What is a neuraxial block?

What is Neuraxial Block?

Neuraxial block refers to any epidural, spinal, or combined spinal-epidural (CSE) anesthetic technique that delivers local anesthetic drugs in close proximity to the spinal cord—either intrathecally into the cerebrospinal fluid or epidurally into the fatty tissues surrounding the dura. 1

Core Definition and Scope

Neuraxial anesthesia encompasses three main techniques 1:

• Spinal (intrathecal) block: Direct injection of local anesthetic into the cerebrospinal fluid
• Epidural block: Injection into the epidural space surrounding the dura mater
• Combined spinal-epidural (CSE): Sequential or simultaneous use of both techniques

These techniques can provide either analgesia (pain relief) or complete anesthesia depending on the dose, concentration, and location of drug administration 1, 2.

Clinical Applications

Neuraxial blocks are used across multiple clinical settings 1:

• Obstetric indications: Labor analgesia, cesarean section, operative delivery, cervical suture insertion, or retained placenta removal
• Orthopedic surgery: Lower extremity procedures where neuraxial anesthesia is preferred over general anesthesia 3, 4
• Postoperative pain management: Continuous epidural infusions for up to 72 hours 5
• Chronic pain and spasticity: Intrathecal baclofen for spasticity treatment 2

Mechanism and Pharmacology

Neuraxial techniques work by blocking nerve transmission at the spinal cord level 2:

• Local anesthetics (bupivacaine, ropivacaine, levobupivacaine) provide the primary sensory and motor blockade 5, 2
• Opioids (morphine, fentanyl, sufentanil) are commonly added for enhanced analgesia, particularly in labor epidurals using "low-dose" combinations 1, 2
• Adjuvants such as clonidex, dexmedetomidine, or epinephrine may be added to prolong duration or improve quality of block 2

Key Safety Considerations

Critical Monitoring Requirements

Motor block assessment is the most important safety monitor for detecting serious complications like epidural hematoma, which must be identified within 8-12 hours to prevent permanent neurological damage. 1

For obstetric epidural analgesia during labor 1:

• Hourly motor block monitoring using straight-leg raising (ability to lift heel off bed against gravity)
• Hourly sensory block assessment
• Immediate anesthesiologist notification if unable to perform straight-leg raise

For recovery from spinal or epidural anesthesia 1:

• Inability to straight-leg raise at 4 hours post-last dose requires anesthesiologist assessment and potential escalation

Serious Complications to Monitor

The most feared time-critical complication is vertebral (epidural) hematoma, which requires surgical decompression within 8-12 hours to prevent permanent paralysis 1. Other serious complications include 1:

• Epidural abscess (typically develops over several days)
• Unintended intrathecal or subdural injection causing unexpectedly extensive block
• Arachnoiditis
• Cardiac arrest from extensive regional block

Contraindications

Absolute contraindications include 5:

• Patient refusal
• Active infection at injection site
• Coagulopathy or therapeutic anticoagulation (unless appropriately managed)
• Known hypersensitivity to amide-type local anesthetics

Distinction from Peripheral Nerve Blocks

Neuraxial blocks differ fundamentally from peripheral nerve blocks in that they act centrally at the spinal cord level rather than at peripheral nerves or plexuses. 4 Peripheral blocks (interscalene, femoral, sciatic) inject local anesthetic near specific nerves supplying a surgical area, while neuraxial blocks affect multiple spinal nerve roots simultaneously 3, 4.

Peripheral nerve blocks have fewer physiological side effects compared to neuraxial techniques, as most do not cause sympathectomy-induced hypotension 6. However, neuraxial blocks provide more extensive coverage and are preferred for major lower extremity or abdominal/pelvic procedures 3, 7.

Common Pitfalls

• Delayed recognition of complications: The rarity of serious complications combined with busy clinical environments can lead to missed early warning signs 1
• Inadequate monitoring protocols: Only 56% of UK maternity units had formal neurological monitoring policies in place 1
• Assuming prior spine surgery is a contraindication: While patients with spinal stenosis or prior spine surgery have a slightly higher complication rate (1.1%), neuraxial blocks remain feasible with appropriate patient selection 8
• Failure to have resuscitation equipment available: Lipid emulsion (intralipid) for local anesthetic systemic toxicity must be immediately accessible 5, 3