Shiraz Yazdani and Salahadin Abdi

Neuraxial drug administration describes a method of delivering pharmacologic therapies directly to and around the spinal cord and nerve roots. This is commonly used in the field of anesthesiology as the primary or adjuvant anesthetic for patients undergoing surgery. In the field of pain medicine, medications are commonly delivered into the epidural or intrathecal space for the treatment of chronic pain. As many common causes of chronic pain can be traced to spinal nerve roots, targeted delivery of medications to these areas can be a valuable tool in the management of chronic pain.

Using epiduroscopy, these medications can be directed at structures suspected to be pain generators by visualization of pathology, contact diagnosis, or diagnostic/therapeutic injection. The epiduroscope can also be used as an aid in percutaneous catheter placement for continuous/intermittent infusion of medications to pain-generating structures. What follows is the most commonly used local anesthetics, steroids, and other agents.

• Hydrophilic.

• Low protein binding.

• Fast onset of action.

• Medium duration.

• Higher relative risk of transient neurologic symptoms than other local anesthetics.

• High protein binding.

• Medium onset of action.

• Long duration of action.

• Racemic mixture:

R-enantiomer is more likely to cause central nervous system toxicity and cardiotoxicity.

• High protein binding.

• Medium onset of action.

• Long duration of action.

• Less proconvulsant and arrhythmogenic than equivalent doses of bupivacaine.

• Alpha-2 agonist.

• Effective as an analgesic intrathecally.

• Used as an adjuvant to local anesthetics and opioids in the epidural space:

Reduces concentration of local anesthetic required for sensory blockade.

Increases degree of motor blockade caused by local anesthetics.

• May cause hypotension, bradycardia, and sedation.

• N-methyl-D-aspartate receptor antagonist.

• Use in neuraxial analgesia remains under investigation.

• Potentially neurotoxic if not used in a preservative-free solution.

• Cause analgesia via regional spinal cord receptors, cerebral receptors, and peripheral/central effects due to vascular absorption.

• Lipophilic opioids (e.g., fentanyl) have a rapid onset but short duration:

Narrower segmental analgesia.

• Hydrophilic opioids (e.g., morphine) have a slow onset but longer duration:

Wider segmental analgesia.