Transcript Anatomy of spinal anesthesia mgmc

Anatomy of spinal
anesthesia
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu), Dip. Diab.
DCA, Dip. Software statisticsPhD ( physiology)
Vertebrae
• Thirty-three vertebrae in the body cervical, thoracic,
lumbar, sacral and coccygeal. seven Presacral :
• cervical, - C 7
• twelve thoracic – T12
C7,
T12
• five lumbar vertebrae L5
L5
• Fibro cartilaginous intervertebral
S5
Co4
discs separate them.
• The five sacral (S 5)and
• four coccygeal vertebrae (Co4) are composite in
nature and they form sacral and coccygeal bone
respectively.
Adult vertebral column has four curvatures
• the thoracic and sacrococcygeal curvatures are
convex posteriorly and are called primary
curvatures.
• the cervical and lumbar curvatures are convex
anteriorly
and
they
are
secondary
or
compensatory curvatures that develop after
birth,
Lordosis and kyphosis
Vertebra – individual differences
– but
• Anterior body
• Posterior arch
Pedicle(superior and inferior notch),
lamina , (facets and transverse process)
Two lamina – spine
All are paired except spine !!
Pedicle, lamina ,spinous process
junction of lamina and pedicle – articular facets
• Between the body
and the arch is the
vertebral foramen
• Foramen continues
with each vertebra
down for the vertebral
canal
• Spinal cord and
meninges are safe
inside the canal
Vertebral canal
Width
• Cervical – 25
• Thoracic – 17
• Lumbar – 22 to 27
The AP dia is 15 – 17 mm
Superior and inferior notch –
foramen for exit of the nerve
The intervertebral foramen
contains
(a) both the ends of the anterior and posterior
nerve root with dorsal root ganglia,
(b) the beginning of mixed spinal nerve, (c) the
beginning of two rami of spinal nerve –anterior
and posterior,
(d) a spinal artery,
(e) an intervertebral vein.
Cord anatomy
• Cord ends at mid or lower end of L 1
• Dura continues to end at S2 – the CSF
• Bunch of nerves – cauda equina
• Expansion of subarachnoid space – lumbar
cistern – injection of intrathecal local anesthetics
• Pial remnant – filum terminale
Spine is straight
Median approach
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Skin
Subcutaneous tissue
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Dura
Arachnoid
CSF
Paramedian approach
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Skin
Subcutaneous tissue
Lumbar aponeurosis
Paravertebral muscles
Ligamentum flavum
Epidural space
Dura
Arachnoid
CSF
Lig. flavum may be having gap
in the midline – the “ gives”
• The space between the laminae of two
adjacent vertebrae and the interarticular
joint is called the interlaminar foramen
• Narrow in extended position
• That’s why we flex !!
interlaminar and Interspinous
but below the cord level
Taylor’s approach
Surface anatomy
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C7 - vertebra prominens
T3 - spine of scapula
T7 – inferior angle of scapula
Highest point of iliac crest – L4 – tuffier s
line
• Posterior superior iliac spine – S2
• Highly variable -- tuffier s line and L4L5
interspace
Possible ?? !!
• 14 % may have two
nerves in single
foramen
• When we plan
segmental neurolysis
• Think of this anomaly
• The most dependent points are T5 and S2
Spinal cord
• The spinal cord as a part of CNS is a continuation of
brain.- medulla – Ends as conus medullaris.
• The length of a spinal cord is 42 to 45 cm in an adult.
• Rarely goes to L 2-3.
• The spinal cord has two enlargements cervical and
lumbar, corresponding to the increased nerve supply
to the upper and lower limbs
• Spinal segment = vertebral level in fetus
• But at the time of birth, cord grows less
fast – L3
• Adult – L1
• So what happens –
• After lumbar segments – bunch of nerves
– cauda equina ..
• Segments don’t correspond !!
• The spinal cord is mainly supplied by two
• posterior and one anterior spinal arteries.
• Posterior – Posterior inferior cerebellar
arteries – reinforcement ++++
• But anterior descending – a twig from both
vertebral arteries – only at T11 –
adamkiewieze
No connection
between posterior and anterior
• The normal intraspinal capillary pressure
is 30 mm of Hg. Deprivation of blood
supply for 2 minutes may result in
infarction of cord
• Vertebral and azygous veins
31 pairs of
spinal nerves
--33 vertebrae
31 pairs
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8 cervicals,
12 thoracic,
5 lumbar,
5 sacral
1 coccygeal
The length of the spinal
cord, giving origin to the
rootlets for one spinal
nerve constitutes one
spinal segment.
So, the spinal cord is
made up of thirty one
such segments:
• Rootlets – dorsal and ventral roots
• Spinal nerve
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• Anterior and posterior primary rami
D
R
P
P
R
D
R
G
V
R
D
u
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a
l
c
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f
A
P
R
Rootlets , roots, nerve and rami
• 5000 neurons in anterior root The small diameter of
the anterior sacral roots is a risk factor in their
damage during technique
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Cervical 1 and coccygeal 1
– can have no dorsal roots
1 lakh in dorsal root
dorsal root is packed in loose bundles
So accessible more easy for local anesthetics
See-- sensory root is more easily attacked by local
anesthetics
CSF and the site of action of SA
• Spinal CSF volume is decreased in
pregnancy,obesity and increased intra
abdominal pressure ??
• Dose ??
• During cough , there is cranial movement of
spinal CSF ??
• Level – beware
• After radiological examination with contrast, the
unequal distribution of CSF in 45–84% of the
population has been observed.
So don’t worry about
segmental , patch
blocks – we may not be
the reason
How CSF ??
• CSF is a clear fluid that fills the subarachnoid space. pH – 7.4
•
total volume of CSF in the adult varies between 100-150 ml.
• CSF within the spinal subarachnoid space is 50 – 75 ml approx
• Cerebral spinal fluid is continually produced at a rate of 450
ml per day by the choroid plexuses, which are located in the
lateral. 3rd, and 4th ventricles.
• Cerebral spinal fluid is reabsorbed into the bloodstream
through the arachnoid villi and granulations and to a small
extent through epidural veins.
• Normal pressure – 100-180 mm water
• Upright – 370 -500 mm water
• Further increase during epidural injection
may cause dizziness
After Dural puncture –
Albumin rises
rate of production rises
many times
Specific gravity
• CSF = 1.0001 to 1.000028
• Density = mass/volume
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alcohol = 1030 kg/m3
Specific gravity
Density / density of water
Baricity
Density / density of the other solution
(CSF)
We are talking in terms of
baricity because –
CSF and bupivacaine
• Duramater – large collagen fibres with a
maximal interspace
• Thick but let fluids go easily
• Arachnoid – ( actually thin ) overlapping
flattened epithelial cells with tight junctions –
more resistance
Subdural !!
• potential space between the dura mater and the
arachnoid, the subdural space, that contains only small
amounts of serous fluid.
• not intentionally given
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injection into it during spinal anesthesia may explain the
occasional failed spinal anesthetic
• and the rare “total spinal” after pucca epidural anesthesia
Ankle ??
• S1 root is usually very thick
• May be upto 7.7 mm
• Resistance and delayed action
Sono anatomy
• Nothing is complete without
USG in anesthesia !!
• Obese , pregnant,
kyphoscoliosis
• Previous laminectomy
• Depth of space
• Direction of needle
• Find out the interspinous and
interlaminar space
Sono anatomy
PD = posterior dura
SC = spinal canal
AD = anterior dura
VB = vertebral body
USG
• The real time ultrasound guidance for
needle visualization and performance of
central neuraxial blockade is a three hand
technique needing two individuals
• USG guided spinal
• In the next decades – this will be a normal
phenomenon
Summary
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Vertebrae – number
Body , arch and foraminae
Spinal nerves – number
Differential growth and positioning
Roots , anterior posterior , thickness
CSF
Baricity
Sonoanatomy
Thank you all