Pain Processing and Adverse Effects

Pain Processing

• Perception of pain experience is influenced by social and environmental cues, as well as cultural conditioning and past personal experiences.

Adverse Effects of Pain

Neuroendocrine

• Activation of stress response
• Poor wound healing
• Impaired immune function
• Hyperglycaemia
• Weight loss / muscle wasting

Musculoskeletal

• Spasms
• Impaired muscle mobility and function
• Immobility
• Weakness
• Fatigue

Psychological

• Anxiety
• Fear
• Sleep deprivation
• PTSD

Cardiovascular

• ↑ heart rate
• ↑ blood pressure
• ↑ myocardial oxygen demand
• Hypercoagulation
• Unstable angina
• Myocardial infarction
• Deep vein thrombosis
• Pulmonary embolism

Respiratory

• ↓ lung volumes
• ↓ cough
• Splinting
• Pneumonia
• Hypoxaemia
• Atelectasis

Gastrointestinal

• ↓ bowel motility
• ↓ gastric emptying
• Constipation
• Anorexia

Pre-Hospital Analgesia

• Hastens the relief of discomfort rather than waiting for pain medication administration in EDs
• Historically only entonox and morphine have been available for pre-hospital pain management
• Many new additions such as Ketamine

Multimodal Approach

• Combines analgesic drugs from different classes and employs analgesic techniques that target different mechanisms of pain
• Inclusive of non-pharmacological therapy
• Its synergistic effect maximizes pain relief at lower analgesic doses
• Reduces the risk of adverse drug effects

Inflammation

• Protective function in response to tissue damage/injury
• Body uses inflammation to destroy invading organisms or irritants, remove toxins and start the process of tissue repair
• Sometimes this inflammation is not appropriate and can become harmful

Prostaglandins

• Huge mediator of the pain response
• Made by all tissues in very small quantities
• Act as local signals to achieve different responses in different tissues
• Two pathways to the production of these mediators:
  • Cyclo-oxygenase Pathway
  • Lipooxygenase Pathway

Pain Assessment

• Use an age-appropriate pain scale to assess pain
• Latest Clinical Practice Guidelines suggest:
  • >12 years: Consider using a self-report scale, such as the Numeric Rating Scale
• Numeric Rating Scale:
  • Preferred due to ease of use and high compliance
  • Designed to help assess the extent of an individual's pain and improve communication regarding pain with health care providers
  • Pros:
    • Takes less than a minute to complete
    • Takes less than a minute to administer and score
    • The numeric scale allows it to be used internationally without translation difficulties
    • Deemed valid and reliable for rating pain intensity
    • Can be administered verbally and in writing, making it accessible for more people
  • Cons:
    • Only evaluates one aspect of pain - intensity
    • Does not factor in past pain experiences
    • Does not factor in fluctuations in pain
    • Only evaluates pain experienced in the last 24 hours or "an average pain intensity"

Analgesic Agents

• Consider the timing of dosing in relation to medication half-life and onset of action
• Mild to moderate pain:
  • Paracetamol (oral / IV)
  • Acetyl salicylic acid
  • Diclofenac
  • Ibuprofen
• Moderate to severe pain:
  • Penthroxyflurane (inhaled)
  • Fentanyl (IV / IN)
  • Morphine (IV)
  • Ketamine (IV / IM / IN)