ANESTHESIOLOGY MIDTERM II

SPINAL and EPIDURAL ANESTHESIA

ANATOMY
The vertebral column consists of 33 vertebrae:
- 7 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 4 coccygeal

In the embryonic period, the spine curves into a C shape, forming two primary curvatures with
their convex aspect directed posteriorly. These curvatures persist through adulthood as the
thoracic and sacral curves. The cervical and lumbar lordoses are secondary curvatures that develop
after birth as a result of extension of the head and lower limbs when standing erect. The
secondary curvatures are convex anteriorly and augment the flexibility of the spine.

Atypical cervical vertebrae:

C1 – atlas ; ringlike bone that has no body or spinous process
C2 – axis ; has an odontoid process that protrudes superiorly
C7 -- vertebra prominens; has a long, nonbifid spinous process that serves as a useful landmark
for a variety of regional anesthesia procedures.

Vertebral facet (zygapophyseal) joints - articulate posterior elements of adjacent vertebrae.

The junction of the lamina and pedicles gives rise to inferior and superior articular processes.

Five sacral vertebrae fuse to form the wedge-shaped sacrum, which connects the spine with the
iliac wings of the pelvis. In childhood, the sacral vertebrae are connected by cartilage, which
progresses to osseous fusion after puberty, with only a narrow remnant of sacral disk remaining in
adulthood. Fusion is generally complete through the S5 level, although there can be complete lack
of any posterior bony roof over the sacral vertebral canal.

Sacral hiatus - an opening formed by the incomplete posterior fusion of the fifth sacral vertebra.
It lies at the apex of the coccyx, which is formed by the union of the last four vertebrae.

Significance: This hiatus provides a convenient access to the caudal ending of the epidural
space, especially in children. The sacral cornu are bony prominences on each side of the
hiatus that are easily palpated in small children and serve as landmarks for a caudal
epidural block.
Intervertebral Ligaments
Anterior and posterior longitudinal ligaments - run along the anterior and posterior surfaces of
the vertebral bodies, respectively, reinforcing the vertebral column.

Supraspinous ligament - a heavy band that runs along the tips of the spinous processes,
becomes thinner in the lumbar region. This ligament continues as the ligamentum nuchae
above T7 and attaches to the occipital external protuberance at the base of the skull.

Interspinous ligament - is a narrow web of tissue that attaches between spinous processes;
anteriorly it fuses with the ligamentum flavum and posteriorly with the supraspinous ligament

Ligamentum flavum- a dense, homogenous structure, composed mostly of elastin which

connects the lamina of adjacent vertebrae. The lateral edges of the ligamentum flavum
surround facet joints anteriorly, reinforcing their joint capsule.

Significance: When a needle is advanced towards the epidural space, there is an easily
perceptible increase in resistance when the ligamentum flavum is encountered. More
importantly for the practice of neuraxial anesthesia, a perceptible, sudden loss of resistance
is encountered when the tip of the needle passes through the ligamentum and enters the
epidural space.

Spinal Meninges and Spaces

The spinal cord is an extension of the medulla oblongata. It has three covering membranes: the
dura, arachnoid, and pia maters. These membranes concentrically divide the vertebral canal into
three distinct compartments: the epidural, subdural, and subarachnoid spaces.

Epidural space - contains fat, epidural veins, spinal nerve roots, and connective tissue

Subdural space - a “potential” space between the dura and the arachnoid and contains a serous
fluid. The subdural compartment is formed by flat neuroepithelial cells that have long interlacing
branches.

Subarachnoid space - traversed by threads of connective tissue extending from the arachnoid
mater to the pia mater. It contains the spinal cord, dorsal and ventral nerve roots, and
cerebrospinal fluid (CSF). The subarachnoid space ends at the S2 vertebral level.
Spinal Cord

There are 8 cervical neural segments. The eighth segmental nerve emerges between the seventh
cervical and first thoracic vertebrae, whereas the remaining cervical nerves emerge above their
same-numbered vertebrae. Thoracic, lumbar, and sacral nerves emerge from the vertebral column
below the same- numbered bony segment. Anterior and posterior spinal nerve roots arise from
rootlets along the spinal cord. The roots of the upper and lower extremity plexuses (brachial and
lumbosacral) are significantly larger compared to other levels.

The dural sac is continuous from the foramen magnum to the sacral region, where it spreads
distally to cover the filum terminale.

In children, the dural sac terminates lower, and in some adults, the sac termination can be as high
as L5. The vertebral canal contains the dural sac, which adheres superiorly to the foramen
magnum, to the posterior longitudinal ligament anteriorly, the ligamentum flavum and laminae
posteriorly, and the pedicles laterally.

The spinal cord tapers and ends as the conus medullaris at the level of the L1–L2 intervertebral
disk. The filum terminale, a fibrous extension of the spinal cord, extends caudally to the coccyx.
The cauda equina is a bundle of nerve roots in the subarachnoid space distal to the conus
medullaris.

Spinal anesthesia involves the use of small amounts of local anesthetic injected into the
subarachnoid space to produce a reversible loss of sensation and motor function. Local anesthetics
administered in the subarachnoid space block sensory, autonomic, and motor impulses as the
anterior and posterior nerve roots pass through the CSF. The site of action includes the spinal
nerve roots and dorsal root ganglion.

Epidural anesthesia involves the absorption of local anesthetic, systemically by the rich venous
plexus found within the epidural space. Dura surrounding spinal nerve/nerve roots are a modest
barrier to the spread of local anesthetics. A small amount of local anesthetic will be absorbed into
epidural fat. What remains will eventually reach its intended site of action, the spinal nerve and
nerve roots.
 REGIONAL ANESTHESIA

PERIPHERAL NERVE BLOCKADE: BASIC ANATOMY

Nerves are bundles of nerve fibers that lie outside the central nervous system and serve to conduct
electrical impulses from one region of the body to another. All peripheral nerves are similar in structure.
Neuron - basic functional unit responsible for the conduction of nerve impulses
PARTS of a NEURON:
a. Cell body (soma) - contains a large nucleus
b. Dendrites - receive incoming messages
c. Axons - conduct outgoing messages

CONNECTIVE TISSUE
a. Epineurium – outermost layer that surrounds an entire nerve and holds it loosely to the
connective tissue through which it runs.
b. Perineurium – connective tissue that surrounds a fascicle (each group of axons that bundles
together
within a nerve
c. Endoneurium - fine connective tissue within a fascicle that surrounds every individual nerve
fiber or
axon.

There are 31 pairs of spinal nerves

Dermatome - area of the skin supplied by the dorsal (sensory) root of the spinal nerve
Myotome - segmental of skeletal muscle by a ventral root of a specific spinal nerve
Osteotome - innervation of the bones; it follows its own pattern and does not coincide with the
innervation of more superficial structures

NERVE PLEXUSES
A. CERVICAL PLEXUS
- Originates from the ventral rami of C1-C5
- Sensory innervation: part of the scalp, neck, and upper shoulder
- Motor innervation: muscles of the neck and thoracic cavityof the

SPINAL
NERVES DISTRIBUTION
SEGMENTS
Five of the extrinsic laryngeal
Ansa cervicalis (superior muscles (sternothyroid, sternohyoid,
C1-C4
and inferior branches) omohyoid, geniohyoid, and thyrohyoid) by
way of N XII
Lesser occipital,
transverse cervical,
supraclavicular, C2-C3 Skin of upper chest, shoulder, neck and ear
and greater auricular
nerves
Phrenic nerve C3-C5 Diaphragm
Cervical nerves C1-C5 Levator scapulae, scalene
 muscles, sternocleidomastoid, and trapezius
muscles (with N XI)

B. BRACHIAL PLEXUS
- Innervates the pectoral girdle and upper limb
- Formed by 5 roots that originate from the ventral rami of spinal nerves C5-T1
- Roots converge to form the superior (C5-C6), middle (C7), and inferior (C8-T1) trunks Trunks give
- off three anterior and three posterior divisions as they approach the clavicle Divisions rearrange
- their fibers to form the lateral, medial, and posterior cords
- Cords give off the terminal branches:
o Lateral cord gives off the musculocutaneous nerve, and the lateral root of the median nerve

o Medial cord gives off the medial root of the median nerve and the ulnar nerve
o Posterior cord gives off the axillary and radial nerves.

C. LUMBAR PLEXUS
- formed by the ventral rami of spinal nerves L1-L3 and the superior branch of L4.
 - Main branches of the lumbar plexus are the iliohypogastric, ilioinguinal, genitofemoral,
lateral femoral cutaneous, obturator, and femoral nerves
NERVE(S) SPINAL SEGMENTS DISTRIBUTION

Iliohypogastric Abdominal muscles (external and internal oblique

T12-L1 muscles, transverse abdominis muscles); skin over
nerve
inferior abdomen and buttocks
Abdominal muscles (with iliohypogastric nerve); skin
Ilioinguinal nerve Li over superior, medial thigh, and portions of external
genitalia

Genitofemoral Skin over anteromedial surface of thigh

L1, L2
nerve and portions over genitalia
Lateral
femoral cutaneous L2, L3 Skin over anterior, lateral, and posterior
nerve surfaces of thigh
Anterior muscles of thigh (sartorius muscle and
quadriceps group); adductor of thigh (pectineus and
Femoral nerve L2-L4 iliopsoas muscles); skin over anteromedial surface of
thigh, as well as the medial surface of leg, and foot
through the saphenous nerve

Adductors of thigh (adductors magnus, brevis, and

longus); gracilis muscle; skin over medial surface of
Obturator nerve L2-L4 thigh. Note: Writing about a branch of a branch of
the lumbar plexus may pro- duce some confusion.

D. SACRAL PLEXUS
- Arises from the lumbosacral trunk (L4-L5) plus the ventral rami of S1-S4
- Main nerves of the sacral plexus are the sciatic nerve and the pudendal nerve Sciatic
- nerve
o leaves the pelvis through the greater sciatic foramen to enter the gluteal area where
it travels between the greater trochanter and ischial tuberosity
o In the proximal thigh it lies behind the lesser trochanter of the femur covered
superficially by the long head of the biceps femoris muscle.
o As it approaches the popliteal fossa, the two components of the sciatic nerve diverge
into two recognizable nerves: the common peroneal and the tibial nerve

SPINAL
NERVE(S) DISTRIBUTION
SEGMENTS
Gluteal
nerves L4-S2 Abductors of thigh (gluteus minimus, gluteus medius, and
Superior tensor fasciae latae); extensor of thigh (gluteus
Inferior maximus)
Posterior
femoral S1-S3 Skin of perineum and posterior surface of thigh and leg
cutaneous
Two of the hamstrings. Note: All three hamstrings are
nerve
Sciatic nerve L4-S3 innervated by the sciatic nerve (only motor nerve of the
posterior thigh), especially the long head of
 biceps (semitendinosus and semimembranosus); adductor
magnus (with obturator nerve)
Flexor of knee and plantar flexors of ankle (popliteal,
gastrocnemius, soleus, and tibialis posterior muscles and long
Tibial nerve L4-S3 head triceps of biceps femoris mus- cle); flexors of toes; skin
over posterior surface of leg, plantar surface of foot

Biceps femoris muscle (short head); peroneus (brevis and

Common longus), and tibialis anterior muscles; extensors of toes, skin
L4-S3
peroneal over anterior surface of leg and dorsal surface of foot; skin
nerve over lateral portion of foot (through the sural nerve)
Muscles of perineum, including urogenital diaphragm and
external anal and urethral sphincter muscles; skin of external
Pudendal nerve S2-S4
genitalia and related skeletal muscles (bulbospongiosus,
ischiocavernosus muscles)

INNERVATION OF MAJOR JOINTS in the BODY

Shoulder Joint - axillary and suprascapular nerves, both of which can be blocked by an interscalene block

Elbow Joint - branches of all major nerves of the brachial plexus: musculocutaneous, radial,
median, and ulnar nerves.

Hip Joint - nerve to the rectus femoris from the femoral nerve, branches from the anterior division of
the obturator nerve, and the nerve to the quadratus femoris from the sacral plexus

Knee Joint - innervated anteriorly by branches from the femoral nerve. On its medial side it receives
branches from the posterior division of the obturator nerve while both divisions of the sciatic nerve supply its
posterior side

Ankle Joint - involves the terminal branches of the common peroneal (deep and superficial peroneal
nerves), tibial (posterior tibial nerve), and femoral nerves (saphenous nerve). A more simplistic view is that
the entire innervation of the ankle joint stems from the sciatic nerve, with the exception of the skin on the
medial aspect around the medial malleolus (saphenous nerve, a branch of the femoral nerve)

Wrist Joint – innervated by most of the terminal branches of the brachial plexus including the
radial, median, and ulnar nerves
BASIC BLOCKS

BLOCK INDICATIONS
INTERSCALENE nerve block Roots of the brachial plexus Shoulder surgery; clavicular
surgery
SUPRACLAVICULAR nerve block Divisions of the brachial plexus Surgery of the upper arm
INFRACLAVICULAR nerve block Cords of the brachial plexus Surgery of the elbow
and forearm
AXILLARY nerve block Branches of the brachial plexus Surgery of the elbow, forearm,
hand
WRIST block Terminal branches of the Surgery of the hand
brachial plexus (median, ulnar,
radial nerves)
FEMORAL nerve block Surgery of the hip, knee,
proximal femur
SCIATIC nerve block Surgery of the tibia/fibula/foot
ANKLE block Terminal branches of the Surgery of the foot
common peroneal, tibial and
femoral nerves

EQUIPMENT for PNB:

Nerve Stimulator
- The goal of nerve stimulation is to place the tip of the needle in close proximity to the target
nerve to inject the local anesthetic in the vicinity of the nerve.
- This method uses a low-intensity (up to 5 mA) and short-duration (0.05-1 ms) electrical
stimulus
1-2 (at
Hz repetition rate) to obtain a defined response (muscle twitch or sensation) to locate a
nerve or nerve plexus with an (insulated) needle.
peripheral

Ultrasound

- Ultrasound technology allows 1. visualization of the anatomic structures, 2. the approaching needle,
and the 3. spread of local anesthetic

Needles

- A wide array of needles is available for performing PNBs. Choice of needle depends on the block
being performed, the size of the patient, and preference of the clinician.
- Needles are typically classified according to tip design, length, gauge, and the presence or
absence of electrical insulation or other specialized treatment of the needles

Continuous catheters

- Allows continuous delivery of the local anesthetic to the area being blocked.