Pain Management in Emergency

Pain Assessment & Principles - Ouch Meter!

⭐ Pain is the "Fifth Vital Sign". Prompt assessment & management are critical in emergencies.

• Define Pain: Unpleasant sensory/emotional experience associated with actual/potential tissue damage.
• Types: Nociceptive (somatic, visceral), Neuropathic (nerve injury).
• Assessment Tools:
  • 📌 PQRST mnemonic: Provocation/Palliation, Quality, Region/Radiation, Severity, Timing.
  • Scales: Numeric Rating Scale (NRS 0-10), Visual Analog Scale (VAS), Wong-Baker FACES (children), FLACC (non-verbal).
• Stepwise Analgesia (WHO Ladder Adaptation):

• Principles: Treat early, use multimodal approach (combine drug classes), titrate to effect.

Non-Opioid Analgesics - Gentle Giants

• Paracetamol (PCM)
  • MOA: CNS prostaglandin inhibitor.
  • Use: Pain, fever.
  • Dose: 1g q6h (Max 4g/day).
  • ⚠️ Hepatotoxic: >10g or >150mg/kg.
• NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)
  • MOA: COX inhibition.
  • Use: Pain, inflammation.
  • CI: Peptic ulcer, renal/HF, asthma, 3rd trim preg.
  • SE: GI bleed, renal tox, CV risk. 📌 No ulcers, Sticky blood, Asthma, Impaired renal, During pregnancy (avoid 3rd trim).
  • Examples (Max daily):
    • Ibuprofen: 400-600mg q6h (2.4g).
    • Diclofenac: 50mg q8h (150mg).
    • Ketorolac: 15-30mg IV q6h (120mg, ≤5 days).
    • Mefenamic Acid: 250-500mg q8h (1.5g).

  ⭐ Ketorolac: Opioid-level analgesia (renal colic); use ≤5 days (GI/renal risk).

Opioid Analgesics - Mighty Morphers

Mechanism: Bind to μ (primary), κ, δ opioid receptors in CNS & periphery, modulating pain perception. For severe acute pain.

• Key Opioids (IV Route in ER):
  • Morphine: Gold standard. Onset 5-10min, duration 3-4h.
  • Fentanyl: Potent (80-100x Morphine). Onset 1-2min, duration 30-60min.
  • Pethidine: Less potent than Morphine. Risk of norpethidine toxicity (seizures), esp. renal failure. (75-100mg IM ≈ Morphine 10mg IM).
• Side Effects (SE): Respiratory depression (monitor!), N/V, sedation, constipation, miosis. 📌 MORPHINES (common side effects).
• Reversal: Naloxone 0.4-2mg IV, repeat q2-3min (max 10mg). Titrate to reverse respiratory depression, not analgesia.

⭐ > Fentanyl's rapid onset and short duration make it ideal for procedural sedation and analgesia.

Local Anesthesia & Blocks - Numb Zone

• Mechanism: Reversibly block $Na^+$ channels in nerve membranes, inhibiting action potential propagation.

• Common ER Blocks: Digital nerve block (fingers/toes), dental blocks (inferior alveolar), wound infiltration for suturing, hematoma blocks for fracture reduction.

• Key Agents:

  Agent	Onset	Duration	Max Dose (Plain)	Max Dose (+Adrenaline)	Notes
  Lidocaine	Rapid	Mod (1-2h)	4.5mg/kg	7mg/kg	Versatile, common
  Bupivacaine	Slower	Long (4-8h)	2mg/kg	2.5mg/kg	Potent, ↑cardiotoxicity risk

• LA Systemic Toxicity (LAST):

  • Early: Tinnitus, metallic taste, perioral numbness.
  • 📌 SAMS: Slurred speech, Altered CNS (agitation, drowsiness), Muscle twitching, Seizures.
  • Severe: Arrhythmias, cardiovascular collapse.
  • Management: Stop LA, ABCs (airway, O2), IV Benzodiazepines for seizures.

⭐ Lipid emulsion therapy (Intralipid 20%) is the specific antidote for severe LAST, especially with Bupivacaine.

Adjuncts & Special Cases - Tricky Treats

• Ketamine: Dissociative analgesia.
  • Sub-dissociative (pain): 0.1-0.3 mg/kg IV.
  • Procedural sedation: 1-2 mg/kg IV.

⭐ Sub-dissociative dose ketamine provides effective analgesia without significant psychomimetic side effects or respiratory depression.

• Nitrous Oxide (N₂O): Rapid inhalational analgesia (e.g., Entonox 50:50).
• Adjuvants: Benzodiazepines (muscle spasm); Antiemetics (nausea).
• Special Populations:
  • Pediatrics: Strict weight-based dosing; paracetamol preferred.
  • Geriatrics: ↓ doses (polypharmacy, ↓ metabolism).
  • Pregnancy: Paracetamol safe; NSAIDs avoid (3rd trimester).

High‑Yield Points - ⚡ Biggest Takeaways

• Opioids (morphine, fentanyl) for severe acute pain; monitor respiratory depression.
• NSAIDs (ketorolac) for mild-moderate pain (musculoskeletal); risk GI bleed, renal injury.
• Paracetamol for mild-moderate pain & as adjunct; hepatotoxicity in overdose.
• Low-dose ketamine: potent analgesia without respiratory depression; ideal for trauma.
• Regional nerve blocks: targeted pain relief, reduce systemic opioid needs.
• Nitrous oxide: rapid analgesia/anxiolysis for short painful procedures.
• Always assess pain score (VAS) and reassess post-intervention_._