Components of an Epidural
An epidural consists of a catheter placed in the epidural space through which local anesthetics (primarily bupivacaine, lidocaine, or chloroprocaine) are administered, typically combined with opioids (fentanyl or morphine) and increasingly with adjuvant medications such as alpha-2 agonists (clonidine or dexmedetomidine).
Anatomical Space
The epidural space is a real anatomic compartment located outside the dura mater within the spinal canal, extending from the foramen magnum to the sacrum 1. This space contains:
- Epidural fat deposited posteriorly in a recess between the ligamenta flava 2
- Internal vertebral venous plexus 2
- Spinal nerve roots 1
- Epidural arteries 1
- Thin layer of areolar connective tissue that allows displacement of the dural sac during spinal movement and venous engorgement 2
The posterior epidural space is divided by the plica mediana dorsalis and additional transverse connective tissue planes, creating a compartmentalized structure 3.
Pharmacological Components
Primary Local Anesthetics
Bupivacaine is an amide-type local anesthetic with intermediate to long duration, administered epidurally in isobaric formulation at low concentrations for labor epidural analgesia 4.
Lidocaine is an intermediate-acting amide-type local anesthetic with intermediate onset when given epidurally, most commonly used for intrapartum cesarean delivery 4. Its onset can be shortened by adding sodium bicarbonate, and duration increased by adding epinephrine 4.
Chloroprocaine is a short-acting ester-type local anesthetic with rapid onset block for epidural administration 4.
Opioids
Fentanyl is a lipophilic short-acting opioid administered via epidural route 4. When added to continuous epidural infusions of local anesthetic, opioids reduce the concentration of local anesthetic needed, improve analgesia quality, and minimize motor block 5.
Morphine is a hydrophilic long-acting opioid that can be administered epidurally 4.
Adjuvant Medications
Dexmedetomidine is a selective alpha-2 adrenergic agonist providing analgesic, sedative, anxiolytic, and anti-shivering effects via epidural administration 4, 6. It is the highest-ranked pharmacologic agent for preventing intra- and postoperative shivering during cesarean delivery based on Level I evidence from 20 RCTs 6.
Clonidine is an alpha-2 adrenergic agonist used for analgesic, anxiolytic, and anti-shivering effects via epidural route 4.
Technical Equipment
The epidural technique requires:
- Epidural catheter for continuous infusion or intermittent bolus administration 5
- Pencil-point spinal needles (when combined spinal-epidural technique is used) to minimize postdural puncture headache risk 5
- Equipment and facilities comparable to those in the main operating suite, with resources for treating potential complications including failed intubation, inadequate analgesia/anesthesia, hypotension, respiratory depression, local anesthetic systemic toxicity, pruritus, and vomiting 5
Administration Techniques
Continuous epidural infusion uses dilute concentrations of local anesthetics with opioids to produce minimal motor block while maintaining effective analgesia 5.
Combined spinal-epidural (CSE) allows intrathecal administration of medication (usually local anesthetic with opioids) followed by epidural catheter placement for intraoperative and postoperative use 4.
Dural puncture epidural (DPE) is similar to CSE but without intrathecal medication administration, with only epidural catheter placement 4.