Study Notes on Regional (Neuraxial) Anesthesia

Study Notes on Regional (Neuraxial) Anesthesia

1. Anesthesia vs Analgesia

• Anesthesia = no sensation (may include unconsciousness, amnesia, analgesia, muscle relaxation).

• Analgesia = no pain (but patient can remain conscious).

• Analgesia is a subset of anesthesia.

• Example: pain meds → analgesia, but NOT anesthesia.

2. Phases of Anesthesia Care

• Preoperative

• Intraoperative

• Postoperative

3. Types of Anesthesia

• General

• Regional (focus today)

• Local

Regional Anesthesia Subtypes

• Neuraxial (spinal, epidural, caudal)

• Limb blocks (to be covered later)

Etymology

• Neuraxial → “neuro” (nervous system) + “axial” (spinal cord lies in body axis).

4. Embryology & Neuroanatomy Refresher

• Ectoderm → nervous system (CNS = neural tube; PNS = neural crest).

• Mesoderm → notochord → nucleus pulposus of intervertebral disc.

• Spinal canal inside spinal cord = CSF-filled central canal.

• Ventricular system: lateral → foramen of Monro → 3rd → aqueduct of Sylvius → 4th → foramen of Magendie (median) & Luschka (lateral) → subarachnoid space.

5. Surface Anatomy & Needle Landmarks

• C7 = most prominent cervical spine.

• Inferior angle of scapula = T7.

• Last rib = L1.

• Iliac crest = L4.

• PSIS = S2.

• Safe lumbar puncture zone: L3–L5 (below spinal cord termination at L1–L2).

• Mnemonic: “To keep the spinal cord alive, keep the needle between L3–5.”

6. Neuraxial Techniques

Spinal Anesthesia

• Needle in subarachnoid space → CSF present.

• Small drug volume needed.

• Fast onset, dense motor & sensory block.

• Higher risk of hypotension & post-dural puncture headache.

Epidural Anesthesia

• Needle in epidural space (outside dura).

• Larger drug volume needed.

• Slower onset, titratable (segmental block).

• Easier to maintain with catheter (continuous infusion).

• More discomfort during insertion.

• Complications: abscess, hematoma, dural puncture (dangerous with large volumes).

7. Layer Sequence for Needle Insertion

Skin → Subcutaneous tissue → Supraspinous ligament → Interspinous ligament → Ligamentum flavum → Epidural space → Dura → Arachnoid → Subarachnoid space (CSF) → Pia.

8. Physiological Effects & Complications

• Hypotension: sympathetic block (loss of vasoconstriction → ↓ venous return → ↓ cardiac output).

• Bradycardia/asystole: unopposed parasympathetic tone.

• Respiratory depression (high block).

• Post-dural puncture headache (PDPH):

  • Onset: 14–18h later.

  • Worse with standing.

  • Mechanism: CSF leak → brain sagging → traction on pain-sensitive structures.

  • Treatment: fluids, analgesics, caffeine IV, epidural blood patch (autologous blood seals leak).

• Urinary retention (blocked bladder sensation).

• Shivering, nausea, itching, back pain.

• Rare: nerve injury, total spinal block, anterior spinal artery syndrome (if artery of Adamkiewicz damaged).

9. Local Anesthetic + Epinephrine in Neuraxial Block

• Epinephrine = vasoconstrictor.

• Benefits:

  1. ↓ Systemic absorption → ↓ toxicity.

  2. ↑ Duration of action.

  3. ↑ Local concentration at nerve.

  4. ↓ Bleeding.

• Especially useful in neuraxial anesthesia.

10. Local Anesthetic Solutions (Baricity)

• Hyperbaric (heavier than CSF) → sinks (use for controlled spread away from surgical site).

• Isobaric (same density as CSF).

• Hypobaric (lighter than CSF) → floats.

• Choice depends on surgery type & patient positioning.

11. Clinical Indications

Spinal anesthesia:

• Lower abdomen, pelvis, perineum, lower limbs.

• NOT for thoracic/upper abdominal surgery.

Epidural anesthesia:

• Same indications as spinal.

• Also used for:

  • Labor & delivery.

  • Postoperative analgesia (continuous infusion).

  • In combination with general anesthesia.

12. Contraindications

• Patient refusal.

• Coagulopathy / bleeding diathesis.

• Local infection at site.

• Raised ICP.

• Allergy to local anesthetic.

• Severe hypovolemia.

13. Key Clinical Pearls

• Sympathetic fibers (small B/C) are blocked first → hypotension is early complication.

• No neuromuscular blocker needed → spinal/epidural itself blocks motor fibers.

• Motor block order: Sympathetic > Sensory > Motor.

• Paresthesia during injection = stop immediately (needle hitting nerve).

• Risk of PDPH higher with younger patients and larger needles.