Acute Pain Management

Acute Pain Management: Intro & Assessment - Ouch Meter Reading

• Acute Pain: Sudden onset, typically <3 months, direct result of tissue injury. Serves a protective biological function.
  • Types: Nociceptive (somatic, visceral), Neuropathic.
• Pain Assessment: Crucial for diagnosis, guiding treatment, and monitoring efficacy.
  • PQRST Mnemonic (📌): Provocation/Palliation, Quality, Radiation, Severity, Timing.
  • Self-Report Scales (Gold Standard):
    • Numeric Rating Scale (NRS): Score 0 (no pain) to 10 (worst imaginable pain).
    • Visual Analog Scale (VAS): 100mm line, patient marks pain level.
    • Faces Pain Scale-Revised (FPS-R): For children or those with communication difficulties.
  • Behavioral Scales (Non-verbal patients):
    • FLACC Scale: Face, Legs, Activity, Cry, Consolability (children 2 months - 7 years).
    • CPOT: Critical-Care Pain Observation Tool (adult ICU patients).

⭐ Self-report of pain is the most reliable indicator; always attempt to elicit it if possible, even in challenging patient populations (e.g., mild cognitive impairment).

Acute Pain Management: Pharmacotherapy - Painkiller Parade

• WHO Analgesic Ladder: Guides drug selection.

• Non-Opioids:
  • Paracetamol (PCM): Analgesic, antipyretic. Max 4g/day. Risk: Hepatotoxicity.
  • NSAIDs (e.g., Ibuprofen, Diclofenac): COX inhibitors; anti-inflammatory.
    • Max: Ibuprofen 2.4g/day, Diclofenac 150mg/day.
    • S/E: GI ulcers, renal toxicity, ↑CV risk. 📌 NSAID: No pee, Stomach ulcers, Asthma, Increased bleeding, Dyspepsia.
• Weak Opioids:
  • Tramadol: Max 400mg/day. SNRI activity; lowers seizure threshold.
  • Codeine: Prodrug (CYP2D6 to morphine); antitussive.
• Strong Opioids: Morphine, Fentanyl, Pethidine.
  • Morphine: Gold standard. Oral:IV approx 1:3. Active metabolites M6G (analgesic), M3G (neurotoxic).
  • Fentanyl: Potent (80-100x morphine). IV, transdermal; rapid onset, short duration.
  • Pethidine: Norpethidine (neurotoxic metabolite). Max 600mg/24h for <48h. Avoid in renal failure/elderly.
  • S/E: Nausea, vomiting, constipation, sedation, respiratory depression (reverse with Naloxone).
• Adjuvants: Enhance analgesia or treat specific pain types.
  • e.g., Gabapentinoids (Gabapentin, Pregabalin) for neuropathic pain; Amitriptyline (TCA); Ketamine (NMDA antagonist) for opioid-sparing.

⭐ Pethidine is contraindicated with MAO inhibitors due to high risk of serotonin syndrome or hypertensive crisis.

Acute Pain Management: Regional Techniques - Zone Defense

• Goal: Localized analgesia by blocking nerve transmission.
• Peripheral Nerve Blocks (PNBs):
  • Upper Limb: Interscalene, Supraclavicular, Axillary (Brachial Plexus).
  • Lower Limb: Femoral, Sciatic, Popliteal.
  • Truncal: TAP (Transversus Abdominis Plane), Paravertebral, Intercostal.
• Neuraxial Analgesia:
  • Epidural: Thoracic/Lumbar; continuous via catheter.
  • Spinal (Intrathecal): Single shot; rapid, dense block.
• Agents: Local Anesthetics (e.g., Bupivacaine, Ropivacaine); Adjuvants (e.g., epinephrine, dexmedetomidine) prolong duration.
• Benefits: Superior pain relief, opioid-sparing, ↓PONV (Postoperative Nausea and Vomiting), early mobilization.
• Risks: LAST (Local Anesthetic Systemic Toxicity), nerve injury, hematoma, infection.

⭐ Epidural analgesia is a gold standard for labor analgesia and post-thoracotomy pain.

• 📌 LAST early CNS signs: Metallic taste, Numbness (oral/tongue), Tinnitus, Dizziness, Visual disturbances (Mnemonic: My New Telephone Doesn't Vibrate).

Acute Pain Management: Special Contexts & Adjuncts - Tricky Pains & Tricks

• Special Contexts: Post-op (ERAS), Trauma, Burns, Pancreatitis.
• Key Adjuncts (Multimodal Analgesia - MMA):
  • Ketamine (low-dose): 0.1-0.3 mg/kg IV; anti-hyperalgesic, useful in opioid tolerance.
  • Gabapentinoids (Gabapentin, Pregabalin): Neuropathic pain component.
  • IV Lidocaine: 1-2 mg/kg/hr (max 3-5 mg/kg); anti-inflammatory, Na+ channel blocker.
  • Alpha-2 agonists (Dexmedetomidine, Clonidine): Opioid-sparing.
• Tricky Pains: Neuropathic pain, Opioid-tolerant patients, Opioid-Induced Hyperalgesia (OIH).
• Tricks & Strategies:
  • Preventive & preemptive analgesia.
  • Regional anesthesia/analgesia (nerve blocks, epidurals).
  • Non-pharmacological: TENS, cryotherapy.

⭐ Low-dose ketamine infusion is a valuable adjunct in managing acute pain in opioid-tolerant patients and can prevent OIH.

High‑Yield Points - ⚡ Biggest Takeaways

• Multimodal analgesia is key: combines NSAIDs, opioids, paracetamol, and regional techniques.
• NSAIDs (e.g., Ketorolac): potent; watch for renal, GI, and bleeding risks.
• Opioids (Morphine, Fentanyl): for severe pain; monitor respiratory depression, sedation, PONV.
• Paracetamol: safe baseline analgesic; vital in multimodal regimens. Max dose 4g/day.
• Regional anesthesia (epidurals, nerve blocks): superior pain relief, opioid-sparing, better outcomes.
• PCA (Patient-Controlled Analgesia): empowers patients, effective opioid titration, improves satisfaction.
• Ketamine (low-dose) and Gabapentinoids are useful adjuncts, reducing opioid needs.