Neuraxial Anesthesia

Neuraxial Anesthesia Definition Neuraxial anesthesia refers to regional anesthesia techniques where local anesthetics are injected near the spinal cord to block nerve transmission. It includes:     Spinal anesthesia – Injection into the subarachnoid space. Epidural anesthesia – Injection into the epidural space Combined spinal-epidural (CSE) anesthesia – Combination of both techniques. Caudal epidural anesthesia – A form of epidural anesthesia administered through the sacral hiatus. Advantages of neuraxial anesthesia        Reduced perioperative morbidity and mortality. Reduce respiratory complications in high-risk patients. Reduce cardiac complications in high-risk patients. Allow earlier return of gastrointestinal function following surgery. Provide postoperative analgesia. Reduce bleeding and transfusion requirements. Reduce the incidence of venous thrombosis and pulmonary embolism. Anatomy Relevant to Neuraxial Anesthesia 1. Vertebral Column & Meninges The spinal cord terminates at L1-L2 in adults and L3 in neonates.     Meninges consist of: Dura mater – Outermost, tough layer. Arachnoid mater – Middle layer, contains cerebrospinal fluid (CSF). Pia mater – Innermost layer, adherent to the spinal cord. 2. Spaces in the Vertebral Canal   Epidural space: Between the dura mater and ligamentum flavum, which contains fat and the venous plexus. Subarachnoid space: Between arachnoid and pia mater, contains CSF. The subarachnoid space ends at approximately S2 in adults, lower in children 3. Caudal Epidural Space The sacral hiatus is an opening in the sacrum through which the epidural space can be accessed. Used for caudal epidural anesthesia, primarily in pediatric patients.  The line joining the iliac crests (Tuffier’s line) is approximately at the L4 level. The level of injection (for spinal anesthesia) should be below the level of L2 in adults to avoid spinal cord injury. Types of Neuraxial Anesthesia 1. Spinal Anesthesia (Subarachnoid Block) Site: Injection into the subarachnoid space (L3-L4 or L4-L5). Onset: Rapid (2-5 minutes). Duration: Short-acting (lidocaine) to long-acting (bupivacaine). Uses: Cesarean section, lower limb surgery, urologic surgery. Advantages: Profound sensory and motor block, low drug dose needed. Disadvantages: Hypotension, high spinal risk, post-dural puncture headache (PDPH). 2. Epidural Anesthesia Site: Injection into the epidural space at any level (cervical, thoracic, lumbar, or sacral). Onset: Slower (10-20 minutes). Duration: Prolonged with continuous infusion. Uses: Labor analgesia, thoracic/abdominal surgery, chronic pain. Advantages: Adjustable block level, lower hemodynamic instability. Disadvantages: More complex technique, catheter migration risk. 3. Caudal Epidural Anesthesia Site: Injection into the epidural space via the sacral hiatus. Uses: Pediatrics: Most common regional anesthesia for surgeries below the umbilicus (e.g., hernia repair, circumcision). Adults: Chronic pain management. Advantages: Safe, effective for postoperative pain in children. Disadvantages: Incomplete blockade if misplacement occurs, risk of local anesthetic toxicity. 4. Combined Spinal-Epidural (CSE) Anesthesia Definition: Combination of spinal and epidural anesthesia for rapid onset and prolonged effect. Uses: Labor analgesia, high-risk surgeries. Advantages: Rapid onset with flexibility for prolonged analgesia. Disadvantages: Increased technical complexity. Drugs Used in Neuraxial Anesthesia 1. Local Anesthetics Amides: Bupivacaine, Ropivacaine, Lidocaine. Esters: Tetracaine, Procaine. Mechanism of Action: Block sodium channels → inhibit nerve conduction. 2. Adjuncts Opioids (e.g., fentanyl, morphine) – Enhances analgesia. Epinephrine – Prolongs duration by reducing drug absorption. Clonidine/Dexmedetomidine – Enhances analgesia via α2 agonism. Factors Influencing Level of Spinal Block Complications of Neuraxial Anesthesia 1. Cardiovascular Effects Hypotension: Due to sympathetic blockade. Bradycardia: If T1-T4 cardiac sympathetic fibers are blocked. Prevention: IV fluids, vasopressors (ephedrine, phenylephrine), inotropes (atropine) 2. Neurological Effects Post-Dural Puncture Headache (PDPH): CSF leakage → headache. Nerve Injury: Due to needle trauma, hematoma, and ischemia. 3. Respiratory Effects High Spinal Block: Phrenic nerve paralysis → respiratory depression. 4. Infection & Hematoma Epidural Abscess/Meningitis: Rare, but requires sterile technique. Epidural Hematoma: Risk in patients with coagulopathy.