Local Anesthetics Series  ·  Module 5 of 5
Neuraxial Anesthesia
Spinal versus epidural, neuraxial complications, and obstetric applications
Spinal Versus Epidural — Key Distinctions
Technique 1
Spinal Anesthesia (Subarachnoid Block)
  • Drug injected into cerebrospinal fluid — subarachnoid space
  • Rapid onset — no barrier between drug and nerve roots
  • Dense block — complete sensory and motor blockade
  • Single injection — no catheter in standard use
  • Spread controlled by baricity and patient position
  • Hypotension common from sympathetic block
  • Agents: bupivacaine (preferred), tetracaine
Technique 2
Epidural Anesthesia
  • Drug injected into epidural space — outside dura mater
  • Slower onset — drug diffuses through epidural fat and dura
  • Less dense block — more controllable
  • Catheter allows continuous or repeated dosing
  • Concentration adjusted for labor analgesia vs. surgery
  • Agents: bupivacaine or ropivacaine ± fentanyl
  • Ropivacaine more motor-sparing at low concentrations
Neuraxial Complications
Four Key Complications
Mechanism, Presentation, and Management
Complication Mechanism Presentation Management
Post-dural puncture headache Cerebrospinal fluid leak through dural hole → low intracranial pressure Severe upright, resolves supine (postural headache) Conservative: caffeine, rest. Definitive: epidural blood patch
Transient neurologic symptoms Associated with lidocaine spinal; possible neurotoxicity at nerve roots Back, buttock, leg pain after block resolves; no deficit; self-limiting Supportive; prevention: use bupivacaine instead of lidocaine for spinal
Neuraxial hematoma Bleeding in epidural or subarachnoid space; risk with coagulopathy or anticoagulants Back pain + progressive neurological deficit; bladder or bowel dysfunction Urgent MRI; emergency surgical decompression within 6 to 8 hours
High spinal block Cephalad spread blocks phrenic nerve (cervical nerve roots 3, 4, 5) Respiratory paralysis + severe hypotension Immediate intubation, ventilation, vasopressors
Obstetric Neuraxial Anesthesia
Labor Analgesia
Epidural Catheter Technique
  • Dilute bupivacaine or ropivacaine plus fentanyl infusion
  • Low concentration: sensory block, motor preserved
  • Patient can move, bear weight, push in second stage
  • Ropivacaine preferred: more motor-sparing, less cardiotoxic
  • Early placement does not increase cesarean delivery rate
  • Catheter can be converted to surgical anesthesia if needed
Cesarean Section
Spinal Anesthesia Preferred
  • Hyperbaric bupivacaine intrathecal — rapid dense block
  • Intrathecal fentanyl: intraoperative analgesia
  • Intrathecal morphine: 12 to 24 hours postoperative analgesia
  • Monitor for delayed respiratory depression with intrathecal morphine
  • Urgent cesarean: convert existing epidural with lidocaine or chloroprocaine
  • All local anesthetics cross placenta; fetal acidosis causes ion trapping
Blood Patch — High Yield
Epidural blood patch is the definitive treatment for post-dural puncture headache: 15 to 20 mL of autologous blood injected into the epidural space at the puncture level. Blood clots seal the dural hole and rapidly restore cerebrospinal fluid pressure. Success rate over 90%. Indicated when conservative measures fail within 24 to 48 hours.