Spinal anesthesia

Rahmeh Alsukkar

Anatomy

The vertebral column consists of 33 vertebrae: 7 cervical,

12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal

segments. The vertebral column usually contains three

curves. The cervical and lumbar curves are convex

anteriorly, and the thoracic curve is convex posteriorly

Five ligaments hold the spinal column together. The supraspinous

ligaments connect the apices of the spinous processes from the

seventh cervical vertebra (C7) to the sacrum. The supraspinous

ligament is known as the ligamentum nuchae in the area

above C7. The interspinous ligaments

connect the spinous processes together.

The ligamentum flavum, or yellow ligament, connects the laminae

above and below together. Finally, the posterior and anterior longitudinal ligaments bind the

vertebral bodies together.

The three membranes that protect the spinal cord are the dura

mater, arachnoid mater, and pia mater.

The dura mater, or tough mother, is the outermost layer.

The dural sac extends to the second sacral vertebra (S2). The arachnoid mater is the

middle layer, and the subdural space lies between the dural

mater and arachnoid mater. The arachnoid mater, or cobweb

mother, also ends at S2, like the dural sac. The pia mater, or soft mother, clings to the surface of the spinal cord and ends in the filum terminale, which helps to

hold the spinal cord to the sacrum.

The space between the arachnoid and pia mater is known as the

subarachnoid space, and spinal nerves run in this space, as does

CSF

Spinal Cord Extends from foramen magnum to

/upper in 1L of border lower : dultA

border of L2

Infants/children : L3

It is about 45 cm long

Duramater, Subarachnoid space &

subdural space: S2 in adults( S3 in

children)

S. C gives 31 pairs of spinal nerve

FILUM the , piamater of extension An

attach and dura the penetrate TERMINALE

the terminal end of spinal cord [conus

medullaris]to the periosteum of the coccyx

When preparing for spinal anesthetic blockade, it is important to accurately identify

landmarks on the patient

Derma

tomal

Level

Surface Landmark

C8 Little finger

T1,T2 Inner aspect of the arm

T4 Nipple line, root of

scapula

T7 Inferior border of

scapula ,Tip of xiphoid

T10 Umbilicus

L2 to

L3

Anterior thigh

S1 Heel of foot

Dermatomes

SURFACE ANATOMY

Anatomic Landmarks to Identify Vertebral

Levels

Anatomic

Landmark

Features

C7 Vertebral prominence, the most

prominent process in the neck

T7 Inferior angle of the scapula

L4 Line connecting iliac crests

S2 Line connecting the posterior

superior iliac spines

Sacral

hiatus

Groove or depression just above

or between the gluteal clefts

above the coccyx

Positions

Lateral Decubitus Position

A commonly used position for placing a spinal anesthetic is the lateral decubitus position.

Ideal positioning consists of having the back of the patient parallel to the edge of the bed

closest to the anesthesiologist, with the patient’s knees flexed to the abdomen and

neck flexed It is beneficial to have an assistant to help

hold and encourage the patient to stay in this position.

Sitting Position

The sitting position is utilized for low lumbar or sacral anesthesia and in instances when the

patient is obese and there is difficulty in finding the midline in the lateral position.

When performing a saddle block, the patient should remain in the sitting position for at

least 5 min after a hyperbaric spinal anesthetic is placed to allow the spinal to

settle into that region.

Prone Position

The prone position is utilized for spinal anesthesia if the patient needs to be in this position for the surgery, such as for rectal,

perineal, or lumbar procedures.

When performing a spinal anesthetic, appropriate

monitors should be placed, and airway and

resuscitation equipment should be readily available.

All equipment for the spinal blockade should be ready

for use, and all necessary medications should be drawn

up prior to positioning the patient for spinal anesthesia.

Adequate preparation for the spinal reduces the

amount of time needed to perform the block and assists

with making the patient comfortable.

Proper positioning is the key to making the spinal

anesthetic quick and successful.

Technique of Lumbar Puncture

Once the patient is correctly positioned, the midline

should be palpated. The iliac crests are palpated, and a

line is drawn between them in order to find the body of L4

or the L4-5 interspace.

Other interspaces can be identified, depending on where

the needle is to be inserted.

The skin should be cleaned with sterile cleaning solution,

and the area should be draped in a sterile fashion.

A small wheal of local anesthetic is injected into the skin

at the site of insertion.

More local anesthetic is then administered along the

intended path of the spinal needle insertion to a depth of 1

to 2 in.

1. MIDLINE APPROACH

2. PARAMEDIAN APPROACH

Midline Approach Paramedian

approach

Skin Skin

Subcutaneous fat Subcutaneous fat

Supraspinous ligament

Interspinous ligament

Ligamentum flavum Ligmentum flavum

Dura mater Dura mater

Subdural space Subdural space

Arachnoid mater Arachnoid mater

Subarachnoid space Subarachnoid space

Spinal : approaches

Structure Pierced

Midline Approach

The back should be draped in a sterile fashion.

The .felt are “pops” Two needle of advancement With

the is second & flavum .L the of penetration is first

penetration of dura-arachnoid membrane.

The stylet is then removed, and CSF should appear

at the needle hub.

For spinal needles of small gauge (26-29 gauge), this

usually takes 5-10 sec

Paramedian Approach

•Calcified interspinous ligament or difficulty in flexing the

spine

•The needle should be inserted 1 cm lateral and 1 cm

inferior of the superior spinous process of desired level.

Angle should be 10-25 toward midline

•The ligamentum flavum is usually the first resistance

identified.

SPINAL NEEDLE

QUINCKE WHITACRE SPROTEE

two Spinal needles fall into

main categories:

: duracut the ) those that i(

Quincke- Babcock

needle, the traditional

disposable spinal needle

(iI) those with a conical

tip(Pencil tip) : Whitacre

and Sprotte needles

If a continuous spinal

technique is chosen, use of

a Tuohy or Hustead needle

can facilitate passage of the

catheter

Blunt tip (pencil-point)

needle decreased the

incidence of PDPH

Sprotte is a side-

injection needle with a

long opening.

It has the advantage of

more vigorous CSF flow

compared with similar

gauge needles.

epidural anesthesia

Anatomy

Epidural Space

The epidural space is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels. The space is located just outside the dural sac which surrounds the nerve roots and is

filled with cerebrospinal fluid. •

Patient Positioning There are three positions used for the

administration of epidural anesthesia: sitting , lateral decubitus , and prone.

Sitting Position

1. Easier to identify midline, particularly in obese and scoliotic patients 2. Practitioners more experienced in sitting position 3. Shorter procedure time 4. Shorter distance from skin to epidural space 5. Greater cephalad spread of hypobaric solution

Advantages of sitting position

Lateral Decubitus Position

1. Sedation can be used more liberally Reduced patient movement 2. Increased patient comfort 3. Improved patient cooperation 4. Improved patient satisfaction 5. Reduced catheter displacementDecreased incidence of epidural vein cannulation 6. Attenuation of vagal reflexes 7. Hemodynamic changes better tolerated Bedside assistance may not be 8. required Intentional unilateral block for surgical procedures feasible

Using local anaesthetic raise a subcutaneous wheal at the midpoint between two adjacent vertebrae.

Inflitrate deeper in the midline and paraspinously to anaesthetise the posterior structures.

Insert epidural needle to the skin at this point, and advance through the supraspinous ligament, with the needle pointing in a slightly cephalad direction. Then advance the needle into the interspinous ligament,

which is encountered at a depth of 2-3 cm.until distinct sensation of increased resistance is felt as the

needle passes .

Technique of Epidural Anaesthesia

* With 5-10ml of air in the syringe, attach it to the hub of the needle once it has entered the interspinous ligament. The plunger is gently

pressed, and if there is resistance ("bounce"), the needle is very carefully advanced, with the dorsum of both hands resting against

the back to provide stability. * After 2-3mm, the plunger is again gently pressed, and this

procedure is repeated as the needle is carefully advanced through the tissues.

* The distinctive decrease in resistance when the needle enters the ligamentum flavum is felt, and the process is continued in 2mm

increments. * There is usually a distinctive "click" when the needle enters the

epidural space, and provided great care is taken, and the needle only advanced in 2mm increments, the needle should stop before it

reaches the dura. * At this point air can be injected into the epidural space very easily.

The syringe is removed and the catheter threaded as below.

* Remove the syringe and thread the catheter gently via the needle into the epidural space.

* The catheter has markings showing the distance from its tip, and should be advanced to 15-18cm at the hub of the needle, to ensure that a sufficient length of catheter has

entered the epidural space. * Remove the needle carefully, ensuring that the catheter is

not drawn back with it. * The markings on the needle will show the depth of the

needle from the skin to the epidural space, and this distance will help determine the depth to which the

catheter should be inserted at the skin. * For example, if the needle entered the epidural space at a

depth of 5cm, the catheter should be withdrawn so that the 10cm mark is at the skin, thus leaving approximately

5cm of the catheter inside the epidural space, which is an appropriate length.

There are four common approaches to the epidural space: midline, paramedian, Taylor

(modified paramedian), and caudal

approaches

With the midline technique, a Tuohy needle is introduced, directed slightly cephalad, through the skin in the midline

between the two spinous processes at the level of the desired block. The needle passes through the supraspinous ligament, the interspinous ligament and the fused pair of ligamentum flavae before it enters the epidural space. A

sudden ‘give’ may be felt as the needle tip exits the ligamentum flavum and enters the epidural space

Lateral deviation or a “wobbly” needle indicates that the needle is not properly engaged in ligament, necessitating

withdrawal and re-direction toward midline.

Midline and paramedian approaches

If a paramedian approach is chosen, the Tuohy needle is inserted through the skin at a point about 1.5 cm

lateral to the mid point of the spinous process immediately below the level of the desired block. The needle is advanced perpendicular to the skin, through

the underlying fat and muscle, until it strikes the vertebral lamina. It is then withdrawn slightly,

redirected cephalad and medially, and walked off the lamina until it pierces the ligamentum flavum and

enters the epidural space. The dura mater is held against the posterior wall of the vertebral canal by the pressure of the CSF inside the dura. Regardless of approach, on cannulation of the

epidural space the dura mater is indented by the tip of the Tuohy needle.

Epidural needle engaged in midline ligament

Paramedian epidural technique

Caudal technique

For regional blockade of the caudal epidural space the patient is usually

positioned in a lateral or prone position. The caudal space is approached through the tough sacrococcygeal ligament that covers the sacral hiatus. It is identified as a midline indentation in the sacrum at a point forming the

apex of an equilateral triangle made with the posterior superior iliac spines. For the caudal epidural technique a 23 or 21 G needle is placed

over the sacrococcygeal membrane at an angle of about 60o to the coronal plane and perpendicular to the other planes, with the bevel facing anteriorly to allow it to pass along the anterior sacral wall without piercing

it. There is usually a loss of resistance as the membrane is pierced. The needle should then be lowered to an angle of about 20o and advanced a short distance. The dura is not approximated to the point of needle entry

into the epidural space (as it is at other spinal levels), but is always at least 34 mm away in adults. Therefore a needle up to 25 mm long can be used safely without risk of dural puncture. In children, the dural sac is closer

and the needle should be advanced only a short distance

Taylor Approach

The Taylor approach is a modified paramedian approach utilizing the large L5–S1 interspace. It is an excellent approach for hip surgery or for any lower

extremity surgery in trauma patients who cannot tolerate the sitting position.

This approach may provide the only available access to the epidural space patients with ossified ligaments.in

1. With the patient in the sitting or lateral position, a skin wheal is placed

1 cm medial and 1 cm caudad to the posterior superior iliac spine. 2. The epidural needle is inserted into this site in a medial and cephalad

direction at a 45° to 55° angle. 3. As in the classic paramedian approach, the first resistance felt before

entry to the epidural space is on entry into the ligamentum flavum. 4. If the needle contacts bone (usually the sacrum), the needle should be walked off the bone into the ligament and then into the epidural space in progressively more medial and cephalad directions.patients with ossified

ligaments.