Neuraxial Anesthesia

Spinal versus epidural, neuraxial complications, and obstetric applications

Spinal and epidural anesthesia are anatomically distinct techniques that share the same drug class but produce pharmacologically different results. The subarachnoid space contains cerebrospinal fluid with no intervening tissue between the drug and the nerve roots — onset is rapid and the block is dense. The epidural space is separated from the nerve roots by dura and epidural fat — onset is slower, the block is more controllable, and a catheter can be placed for continuous dosing.

The density difference between the two techniques is not merely a matter of degree; it determines their clinical applications. Dense complete blockade from a spinal is exactly what surgical anesthesia requires. The controllable, concentration-adjustable block of an epidural catheter is what labor analgesia requires — where eliminating pain without eliminating motor function is the goal, and the clinical need may evolve over many hours.

The complications table covers the four complications with the highest examination yield. Post-dural puncture headache is postural — upright worsens it, supine relieves it — because the dural hole allows cerebrospinal fluid to leak and intracranial pressure falls when upright. That postural character is the diagnostic test. Transient neurologic symptoms from lidocaine spinal are self-limiting but are the reason bupivacaine has largely replaced lidocaine for intrathecal use.

Neuraxial hematoma is the most consequential complication: a space-occupying bleed in the epidural or subarachnoid space compresses the spinal cord. The window for surgical decompression is 6 to 8 hours. Back pain with progressive neurological deficit — especially bladder or bowel dysfunction — is the red flag constellation. The risk is elevated in patients on anticoagulants, which is why published guidelines govern the timing relationship between anticoagulation and neuraxial procedures.

The obstetric section closes the chapter by applying both techniques to their most common clinical setting. Labor epidural uses dilute concentration for differential block. Cesarean section uses intrathecal hyperbaric bupivacaine for dense rapid blockade, with intrathecal morphine providing prolonged postoperative analgesia — at the cost of delayed respiratory depression monitoring, which is the safety trade-off that must be understood alongside the benefit.

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.

Author / Organization	Title	Source
Katzung BG, ed.	Basic and Clinical Pharmacology. 15th ed.	McGraw-Hill; 2021
Brunton LL, Knollmann BC, eds.	Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed.	McGraw-Hill; 2023
Butterworth JF, Mackey DC, Wasnick JD, eds.	Morgan and Mikhail's Clinical Anesthesiology. 6th ed.	New York: McGraw-Hill; 2018:937–992
Gehling M, Tryba M	Risks and side-effects of intrathecal morphine combined with spinal anesthesia: a meta-analysis	Anaesthesia. 2009;64(6):643–651
Apfel CC, Saxena A, Cakmakkaya OS, Gaiser R, George E, Radke O	Prevention of postdural puncture headache after accidental dural puncture: a quantitative systematic review	Br J Anaesth. 2010;105(3):255–263
Carvalho B, Durbin M, Drover DR, Cohen SE, Ginosar Y, Riley ET	The incidence of motor block with 0.125% versus 0.0625% bupivacaine with fentanyl for labor epidural analgesia	Anesth Analg. 2003;96(5):1468–1472
Horlocker TT, Vandermeuelen E, Kopp SL, Gogarten W, Leffert LR, Benzon HT	Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy	Reg Anesth Pain Med. 2018;43(3):263–309
Ilfeld BM	Continuous peripheral nerve blocks: a review of the published evidence	Anesth Analg. 2011;113(4):904–925
Guay J, Nishimori M, Kopp S	Epidural local anesthetics versus opioid-based analgesic regimens for postoperative gastrointestinal paralysis, vomiting and pain after abdominal surgery	Cochrane Database Syst Rev. 2016;7:CD001893
Hadzic A, ed.	Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia. 2nd ed.	New York: McGraw-Hill; 2011
Rosenberg PH, Veering BT, Urmey WF	Maximum recommended doses of local anesthetics: a multifactorial concept	Reg Anesth Pain Med. 2004;29(6):564–575

Author / Organization

Title

Source

Katzung BG, ed.

Basic and Clinical Pharmacology. 15th ed.

McGraw-Hill; 2021

Brunton LL, Knollmann BC, eds.

Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed.

McGraw-Hill; 2023

Butterworth JF, Mackey DC, Wasnick JD, eds.

Morgan and Mikhail's Clinical Anesthesiology. 6th ed.

New York: McGraw-Hill; 2018:937–992

Gehling M, Tryba M

Risks and side-effects of intrathecal morphine combined with spinal anesthesia: a meta-analysis

Anaesthesia. 2009;64(6):643–651

Apfel CC, Saxena A, Cakmakkaya OS, Gaiser R, George E, Radke O

Prevention of postdural puncture headache after accidental dural puncture: a quantitative systematic review

Br J Anaesth. 2010;105(3):255–263

Carvalho B, Durbin M, Drover DR, Cohen SE, Ginosar Y, Riley ET

The incidence of motor block with 0.125% versus 0.0625% bupivacaine with fentanyl for labor epidural analgesia

Anesth Analg. 2003;96(5):1468–1472

Horlocker TT, Vandermeuelen E, Kopp SL, Gogarten W, Leffert LR, Benzon HT

Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy

Reg Anesth Pain Med. 2018;43(3):263–309

Ilfeld BM

Continuous peripheral nerve blocks: a review of the published evidence

Anesth Analg. 2011;113(4):904–925

Guay J, Nishimori M, Kopp S

Epidural local anesthetics versus opioid-based analgesic regimens for postoperative gastrointestinal paralysis, vomiting and pain after abdominal surgery

Cochrane Database Syst Rev. 2016;7:CD001893

Hadzic A, ed.

Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia. 2nd ed.

New York: McGraw-Hill; 2011

Rosenberg PH, Veering BT, Urmey WF

Maximum recommended doses of local anesthetics: a multifactorial concept

Reg Anesth Pain Med. 2004;29(6):564–575