Pain Overview

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Pain is:

Pain Assessment

Use the PASS assessment:

  • Pain history
    • Somatic
    • Neuropathic
  • Analgesia and other drug substances
  • Stress and other psychology
  • Surgical factors and biological causes

Key components of a pain history include:

  • Site
    • Location
    • Radiation
  • Circumstances
    Associated trauma, procedures.
  • Character
    Key descriptors.
  • Intensity
    Including:
    • At rest
    • With movement
    • Temporal factors
      • Duration
      • Intensity over time
      • Continuous or intermittent
    • Aggravating or relieving factors
  • Associated symptoms
  • Effect of pain on:
    • Activities of daily living
    • Sleep
  • Treatment
    • Current and previous medications
      • Doses
      • Frequency of use
      • Efficacy
      • Adverse effects
    • Other treatment
    • Health professionals consulted
  • Relevant medical history
  • Factors influencing patients symptomatic treatment
    • Belief around cause
    • Knowledge, expectations, and preferences for management
    • Expected outcome
    • Reduction in pain required for patient satisfaction
    • Coping responses
    • Family expectations

Pain Management

Goals of pain management include:

  • ↓ Pain initiation
  • Inhibit neurotransmission
  • Prevent sensitisation
    • Central
    • Peripheral
  • Psychological preparation
    • Set expectations
    • Control pain

Mechanism-Based Approach

A mechanism-based approach uses a combination of agents to interrupt nociception at multiple levels of the pain fibre. In general, consider:

Key terms:

  • Preventative analgesia
    Analgesic effect lasts longer than expected duration of drug effet.
  • Preemptive analgesia
    Analgesia provided prior to nociceptive stimulus.
  • Allergies and drug intolerances
  • Pre-existing pain syndrome or drug exposure
  • Nature of painful stimulus
    • Expected duration
    • Expected magnitude
  • Available routes of administration

Then consider an escalating level of:

  • Single analgesia
    • Paracetamol
    • NSAID if appropriate
  • Regional techniques (or epidural)
  • Non-pharmacological adjuncts
  • Requirement for an antineuropathic
  • Short-acting opioid
    • Oral PRN
      • Oxycodone
      • Morphine
    • Sublingual PRN
      • Buprenorphine
    • IV PCA
      • Oxycodone
      • Morphine
      • Fentanyl
      • Buprenorphine
  • Pharmacological adjuncts
    • Ketamine infusion
    • Lignocaine infusion
    • Clonidine
  • Regular opioid

Situation-Based Approach

A situation-based approach is used when the presentation fits a particular pain syndrome.

Acute Neuropathic Pain

  • First line
    • Ketamine
      • Titrate up with 5mg boluses to effect
      • Maintain at 0.1mg/kg/hr IV or SC infusion
  • Second line
    • Lignocaine
      • Bolus 1-1.5mg/kg
      • Maintain at 1-2mg/min

Chronic Neuropathic Pain

  • First line
    • TCAs
      • Commence at 5-10mg and ↑ slowly to optimise acceptability
      • Effective dose usually 10-100mg
      • Slow onset and trial for at least 2 weeks, and ideally 2 months
      • Amitryptyline superior if sleep disturbance an issue; give nocte
      • Nortriptyline less sedating
      • Adverse effects significant
    • SSRIs/SNRIs
      • Duloxetine 30mg daily, ↑ up to 60mg
      • Venlafaxine 37.5mg, ↑ to 75mg, up to 225mg daily
  • Second line
    α2-delta ligands:
    • Pregabalin
      75mg up to 300mg BD, start at 25-50mg if frail.
    • Gabapentin
  • Third line
    • Tramadol
    • Tapentadol

Phantom Limb Pain

  • First line
    • Calcitonin
      100ug daily SC/ for at least 3 days. Antiemetic prophylaxis.
  • Second line
    Antineuropathics as above.

References

  1. Schug SA, Palmer GM, Scott DA, Alcock M, Halliwell R, Mott JF; APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine (2020), Acute Pain Management: Scientific Evidence (5th edition), ANZCA & FPM, Melbourne.
  2. Rigg JR, Jamrozik K, Myles PS, Silbert BS, Peyton PJ, Parsons RW, et al. Epidural anaesthesia and analgesia and outcome of major surgery: a randomised trial. The Lancet. 2002 Apr 13;359(9314):1276–82.
  3. N. Meylan, N. Elia, C. Lysakowski, M. R. Tramèr. Benefit and risk of intrathecal morphine without local anaesthetic in patients undergoing major surgery: meta-analysis of randomized trials. BJA: British Journal of Anaesthesia, Volume 102, Issue 2, 1 February 2009, Pages 156–167.
  4. McLeod GA, Cumming C. Thoracic epidural anaesthesia and analgesia. Continuing Education in Anaesthesia Critical Care & Pain, Volume 4, Issue 1, 1 February 2004, Pages 16–19.
  5. Schug SA, Palmer GM, Scott DA, Halliwell R, Trinca J. Acute pain management: scientific evidence, fourth edition, 2015. Med J Aust. 2016 May 2;204(8):315–7.
  6. Russell T, Mitchell C, Paech MJ, Pavy T. Efficacy and safety of intraoperative intravenous methadone during general anaesthesia for caesarean delivery: a retrospective case-control study. International Journal of Obstetric Anesthesia. 2013 Jan;22(1):47–51.
  7. Western Australian Therapeutic Advisory Group. Guidelines for the Pharmacological Treatment of Neuropathic Pain. 2017.