Clinical Uses of Local Anesthetics

Clinical Uses: LA Application Routes - Numbness Delivery

• Topical Anesthesia:
  • Applied to skin or mucous membranes (cornea, throat, urethra).
  • Forms: Sprays, gels, creams, ointments.
  • Agents: Lidocaine, tetracaine, benzocaine.

  ⭐ EMLA (Eutectic Mixture of Local Anesthetics): Lidocaine 2.5% + Prilocaine 2.5%. Minimum application time: 60 minutes on intact skin.

• Infiltration Anesthesia:
  • Direct injection into tissues for localized numbness.
  • Uses: Suturing, wound cleaning, minor excisions, dental procedures.
  • Field block: LA injected around the target area.
• Intravenous Regional Anesthesia (IVRA - Bier's Block):
  • LA injected into an exsanguinated limb, isolated by a tourniquet.
  • Provides anesthesia for limb surgery (e.g., forearm, hand).

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Clinical Uses: Nerve Block Techniques - Pinpoint Anesthesia

• Peripheral Nerve Blocks (PNBs): Target specific nerves/plexuses for localized anesthesia & analgesia.
  • Upper Limb: Brachial plexus (Interscalene, Supraclavicular, Axillary); Median, Ulnar, Radial nn.
  • Lower Limb: Femoral, Sciatic (Popliteal, Ankle), Obturator nn.
  • Trunk: Intercostal, Paravertebral, TAP blocks.
  • Head & Neck: Trigeminal branches, Cervical plexus.
• Guidance Techniques:
  • Landmark-based: Relies on anatomical knowledge.
  • Peripheral Nerve Stimulator (PNS): Elicits motor response to confirm proximity.
  • Ultrasound Guidance (USG): Real-time visualization of nerve & needle; ↑success, ↓complications. Gold Standard.
• Central Neuraxial Blocks (CNBs): More regional; can be targeted (e.g., segmental spinal/epidural).
  • Spinal: Anesthesia via subarachnoid LA injection.
  • Epidural: Analgesia/anesthesia via epidural LA; catheter for continuous/bolus.

⭐ Order of sensory/functional loss in PNBs: Sympathetic block (vasodilation, temp ↑) → Pain & Temperature (Aδ, C fibers) → Proprioception (Aγ) → Touch & Pressure (Aβ) → Motor function (Aα). 📌 Mnemonic: Some People Prefer Touching Motors.

Clinical Uses: Beyond Surgical Fields - LA's Versatile Roles

• Acute & Chronic Pain Management:
  • Post-operative analgesia: wound infiltration, continuous nerve blocks.
  • Chronic pain: neuropathic pain, cancer pain (nerve/epidural blocks).
  • Labor analgesia: epidural, spinal.
• Cardiac Arrhythmias:
  • Ventricular tachyarrhythmias.

  ⭐ Lidocaine is a Class Ib antiarrhythmic, used for ventricular tachycardia. Typical IV bolus: 1-1.5 mg/kg, followed by infusion 1-4 mg/min.

• Diagnostic Procedures:
  • Nerve blocks to pinpoint pain origin.
• Other Specialized Uses:
  • Topical anesthesia: mucous membranes (e.g., bronchoscopy).
  • Sympathetic blockade: e.g., Complex Regional Pain Syndrome (CRPS).
  • Antitussive: nebulized lidocaine for intractable cough.
  • Anti-inflammatory properties (emerging evidence).

Clinical Uses: Clinical Safety Net - LA Caveats & Care

• ⚠️ Max Dose Adherence: Critical. Calculate per LA, weight, site.
• Vasoconstrictors (Epinephrine):
  • Pros: Prolongs action, ↓systemic absorption & bleeding.
  • Cons: Risk of ischemia in end-arterial zones (fingers, toes, nose, penis); systemic effects.
• Patient Factors:
  • Liver disease: Impairs amide metabolism.
  • Pseudocholinesterase deficiency: Prolongs ester LA action.
• LAST (Local Anesthetic Systemic Toxicity):
  • CNS excitation (tinnitus, seizures) → CNS depression → CVS toxicity.

  ⭐ Initial bolus dose of lipid emulsion (20%) for LAST: 1.5 mL/kg over 1 min. Max total 3 mL/kg.

• Other Complications:
  • Allergy: Rare (esters > amides; PABA).
  • Methemoglobinemia: Prilocaine, Benzocaine. Tx: Methylene Blue.

High‑Yield Points - ⚡ Biggest Takeaways

• Topical anesthesia: For mucous membranes (airway) & skin (EMLA).
• Infiltration: Direct tissue injection for minor surgeries.
• Peripheral Nerve Blocks: Target specific nerves/plexuses for limb surgery.
• Spinal Anesthesia: Subarachnoid injection for rapid, dense surgical block.
• Epidural Anesthesia: For labor analgesia & post-op pain control.
• IVRA (Bier's Block): For short limb surgeries using a tourniquet.
• Lidocaine: Systemically for ventricular arrhythmias; also in chronic pain blocks.