Spinal & Epidural Neuraxial Anesthesia

Comprehensive vocabulary regarding central neuraxial anesthesia, including anatomy, pharmacology, physiology, and complications.

Neuraxial Anesthesia

A form of regional anesthesia involving the central nervous system, specifically spinal or epidural blocks.

Anterior Segment of Vertebra

The part of the vertebra known as the body.

Posterior Segment of Vertebra

The part of the vertebra known as the vertebral arch.

Vertebral Foramen

The space formed by the connection of the lamina and pedicle that houses the spinal cord, nerve roots, and epidural space.

Aortic Stenosis

A major contraindication for spinal anesthesia due to the risk of sympathectomy and inadequate heart function to maintain blood pressure.

Tuffier's Line

A landmark for spinal or epidural placement, usually located at the level of the $L4$ spinous process or the $L3-L4$ interspace.

Conus Medullaris

The lower end of the spinal cord, which typically terminates at the level of $L1$ in adults and $L3$ in infants.

Cauda Equina

A bundle of spinal nerves and nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve.

Dermatome

An area of skin supplied by a single spinal nerve root; used to assess sensory levels of a block.

T4 Dermatome

The sensory level corresponding to the level of the nipples.

T10 Dermatome

The sensory level corresponding to the level of the umbilicus.

B Fibers

Small, myelinated preganglionic autonomic nervous system (ANS) fibers that are usually the first to be blocked during neuraxial anesthesia.

C Fibers

Small, unmyelinated fibers responsible for slow pain, temperature, and touch; they are among the second group of fibers to be blocked.

A-alpha Fibers

Heavy, myelinated fibers responsible for skeletal muscle motor function and proprioception; they are the last to be blocked and the first to recover.

Bezold-Jarisch Reflex

A reflex characterized by the triad of bradycardia, hypotension, and cardiovascular collapse, which can be triggered by decreased venous return during neuraxial anesthesia.

pKa (Pharmacology)

The pH at which $50\%$ of a local anesthetic is non-ionized; compounds with a pKa closer to physiologic pH ($7.4$) generally have a faster onset.

Hyperbaric Solution

A local anesthetic solution with a density greater than CSF, causing it to sink to the dependent parts of the subarachnoid space.

Hypobaric Solution

A local anesthetic solution with a density less than CSF, causing it to float upward in the subarachnoid space.

Epidural Space

A potential space outside the dura mater containing fat, veins, and nerve roots; it requires much larger volumes of local anesthetic than the spinal space.

Postdural Puncture Headache (PDPH)

A headache, often frontal and light-sensitive, caused by CSF leakage following a dural puncture; it typically worsens with sitting or standing.

Epidural Blood Patch (EBP)

The injection of autologous sterile blood into the epidural space to seal a dural puncture and relieve a postdural puncture headache.

Local Anesthetic Systemic Toxicity (LAST)

A life-threatening systemic complication from the inadvertent intravascular injection of local anesthetics, most commonly associated with Bupivacaine.

Lipid Emulsion $20\%$

The standard treatment or antidote for Local Anesthetic Systemic Toxicity (LAST).

Transient Neurological Symptoms (TNS)

Temporary pain or sensory changes in the lower extremities following spinal anesthesia, historically associated with the use of $5\%$ Lidocaine.

Tuohy Needle

A blunt-tipped epidural needle with a $30$-degree curve intended to help guide the catheter into the epidural space and prevent dural puncture.

Pencil-point Needle

A non-cutting spinal needle (e.g., Sprotte or Whitacre) associated with a significantly lower risk of postdural puncture headache compared to cutting needles.

Epidural Test Dose

A small dose of local anesthetic (usually $3\,ml$ of $1.5\%$ Lidocaine with Epinephrine $1:200,000$) used to detect if a catheter is in a vein or the subarachnoid space.

Co-loading

The practice of rapidly administering intravenous fluids at the same time the neuraxial block is initiated to prevent hypotension.

ASRA (American Society of Regional Anesthesia)

The organization that provides evidence-based guidelines for managing neuraxial anesthesia in patients on anticoagulants.

Ligamentum Flavum

The tough, yellowish ligament that is the last layer pierced before the needle enters the epidural space, often characterized by a 'pop' or loss of resistance.