Transcript Spinal - GasLog

Anatomy of the spine
Blood supply of the spinal cord
Epidural & subarachnoid block
By
C. Quantock
BONY STRUCTURE
• The structure of the spine provides
stability, protection of the spinal cord, and
weight-bearing movement in the upright
posture.
BONY STRUCTURE
• A line drawn between both iliac crests
usually passes between the spinous
processes of L4 and L5.
• In slender individuals, the sacrum is
palpable and the sacral hiatus is felt as a
diamond-shaped or irregular depression
just above or between the gluteal clefts
BONY STRUCTURE
• The vertebrae are 33 in numberfive regions
–
–
–
–
–
cervical
Thoracic
Lumbar
Sacral
coccygeal.
• Double "C" curve has practical significance
when predicting the effects of gravity or patient
position on the movement of spinal anesthetic
solutions
BONY STRUCTURE
• A typical vertebra has structurally similar parts.
• Base of the vertebra is the vertebral body.
• Adjacent vertebral bodies are held together over
the intervening intervertebral disk by strong,
fibrous anterior and posterior longitudinal
ligaments - maintain the ventral stability of the
spine.
• A bony and ligamentous network forms the
spinal canal and maintains dorsal stability.
BONY STRUCTURE
• Attached directly to the vertebral body dorsally
are the paired pedicles - join with the laminae.
• Laminae meet and fuse in the midline
• The oval space created by the pedicles and
laminae forms the vertebral foramen.
• The confluence of adjacent vertebral foramina
creates the spinal canal
– spinal cord
– its coverings
– vascular supply.
BONY STRUCTURE
• Each pedicle is notched -creates
intervertebral foramen, through which
exits the corresponding spinal nerve.
• Spinous process provides for
ligamentous insertions that contribute to
posterior stability.
BONY STRUCTURE
• The most posterior and superficial
ligament is the supraspinous ligament
• Next is the interspinous ligament
• Deepest is the ligamentum flavum (joins
adjacent laminae) and is the immediate
covering over the dura mater.
• Potential space between ligamentum
flavum and dura mater is the epidural
space
BONY STRUCTURE
• Between the dura and arachnoid
membrane is another potential space, the
subdural space.
• the spinal subdural space is confluent with
the cranial subdural space.
• Unlike the epidural space, which ends at
the foramen magnum.
Regional differences in vertebral
structure
• In the cervical region
– The vertebrae have a foramen within their
transverse processes for passage of the
vertebral artery.
– the spinal canal is the widest and the
vertebral body the smallest of all spinal
regions.
– The spinous process is roughly horizontal.
• The thoracic vertebrae
– identified by their rib articulations on the
transverse process.
– Spinous processes are oblique and overlap.
• The lumbar vertebrae
– bodies are the largest in the spinal column
– nearly horizontal spinous processes.
• The five sacral vertebrae
– more or less fused into the sacrum.
– dorsal and ventral foramina for nerve exit
– defect in the roof on the dorsal aspect at the
caudal end - the sacral hiatus.
• The coccyx represents fusion of three or
four rudimentary vertebrae.
APPLIED ANATOMY OF THE
EPIDURAL SPACE
• The epidural space is bounded by
– the dura ventrally
– the ligamentum flavum dorsally.
• It extends from the foramen magnum to
the sacral hiatus.
• This space is filled with
– loose connective tissue
– epidural veins
– spinal nerve roots.
• The epidural venous plexus
– concentrated in a ventral and lateral location
– sparse in the midline.
• The veins communicate
– superiorly with intracranial venous sinuses
– inferiorly with the sacraL plexus
– ventrally with the thoracic and abdominal venae
cavae and the azygos system.
• The best way to avoid bleeding or placement of
needles and catheters directly into veins in the
epidural space is to stay as close to the midline
as possible on entry into the epidural space.
THE SPINAL CORD
• lies within the spinal canal.
• dura mater, fatty tissues, and a venous plexus,
are referred to as the meninges
• The outermost area is the epidural space, with
its veins and fatty connective tissue.
• The next layer is the dura mater, is confluent
with the intracranial dura,
• Extends distally as far as S2 in adults and
farther in children.
• Spinal nerves exit from intervertebral foramen at
the level of the corresponding vertebral body
• Spinal cord is shorter than the spinal column
• as the spinal segments progress caudally,
increasing distance that each nerve must travel
to its intervertebral foramen.
• Below L1, the spinal cord is usually not a single,
solid structure but has split into terminal
branches cauda equina ("horse's tail").
• Lumbar puncture is most often performed below
L1
BLOOD SUPPLY
• The spinal cord receives the majority of its blood
supply from two distinct sources:
– the anterior spinal artery
– the posterior spinal arteries
• paired posterior arteries
– rich collateral flow (arterial injury is an unlikely cause
of ischaemia)
– supply the posterior white and gray matter of the cord.
• The chief origin is the cerebral arterial system,
with collateral contributions from the
– subclavian, intercostal, lumbar and sacral arteries.
• Single midline anterior spinal artery
• supplies the ventral cord
• receives contributions from branches of
the
– vertebral artery and multiple segmental
branches from the cervical, thoracic
(intercostal arteries), and lumbosacral
• The posterolateral spinal arteries, branches of
the vertebral artery, only extend down to the
upper thoracic segments.
• A single segmental branch of the aorta (artery
of Adamkiewicz) supplies nearly all of the flow
to the lower thoracic and lumbar segments.
• Injury to this artery renders this entire segment
of cord at risk for ischemia.
• The artery Adamkiewicz is typically unilateral
(statistically most often the left side.)
PHYSIOLOGY
• The physiologic response is determined by
the effects of interrupting the afferent and
efferent innervation of somatic and
visceral structures.
• Somatic structures are traditionally related
with sensory and motor innervation
• Visceral structures are more related to the
autonomic nervous system.
PHYSIOLOGY
SOMATIC BLOCKADE
• Prevention of pain and skeletal muscle
relaxation are the classic objectives of
central blockade.
• A local anesthetic is injected into the
subarachnoid space.
• It mixes with cerebrospinal fluid and is
exposed to the spinal cord.
• Spread occurs as a result of a number of factors
–
–
–
–
including gravity
cerebrospinal fluid pressure
patient position
solution temperature.
• The local anesthetic becomes less concentrated
as it mixes with cerebrospinal fluid.
• Neural blockade occurs at a certain minimum
(threshold) concentration referred to as Cm.
• But nerve fibers are not homogeneous.
• There are three main fiber types, designated A,
B, and C.
– A group has four subgroups: alpha, beta, gamma, and
delta.
• the onset of central anesthesia is not uniform,
Cm varies depending upon fiber type
– fibers are blocked more easily if they are small and
myelinated
– less easily if they are large and unmyelinated.
Class
Action
Myelin
Size
C,,
Aα
M o to r
Yes
++++
++++
Aβ
Light to uch,
pressure, pain
Yes
+++
++
Aγ
M uscle spindles
Yes
+++
++
Aδ
P ain,
temperature
Yes
++
+
B
P reganglio nic
sympathetic
Yes
++
+
C
P ain, pressure
No
+
+++
• As diffusion and dilution of the injected agent
occurs, the more resistant fibers may not be
completely blocked
• The result is that
– sympathetic blockade (judged by temperature
sensitivity) may be two segments higher than
– the sensory block (pain, light touch), which in turn is
– two segments higher than motor blockade.
• Segments where one mode is blocked and
another not blocked are referred to as zones of
differential blockade.
• When evaluating the level of a block, it is
important to keep in mind which modality
is being assessed
– temperature (sympathetic),
– pin prick (sensory),
– movement (motor)
• the maximum level will be different for
each.
VISCERAL BLOCKADE
Cardiovascular
• The sympathetic chain originates from the
lumbar and thoracic spinal cord.
• T1-4: cardiac accelerator fibers
• T5 to L1: fibers involved in smooth muscle
tone of the arterial and venous circulation
• Sympathetic denervation results in cardiovascular
changes of hemodynamic consequence in proportion to
the degree of sympathectomy.
– Partial sympathectomy (T8 block) usually allows physiologic
compensation with vasoconstriction, mediated by sympathetic
system fibers above the level of the block.
– Total sympathectomy results is an increase in the volume of the
capacitance vessels, a subsequent decrease in venous return to
the heart, and hypotension.
– When blocked by high central blockade, unopposed vagal
activity leads to bradycardia.
Pulmonary
• Tidal volume, minute ventilation, and maximum
inspiratory volume usually maintained by the
diaphragm.
• Maximum breathing capacity and active
exhalation are impaired in proportion to the loss
of abdominal and intercostal muscle motion.
• This will affect the patient COPD who is
dependent on accessory muscles to actively
exhale.
• To retain the advantages of regional anesthesia
in pulmonary patients the motor block should be
kept below T7.
FACTORS INFLUENCING
SPINAL ANESTHESIA
• Local anesthetic action at the spinal
nerves and the dorsal ganglia accounts for
spinal anesthesia
• concentration found within the substance
of the spinal cord too low to have any
clinical effect.
• Agent
– Procaine,Tetracaine,Lignocaine,
Bupivacaine
• Dosage
Proper dose is determined considering
– the properties of the agent
– type of surgical procedure
– anticipated duration of surgery.
• Other patient factors affecting dose
include
– obesity, pregnancy, age, and positioning
during surgery.
• Obesity/pregnancy
– increases intra-abdominal pressure
– engorgement of the epidural venous plexus
– causing a decrease in the volume of cerebrospinal
fluid and epidural space
– increase in level of the spinal anesthesia.
• Age
– The volume of the subarachnoid space and epidural
space becomes lower with aging
– more cephalad spread with advancing age.
Specific Gravity
• Specific gravity is cerebrospinal fluid 1.0031.008 at 37 °C.
• The relationship of the specific gravity of LA to
that of CSF affects the solution's migration.
– Hypobaric:solution is lighter – will float up
– Isobaric: specific gravity identical it will stay at about
the same level where it is injected
– Hyperbaric: solution has greater specific gravity - it
will gravitate down
Agent
Procaine
1.5% in water
2.5% in DgVV
Lidocaine :
2% plain
5% in 7.5% dextrose
Tetracaine, 0.5% in D5W
Bupivacaine
0.5% in 8.25% dextrose
0.5% in water
Specific
Gravity
1.0052
1.0203
1.0066
1.0333
1.0203
1.0278
1.0058
Specific1.0058
Agent
1.0052
1.0066
Tetracaine,
1.0278
1.0203
1.0203
1.0333
Gravity
0.5% in DgW
Posture
• The position of the patient
– during injection of local anesthetic
– before final binding of the agent to central
nervous system tissues
• influences the eventual level of the drug.
• With the patient in the sitting position,
hyperbaric solutions will migrate in a
caudad manner and hypobaric solutions in
a cephalad manner.
Intra-abdominal Pressure
• Indirect effect on the final level of injected
local anesthetic by changes in
– the contour of the subdural space
– the total volume of the cerebrospinal fluid
Spinal Curvature
• Abnormal curvatures of the spine—specifically, scoliosis
and kyphoscoliosis—have multiple effects on spinal
anesthesia.
• Placing the block becomes more difficult
• Finding the midline and the interlaminar space can be
difficult
• Spinal curvature affects the ultimate level by changing
the contour of the subarachnoid space.
• Severe kyphosis can be associated with a decreased
volume of CSF
Prior Spinal Surgery
• Associated with technical difficulties in
placing the block
• Alterations in the final level of the block
may be related to changes in the contour
of the subarachnoid space
COMPLICATIONS
• Pain on Injection
– experienced by many patients
• Backache
– Needle penetration can cause:
• hypaeremia,
• local tissue irritation,
• reflex spasm of muscles.
• typically passes in 10-14 days
.
Spinal headache
• related to persistence of the dural
puncture,
• leakage of cerebrospinal fluid
• chronic lowering of cerebrospinal fluid
pressure.
• This exerts downward traction on the
structures of the CNS.
• The result is a headache similar to acute
vascular cluster headache.
Spinal headache
•
•
•
•
•
The headache is
postural in nature,
typically beginning within 6-12 hours
worse in the upright position.
Throbbing frontal quality, association with
nausea and vomiting
• Prompt relief upon resumption of the
supine position.
Spinal headache
• The most important factor associated with PDPH
is needle size
• more common and more severe as needle size
increases.
• fibers of the dura are arranged in a longitudinal
manner,
• pencil-point needles split the fibres, not cutting
them.
• Another factor
• age and sex (older and male having less risk).
• In pregnancy more common.
Spinal headache
• Conservative treatment
• aggressive hydration, soft diet, stool softeners,
abdominal binders, and oral analgesics.
• If headache persists: epidural blood patch.
• Epidural needle into the interspace where the lumbar
puncture was performed.
• Fifteen mL of the patient's blood until
– 15 rnL has been injected
– the patient experiences pressure in the ears.
• 95% of patients have complete relief after the first patch
when done 24 hours or more after dural puncture.
• Second attempt success rate approaching 99%.
Urinary retention
• Blockade of S2-4 is associated with loss of
bladder tone and inhibition of the voiding
reflex.
• Overfilling of the bladder can occur, and
even after resolution of the blockade
voiding may be difficult.
• Especially common in male patients
• Bladder distention can be associated with
– hemodynamic alteration - hypertension and
– agitation
Meningitis
• Chemical (aseptic) meningitis causes
transverse myelitis and spinal cord gross
dysfunction below the level where it
occurs.
• This has been associated with the use of
reusable spinal needles that were cleaned
in caustic substances.
• Is possibility of infectious meningitis
Vascular Injury
• Injury to blood vessels can be associated
with serious complications, including
epidural hematoma.
• Most commonly in patients
– with coagulopathy
– who have been taking anticoagulants
– in patients with no apparent risk factors.
• Any spinal anesthetic that does not resolve
within a reasonable period or that suddenly
progresses after initial resolution of
symptoms should suggest possible epidural
hematoma
Nerve Injury
• Incidence of postoperative nerve injury is
thought to be less than 1:10,000.
• The nerve injuries that do occur tend to
consist of persistent paresthesias that
resolve without treatment within weeks or
months.
• Prevention depends upon detection of
paresthesia during needle placement.
High Spinal Anesthesia
• With high thoracic or cervical levels, severe
hypotension, profound bradycardia, and respiratory
insufficiency become likely.
• If profound hypotension persists, hypoperfusion of
the medullary respiratory center will lead to apnoea.
• Treatment: support of the airway and circulation.
• Decreases in heart rate and blood pressure are
expected.
• Hypotension: rapid administration of intravenous
fluid use of vasopressors – ephedrine/phenylephrine
• Bradycardia: anticholinergic (atropine)