Overview
This lecture covers key concepts in pain definitions, physiology, assessment, pharmacological management, and special considerations in chronic and neuropathic pain, providing important exam-focused knowledge.
Pain Definitions & Types
- Pain is an unpleasant sensory and emotional experience related to actual or potential tissue damage.
- Acute pain is recent onset; chronic pain lasts three months or more.
- Pain is subjective and must be accepted based on the patient's report.
Pain Physiology
- Pain has sensory (physical sensation) and affective (emotional response) components.
- Pain threshold is the point at which a stimulus is perceived as painful; pain tolerance is the individual's response to pain.
- Pain is carried by C fibers (slow, dull pain) and A delta fibers (fast, sharp pain).
- Pain can be experienced without nerve signals, and nerve signals may not always cause pain.
- Referred pain is felt in an area different from the injury site (e.g., left arm pain in heart attack).
- Neuropathic pain results from dysfunctional or damaged nerves, often with burning or tingling sensations.
Pain Assessment
- Pain is measured subjectively using tools like the Visual Analog Scale (VAS) and Numerical Rating Scale (NRS).
- For children or those with learning difficulties, face-based graphical scales are used.
Analgesic Ladder & Pain Medications
- WHO analgesic ladder: Step 1—non-opioids (paracetamol, NSAIDs); Step 2—weak opioids (codeine, tramadol); Step 3—strong opioids (morphine, fentanyl).
- Adjuvants for neuropathic pain include amitriptyline, duloxetine, gabapentin, pregabalin, and capsaicin cream.
Side Effects & Contraindications
- NSAIDs cause gastritis, ulcers, asthma, hypertension, kidney and heart problems; contraindicated in specific risks.
- Opioids cause constipation, pruritus (itching), nausea, confusion, sedation, and respiratory depression; naloxone reverses opioid overdose.
Opioid Use in Palliative Care
- Background opioids are given regularly; rescue doses for breakthrough pain are one-sixth of total daily dose.
- Opioid conversions: 10mg oral morphine ≈ 100mg codeine/tramadol, 6.6mg oxycodone, 5mg IV morphine, 3mg IV diamorphine.
Post-Operative & Patient-Controlled Analgesia
- Post-operative pain management includes regular paracetamol, NSAIDs, opioids, and local anesthetics.
- Patient-controlled analgesia (PCA) allows patients to self-administer IV opioids; only patients should press the button.
Chronic Pain
- Chronic primary pain (no clear cause) and chronic secondary pain (identifiable cause).
- Management of primary chronic pain: exercise, ACT, CBT, acupuncture, antidepressants (not analgesics).
- Chronic secondary pain: stepwise approach—paracetamol/topical NSAIDs, oral NSAIDs, opioids if necessary.
Neuropathic Pain
- DN4 questionnaire helps diagnose neuropathic pain (score ≥4).
- First-line drugs: amitriptyline, duloxetine, gabapentin, pregabalin (trial one at a time).
- Trigeminal neuralgia: first-line is carbamazepine; refer if ineffective.
Key Terms & Definitions
- Allodynia — pain from stimuli not normally painful.
- Nociceptors — pain receptors at nerve endings.
- Analgesic ladder — stepwise approach to pain medication.
- Rescue dose — extra opioid dose for breakthrough pain, one-sixth of daily dose.
- Neuropathic pain — pain from nerve dysfunction/damage.
Action Items / Next Steps
- Review local pain management guidelines.
- Remember opioid dose calculations and conversions for exams.
- Read NICE 2021 guidelines for chronic pain management.