Pain Management

Pain Fundamentals - Know Thy Foe

• Pain Types:
  • Nociceptive: Due to actual or threatened tissue damage.
    • Somatic: Sharp, dull, aching, well-localized (skin, muscle, bone).
    • Visceral: Deep, cramping, poorly localized (internal organs).
  • Neuropathic: Caused by a lesion or disease of somatosensory nervous system. Burning, shooting, tingling.
• Pain Pathway (Simplified): Transduction → Transmission (Aδ & C fibers) → Perception (CNS) → Modulation (descending inhibition).
• Assessment: Visual Analog Scale (VAS), Numeric Rating Scale (NRS 0-10), Wong-Baker FACES.

⭐ Allodynia (pain from non-painful stimuli) is a hallmark of neuropathic pain.

Multimodal Analgesia - Pain's Kryptonite

• Strategic use of ≥2 analgesic drugs/techniques targeting diverse pain mechanisms.
• Goal: Achieve superior analgesia, significantly ↓ opioid consumption (opioid-sparing) and related side effects.
• Core Elements (📌 PLAN):
  • Paracetamol: Central action.
  • Local/Regional Anesthesia: Nerve blocks, epidurals.
  • Anti-inflammatory drugs: NSAIDs.
  • Narcotics (opioids, judicious use) & Adjuvant Meds: Ketamine, gabapentinoids, lidocaine.
• Benefits: Better pain control, earlier recovery, reduced complications.

⭐ A cornerstone of ERAS (Enhanced Recovery After Surgery) protocols, significantly improving postoperative outcomes.

Non-Opioid Analgesics - Gentle Giants

• Paracetamol (Acetaminophen):
  • Central analgesic, weak COX inhibitor; also antipyretic.
  • Dose: 1g QID (Max 4g/day). IV/PO. Safe therapeutically.
  • Minimal anti-inflammatory. Risk: Hepatotoxicity (overdose, alcohol).

  ⭐ Antidote for paracetamol overdose: N-acetylcysteine (NAC), most effective within 8-10h.

• NSAIDs (Non-Steroidal Anti-Inflammatory Drugs):
  • COX inhibitors (↓ prostaglandins). Analgesic, anti-inflammatory, antipyretic; opioid-sparing.
  • Types: Non-selective (Ibuprofen); COX-2 selective (Etoricoxib - ↓GI toxicity, CV risk persists).
  • Risks: GI ulcers/bleed, renal injury (AKI), ↑CV events, platelet dysfunction.
  • Ketorolac: Potent injectable, max 5 days (GI/renal toxicity).
  • Avoid: PUD, renal/heart failure, AERD, pregnancy (3rd trimester).

Opioid Analgesics - Potent Power

• Mechanism: Act on μ, κ, δ opioid receptors (CNS, periphery).
• Strong Agonists:
  • Morphine: Gold standard.
  • Fentanyl: Potent (80-100x morphine), rapid, short-acting.
  • Pethidine: Shorter acting; risk of seizures (norpethidine).
  • Methadone: Long half-life; for opioid dependence.
• Atypical: Tramadol (weak μ-agonist, SNRI).
• Antagonist: Naloxone (reverses opioid overdose).
• Side Effects: Respiratory depression (⚠️), sedation, miosis (📌 except Pethidine), constipation, N/V, dependence.

⭐ Fentanyl patches: for chronic pain in opioid-tolerant patients; high risk of fatal hypoventilation if misused.

Regional & PCA - Precision Pain Punishers

• Regional Anesthesia: Targeted pain relief.
  • Types: Epidural, spinal, peripheral nerve blocks (e.g., brachial plexus, femoral).
  • Pros: Superior analgesia, opioid-sparing, ↓ PONV, ↓ ileus, early mobilization.
  • Cons: Hypotension (esp. neuraxial), PDPH, nerve injury, hematoma, infection.
• Patient-Controlled Analgesia (PCA): Empowers patients.
  • Mechanism: Patient self-administers small, preset opioid doses (IV, epidural).
  • Settings: Bolus dose, lockout interval (e.g., 5-10 min), +/- basal rate (caution!).
  • Drugs: Morphine, Fentanyl, Hydromorphone.
  • Monitor: RR, SpO2, sedation.

⭐ PCA is contraindicated in patients unable to understand or operate the device (e.g., very young, cognitively impaired).

High‑Yield Points - ⚡ Biggest Takeaways

• Multimodal analgesia is standard: combine opioids, NSAIDs, paracetamol, and regional blocks.
• Adhere to the WHO analgesic ladder for a structured approach to pain relief.
• PCA (Patient-Controlled Analgesia) with opioids like morphine enhances patient comfort.
• Epidural analgesia provides superior pain control post major abdominal/thoracic surgery.
• NSAIDs are potent analgesics; monitor for renal, GI, and bleeding risks.
• Paracetamol is a fundamental, safe analgesic; maximum daily dose is 4g.
• Consider gabapentinoids for neuropathic pain and as opioid-sparing agents.