Local Anesthetics Series  ·  Module 3 of 4
Clinical Use, Regional Anesthesia Techniques, and Epinephrine
Epinephrine as additive, six anesthesia techniques, differential block, and dose limits
Epinephrine as Vasoconstrictor Additive
Mechanism and Benefits
Why Epinephrine Is Added
  • Alpha-1 receptor activation → vasoconstriction at injection site
  • Slows systemic absorption → prolongs duration of anesthesia
  • Reduces peak plasma concentration → lowers toxicity risk
  • Test dose marker: tachycardia (20+ beats/min rise) signals intravascular injection
  • Standard concentration: 1:200,000 (5 micrograms per milliliter)
Contraindications
When NOT to Add Epinephrine
  • End-artery regions: fingers, toes, penis, tip of nose, ear pinnae — ischemia and necrosis risk
  • Intravenous regional anesthesia (Bier block) — systemic release on tourniquet deflation
  • Severe coronary artery disease or uncontrolled hypertension (relative)
Six Regional Anesthesia Techniques
Technique Overview
From Topical to Neuraxial
Technique Where drug is deposited High-yield facts
Topical Surface of mucosa or skin EMLA cream for intact skin; cocaine for nasal/pharyngeal; tetracaine for eye
Infiltration Directly into tissue at surgical site Most common technique; minor procedures
Peripheral nerve block Adjacent to named nerve or plexus Anesthetizes entire nerve distribution; ultrasound-guided
Epidural Epidural space (outside dura) Catheter allows repeated dosing; slower onset than spinal; labor analgesia
Spinal Subarachnoid space (cerebrospinal fluid) Rapid dense block; single dose; sympathetic block causes hypotension; post-dural puncture headache risk
Intravenous regional (Bier block) Intravenous into exsanguinated, tourniquet-isolated limb Lidocaine only — never bupivacaine; no epinephrine; tourniquet minimum 20 minutes
Differential Block and Dose Limits
Epidural Concentration Effect
Differential Block
  • Low concentration: blocks pain fibers (C and A-delta), preserves motor function — labor analgesia, walking epidural
  • Higher concentration: blocks pain and motor fibers — surgical anesthesia for cesarean section
  • Ropivacaine more motor-sparing than bupivacaine at low concentrations
  • Same drug, different concentration — different clinical outcome
Maximum Dose Limits
Weight-Based Ceiling Doses
  • Lidocaine: ~4–5 mg/kg without epinephrine; ~7 mg/kg with epinephrine
  • Bupivacaine: ~2–3 mg/kg; minimal increase with epinephrine
  • Lower bupivacaine limit reflects severe cardiotoxicity risk
  • Vascular injection sites (intercostal) absorb faster — effectively lower the safe dose
Bier Block Safety Rules
Lidocaine only for intravenous regional anesthesia — never bupivacaine (cardiac arrest risk if tourniquet deflated prematurely). No epinephrine. Tourniquet must remain inflated for minimum 20 minutes. Deflating early releases the full local anesthetic dose into the systemic circulation.