roadside. Relief after 8–10 breaths for ~10 mins.

Adjuvants

• Antidepressants: TCAs (e.g. amitriptyline), SNRIs

• Gabapentinoids: gabapentin, pregabalin (side effects often outweigh benefits)

• NMDA blockers: ketamine

• Alpha-2 agonists: clonidine

• Cannabinoids (insufficient evidence)

CHRONIC NON-CANCER PAIN

Evidence is increasingly proving that medication has a minimal role in chronic pain management, in favour of non-pharmacological therapies and active self-management.

Clinical features

• Pain >3 mths or 4 wks longer than the expected time of recovery

• Pain in the absence of ongoing tissue damage

• Central sensitisation:

  • – hyperalgesia

  • – allodynia

Management

The aim ...