Spinal Anaesthesia - Anatomy & Physiology

Spinal AnaesthesiaApplied anatomy and

physiology

CHAIRPERSON:DR.S.B GANGADHAR MODERATOR :DR. PRAKASH

PRESENTOR: DR.DABER PAREED

INTRODUCTION

• Spine is one of the most important part of human body

• It gives structure and support

• Protect the spinal cord

• There are

• 7 cervical vertebra

• 12 thoracic vertebra

• 5 lumbar vertebra

• There are five sacral and four coccyx vertebra which are fused segments

PARTS OF THE VERTEBRA

• All vertebra consists of BODY anteriorly

• Two pedicles that project posteriorly

• Two lamella that connect the pedicles

• Lamella gives rise to the transverse process that project

laterally and spinous process that project posteriorly

`• The pedicles of these vertebra are notched and

these notches of the each adjacent pair form an

intervertebral foramen through which the spinal

nerves exit the vertebral canal

• Superior and inferior articular processes arise at

the junction of the lamella and the pedicles and

form joints with the adjoining vertebrae

LIGAMENTS • The vertebral bodies are stablized by ligaments that increase in size between the

cervical and lumbar vertebra.. They are

• Supraspinous ligament – stong, thick, fibrous band

from C7 to sacrum

Supraspinous continue as ligamentum nuchae from C7 and attach

to the occipital protruberence at the base of the skull

• Interspinous ligament - Thin , fibrous structure

Extend from the apex & upper surface of a lower spine toward the

root and inferior surface of the next higher vertebrae

• Ligamentum flavum

LIGAMENTUM FLAVUM

• The ligamentum flavum consists of yellow elastic tissue

• They extend in perpendicular direction between the

anterior inferior surface of the upper lamina downward

to the anterior superior surface of the lower lamina

• Thus the ligament exists as right and left half in each

intervertebral space with the halves fusing in the

midline

Ligamentum flavum

IN NORMAL ADULTSThickness- 3-5mmHeight- 15-16mmWidth- 16-20 mm

CERVICAL VERTEBRAE

• The 1st cervical vertebra (atlas)has no body

• It consists of an anterior and posterior arch

joined by the thick lateral mass.

• The superior articular facets are strongly

concave for articulation with the occipital

condyles.

CERVICAL VERTEBRAE

• The second cervical vertebrae also has similar articulating

surfaces

• The superior articulating facets are large oval and they face

upwards and outwards

• The inferior facets resemble that of a typical cervical

vertebrae

• They have a small transverse process and laminae are thick

and the spine is large strong and bifid

• The typical cervical vertebrae are C3–C6.

• Each of these has a small flattened body and a triangular,

relatively large vertebral foramen.

• The pedicles project laterally as well as backwards, and

their superior and inferior notches are about equal.

• The transverse process is short and is pierced by the

foramen transversarium which transmits the vertebral

vessels

CERVICAL VERTEBRAE

• The first vertebrae to be clearly palpable while running down the

finger through the nuchal furrow of the spine is C7.

• There are 8 cervical nerves

• All the nerves emerge from C1 to C7 that emerge above their

corresponding vertebrae

• C 8 lies above the first thoracic vertebrae and the remaining spinal

nerves emerge below their corresponding vertebrae.

Thoracic vertebrae

• The typical thoracic body is the conventional heart shaped

• The upper 2 bodies show a transition from the cervical type,

whereas the lower vertebrae show some similarity to the

lumbar bodies.

• The bodies of T5-T8 are flattened on their left side; this

asymmetry is produced by the pressure of the descending

aorta & it is these 4 vertebra that become eroded by an

aneurysm of this aortic segment.

• The vertebral foramen is circular, diameter relatively

small.

• The spines are long and T1 projects almost horizontally

backwards and is readily felt below the vertebra

prominens.

• It is necessary to give a markedly cephalad angulation to

pass between the spines since the spines of mid thoracic

vertebrae are angled caudally

Lumbar vertebrae

• Lumber vertebrae is large kidney shaped.

• Vertebral foramen is roughly triangular, larger than the

thoracic and smaller than the cervical region.

• The pedicles are thick and transverse process are slender

• They increase in length from Ll to L3,then becomes shorter

again so that the third transverse process is longest

SACRAL VERTEBRAE

• The sacrum conists of 5 fused vertebrae

• In childhood the sacral vertebrae are connected by

cartilage.

• But progressively fuse into single structure after puberty.

• In the adult only a narrow residue of the sacral discs

persists.

• The fusion of adjacent vertebrae eliminates the

intervertebral foramina.

• The sacral hiatus is triangular and obliquely

placed at the lower end of the sacrum

• It is formed as a result from the failure of fusion

of the laminae of the 5th sacral segment

• The epidural space terminates here and hence

forms a convinient portal of entry into this

compartment

EMBRYOLOGY

• Embryologically each vertebra develops from 3 primary ossification

centres two lateral for the arch and one central body

• Osific granules appear about the eight month of the embryonic life

where the tranverse processes laterally project

• They travel in 2 directions: backward to form lamina and by

meeting in the midline to form spinous process.

• Anteriorly to meet the body and to form pedicles

• In the early fetal life spinal cord is as long as that of the vertebral

column

• At 3 month of the fetal life the tip of the cord is present at the 2nd

coccygeal vertebra

• At 6 month of life it comes to the level of S5

• At birth the spinal cord is at the lower border of L3 vertebrae

• After 1 year of age it comes at the level of L2

DEVELOPMENT

Curvature of the spine

• Cervical curve - Convex anterior

• Thoracic curve - Convex posterior

• Lumbar curve - Convex anterior

• Sacrococcygeal – Convex posterior

VERTEBRAL ANAMOLIES

Kyphosis

Scoliosis

Spina bifida

Spina bifida occulta

Meningocoele

Myelomeningocoele

Myelocoele

Kyphosis

• Kyphosis is an exaggerated

anterior flexion of the spine

resulting in a rounded or

hunchback appearance.

• Scoliosis and kyphosis are

often seen together.

• More common in women,

scoliosis

• Scoliosis is a complex

deformity of the spine

resulting in lateral curvature

and rotation of the vertebrae

as well as deformity of the rib

cage.

• There is usually secondary

with involvement of

respiratory, cardiovascular and

neurological symptoms.

Spina bifida• Neural arch defects result from the failure of fusion of 2 arch

centers.

• Usually this is not associated with any neurological

abnormality(spina bifida occulta), although in such cases

there may be an overlying dimple, lipoma or tuft of hair to

warn the observant of a bony anomaly beneath.

• It may occur any where in the vertebral column but majority

of defects involve L5 or upper sacral regions

• Spina bifida occulta – failure

of vertebral arch fusion only.

Meninges and nervous tissue

are normal.

• Meningocele – protrusion of

meninges through a posterior

vertebral defect.

• Myelomeningocele – neural

tissue protrudes into, & may

be adherent to, the meningeal

sac.

• Myelocele ( rachischisis) –

failure of fusion of neural tube

results in the production of an

open spinal plate. This

condition is incompatible with

survival.

MENINGES• The spinal meninges consists of three protective

membranes which are continuous with the cranial

meninges.They are

Dura mater

Arachnoid mater

Pia mater

DURA MATER

• The outermost and thickest meningeal layer is the dura mater

• It is the continuation of the inner (meningeal) layer of the cerebral

dura which is made up of dense fibrous tissue

• It extends foramen magnum and ends at the level of S2 where it

fuses with the filum terminale

• The dura is thickest in the posterior midline and thinner in the

lumber area.

• It is largely acellular except for a layer that forms the border

between the dura and the arachnoid matter

Arachnoid

• It is a delicate avascular membrane which lies next to the dura

matter

• Thin membrane that encloses the subarachnoid space and CSF.

• It is continuous with the cerebral arachnoid, which loosely invests

the brain, and dips into the longitudinal fissure between the

cerebral hemispheres.

Piamater

• It is the innermost layer of the 3 membranes

• It is a vascular connective tissue sheath that closely

invests the brain & spinal cord, and projects into

their sulci and fissures.

• The pia matter extends upto the tip of the spinal

cord where it becomes filum terminale which

anchors the spinal cord to the sacrum

Subarachnoid space

• It is the space that lies between the arachnoid matter and pia matter

• It contains the CSF.

• This space communicates with the tissue spaces around the vessels in

the pia matter that accompany them as they penetrate into the

cord.These extensions of the subarachnoid space is termed as the

Virchow Robin Space.

• Its contents are CSF, nerve roots, blood vessels that suply the spinal cord

Subdural space

• The arachnoid is in close contact with the dural

sheath & is separated from it by a thin film of serous

fluid.

• Accidental placement of a catheter during epidural

anaesthesia and subsequent injection of local

anesthetic results in patchy anesthesia which is often

unilateral and extensive

Epidural space

• It is a space in the spinal canal that is occupied by dura and its

contents

• It Extends from the foramen magnum to end by the fusion of

its lining membranes at the sacrococcygeal membrane.

• It contains fat, vessels , nerve and lymphatics.

• Cranial epidural space is entirely empty.

• The distance from the skin to the lumbar epidural space in the

midline is on average about 5 cm.

Cerebrospinal fluid (CSF)

• The CSF is the clear

watery fluid contained

within the cerebral

ventricles and the

subarachnoid space.

• The total volume of CSF is

about 100 to 160ml in

adult humans and it is

produced at a rate of 20

to 25ml/hr

• CSF is an ultra filtrate formed by active process

from the choroid plexus of the lateral ventricles

• The epidymal cells of pia covering the blood

vessels play the secretary role

• At 600ml of CSF is formed per day

• About 20-25 ml of CSF is present in the ventricles

• 90 ml of the CSF in reservoirs in the brain

• 25-30 ml of CSF occupy the sub arachnoid space

• It is produced at a rate of 0.4ml/min

• It is around 25ml/hr

• About 4/5th of the fluid is reabsorbed via the

arachnoid villi.

• The remaining 1/5th of the CSF is absorbed via similar

spinal arachnoid villi or escapes along the nerve

sheaths in to the lymphatics.

• The specific gravity of CSF is 1.003-1.009

• Its PH is 7.4 - 7.6

• Na - 140-150 meq/L

• Chloride - 120-130 meq/L

• Bicarbonate - 25-30 meq/L

• Proteins – 15-45 mg/dl

• Glucose – 50-80 mg/dl

Spinal cord

• The adult spinal cord measures approximately 41 to 48

cm in length.

• Weight of spinal cord is between 24 to 36 gm.

• It is about 1 cm in diameter with cervical and

lumbosacral expansion.

• The spinal cord extends caudally from the brain. Its upper end

is continuous with the brain (medulla oblongata).

• In the newborn the spinal cord terminates in the lower border of 3rd

lumber vertebrae.

• In the adult spinal cord terminates at the disc between 1st and 2nd

lumber vertebrae.

• The spinal cord consists of 31 pairs of spinal nerves

• After L1 the nerve roots course for some distance before exiting the

intervertebral formina forming cauda equina (horse tail)

Cauda equina syndrome

• It is a lower motor neuron lesion which occurs due to the damage to

cauda equina

• It is caused due to trauma, tumours and lesions, spinal stenosis and

inflammatory conditions

• Symptoms include weakness of the muscles of the lower

extremities, urinary retention, fecal incontinence, sexual dysfunction

• Treatment of cauda equina syndrome is surgical decompression

Structure of spinal cord

• Spinal cord presents an

anterior median fissure and a

shallow posterior median

sulcus from which a glial

posterior median septum

extends half-way into the

substance of the cord.

Contd….In transverse section, the cord comprises a central canal an H-shaped zone of

grey matter(nerve cells) and an outer zone of white matter(nerve fibers).

• The H shaped grey matter is termed as the transverse commisure. Each

limb consists of an short broad anterior column (anterior horn) containing

large motor cells and thin pointed posterior column (posterior horn)

capped by substantia gelatinosa

• the amount of white matter declines progressively from cervical down to

the lumbar region.

• Grey matter is greatly increased in both cervical and lumbar enlargements,

which correspond to the zones of origin of motor nerves to the upper and

lower limbs.

• The central canal continues downwards from the 4th

ventricle as a narrow tube lined with ciliated ependymal

cells and contains csf

• It transverses the whole length of the cord, dilates

somewhat within the connus medularis and continues for a

short distance within the filum terminale

`

• The tracts that originate from the white matter of the spinal cord can be classified as Descending

tracts

Ascending tracts

• Descending tracts are

1. Lateral cerebrospinal or pyramidal tract

2. Anterior cerebrospinal or uncrossed motor tract

• Ascending tracts are

1. Posterior column

2. Spinothalamic tracts

3. Anterior and posterior spinocerebellar tracts

Blood supply of spinal cord

• The spinal cord is supplied by the anterior and posterior spinal arteries

which both descend down from the level of the foramen magnum

• The anterior spinal artery is formed at the level of the foramen magnum

by the union of the branch from each vertebral artery.

• It is the largest of the two arteries and it supplies the upper two third of

the spinal cord

• The posterior spinal arteries are paired arteries and they arise from the

posterior inferior cerebellar arteries

• They supply the posterior one third of the cord

• The anterior and posterior spinal arteries receive additional blood

supply from the intercoastal arteries in the thorax and lumbar

arteries in the abdomen

• One of these arteries is typically large which is the artery of

Adamakiewicz or arteria radicularis magna arising from the aorta

• It is typically unilateral and always arises on the left side providing

major blood supply to anterior and lower two third of the spinal

cord

Anterior Spinal artery syndrome

• Ischemia or infarction occurs in the spinal cord in the distribution of

the anterior spinal artery which supplies the anterior two third of

the spinal cord

• It s usually associated with atherosclerosis of the aorta

• It causes quadriparesis and impaired pain and temperature

sensation

• Complete motor paralysis below the level of lesion due to the

interruption of the corticospinal tract and loss of pain and

temperature below the level of the lesion

• The venous drianage comprises a plexus of

anterior and posterior spinal veins that drain

along the nerve roots through the intervertebral

foramina into the segmental veins azygos veins in

the thorax and lumbar veins in the abdomen and

lateral sacral veins in the pelvis

Spinal nerves

• There are 8 cervical nerves(C), 12 thoracic(T), 5 lumbar (L), 5

sacral (S), and 1 coccygeal .

• Each is formed by the fusion of an anterior & posterior

spinal root.

• Each pair of spinal nerves passes through a pair of

intervertebral foramina.

Layers of spinal nerve

• A series of connective tissue layer surrounds each

spinal nerve.

• Epineurium-outermost layer, consists of a dense

network of collagen fibers.

• Perineurium-extend inward from the epineurium,

dividing the nerve into a series of compartments.

• Endoneurium-delicate connective tissue fibers.

• The 31 pairs of spinal nerves each of them are composed

of anterior motor root and a posterior sensory root

• These nerve roots are compose of multiple rootlets

• The portion of the spinal cord that give rise to all of the

rootlets of a single spinal nerve is called as cord segment

• The skin area innervated by the given spinal nerve and its

corresponding cord segment is called a dermatome

SPINAL ANAESTHESIA

• Spinal anaesthesia is the regional anaesthesia obtained

by blocking the nerve roots in the subarachnoid space

• The spinal subarachnoid space extends from foramen

magnum to s2 in adults and s3 in children

HISTORY

• Corning accidentally administered cocaine intrathecally in order to

insert a catheter into the urethra in 1885

• The first spinal anaesthesia in humans was given by Beir from

Germany in 1898 using 0.5% cocaine.

• In 1908 Einhorm discovered procaine and synthetised the agent

• In 1905 Pitkin popularized the method of introducing the agents

intrathecally

STRUCTURES PIERCED

• The spinal needle is passed through the following structure…

1. Skin

2. Subcutaneous tissue

3. Supraspinous ligament

4. Interspinous ligament

5. Ligamentum flavum

6. duramater

Physiological responses on CVS

• Hypotension

• Symphathetic denervation

• Loss of vasomotor tone

• Arterial and venous dilation

• Decreased periperal vascular resistance and

peripheral pooling of blood

• Decreased venous return to heart and hence

hypotension

• Relaxation of the skeletal muscles of the leg

causes pooling of the blood and decreased

venous return to heart which results in

hypotension

• There occurs blockage of the cardio accelerator

fibres located in T1 to T4 and hence it causes

bradycardia and hypotension

Respiratory system

• There is a little effect on pulmonary function in patient

without pre-existing lung disease.

• Patient with severe chronic lung disease mainly rely upon

intercostals and abdominal muscles for respiration

• This causes relaxation of these muscles and thus causes

decrease in expiration and also associate with decreased

clearance of the tracheo bronchial secretions

AFFECTIVE DYSPNEA

• With the blockade of the sensory input patient may

complain of difficulty in breathing

• The mechanism is described as an inappropriate response

to the given muscular effort

• The patient believes that he/she is not exerting efforts

suficient to maintain breathing

• It is managed by asking the patient to take deep breaths,

providing supplementary oxygen

GASTRO INTESTINAL SYSTEM

• The gastrointestinal effect due to sympathetic blockade.

• The abdominal organ derive there sympathetic innervation from T6-L2.

• Blockade of these fibers result in unopposed parasympathetic activity by

vagus nerve.

• It increases the contractility of the gut with normal peristalsis and relaxed

sphincters

• Nausea is common complication of spinal and epidural.

• Shivering is commonly observed during spinal anaesthesia due to

decrease in core temperature which is the main cause of hypothermia

during spinal