Spinal Anesthesia

PRESENTER – DR. MOHTASIB MADAOO

Introduction

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. The anesthesia

provider places the needle below L2 in the adult patient to avoid

trauma to the spinal cord. Spinal anesthesia provides excellent

operating conditions for:

Hernia (Inguinal or epigastric).

Haemorrhoidectomy , fistula , fissure.

Nephrectomy and cystectomy in combination with GA.

Transurethral resection of the prostate and transurethral resection of the

bladder tumors.

Abdominal and vaginal hysterectomies

Laparoscopic assisted vaginal hysterectomies(LAVH) combined with GA.

Caesarean sections.

Corning in 1885 , accidently administered cocaine

intrathecally.

Quincke in 1891 , made use of spinal puncture in

diagnosis.

August bier of Germany in 1898 , introduced the

technique of spinal anesthesia.

Pitkin popularized the method of introducing

agent's intrathecally.

History

Anatomy

A vertebra is composed of two parts

The body or base anteriorly, which bears

weight

The arch, which surrounds the cord

laterally and posteriorly consisting of

lamina and pedicles.

In addition there are seven processes or

projections

1. Three muscular processes – two transvers

and one spinous

2. Four articular processes, two upper and

two lower.

Anatomy of ligaments

Supraspinous ligament

The supraspionous ligament is a strong, thick,

fibrous band connecting the apices of the spines

from the seventh cervical to the sacrum.

Interspinous ligament

The interspinous ligament is thin, fibrous structure

connecting adjacent spines. The fibers are almost

membranous and extend from the apex and upper

surface of a lower spine toward the root and inferior

surface of the lower vertebrae.

Ligamentum flavum

The ligamentum flavum consists of yellow elastic

tissue. The fibers are perpendicular in direction.

They extend between lamina from the anterior

inferior surface of the upper lamina downward to

the anterior superior surface of the lower lamina.

Position of the Spinal Cord according to Age At 3 months of fetal life the tip of the cord is located at 2nd

coccygeal vertebrae.

At 6 months of fetal life the conus is at the level of S1.

At birth the tip of the spinal cord lies at the level of the

lower border of the L3 vertebra and the Dural sac at the S3

vertebra.

At one year of age the conus medullaris is at the lower border

of the L2 vertebra and the dural sac ends at the S2 vertebra.

By 12 to 16 years of age the adult relations are attained and

the spinal cord is located at the lower border of L1.

The average length of the spinal cord in the adult males is 45cm

and, in females, it is 42cm. The average weight approx. 30gm.

The spinal cord becomes relatively free of its dura but is

surrounded by the arachnoid and is engulfed in the CSF in the

subdural space. It also causes the downwards fanning of the

spinal nerves so that they run in an increasingly downward

oblique direction to form, at the lowest levels, the cauda

equina.

Physiology of CSF Cerebrospinal fluid (CSF) is produced by

the choroid plexus in the lateral, third, and fourth ventricles and circulates through the subarachnoid space between the arachnoid mater and the pia mater. The choroid plexus consists of projections of vessels and pia mater that protrude into the ventricular cavities as frond-like villi containing capillaries in loose connective stroma. A specialized layer of ependymal cells called the choroidal epithelium overlies these villi.

CSF is formed in the choroid plexus by both filtration and active transport. In normal adults, the CSF volume is 125 to 150 mL; approximately 25 to 30 ml occupy the spinal subarachnoid space. The normal rate of CSF production is approximately 25 mL per hour.

Dermatomes

A dermatome is an area of skin innervated by sensory fibers from a

single spinal nerve. To achieve surgical anesthesia for a given

procedure, the extent of spinal anesthesia must reach a certain

dermatomal level.

Dermatomal Levels of Spinal Anesthesia for Common Surgical

Procedures

Procedure Dermatomal Level

Upper abdominal surgery T4

Intestinal, gynecologic, and urologic surgery T6

Transurethral resection of the prostate T6

Vaginal delivery of a fetus, and hip surgery T10

Thigh surgery and lower leg amputations L1

Foot and ankle surgery L2

Perineal and anal surgery S2 to S5 (saddle block)

Positions for Spinal Tap Procedures

Approaches for Spinal Anesthesia Midline Approach. The most common approach, the needle

or introducer is placed midline, perpendicular to spinous

processes, aiming slightly cephalad.

Paramedian Approach. Indicated in patients who cannot

adequately flex because of pain or whose ligaments are

ossified, the spinal needle is placed 1.5 cm laterally and

slightly caudad to the center of the selected interspace. The

needle is aimed medially and slightly cephalad and passed

lateral to the supraspinous ligament. If the lamina is

contacted, the needle is redirected and "walked off" in a

medial and cephalad direction.

Taylor or Lumbosacral Approach. This approach is useful in

patients with calcified or fusion of higher intervertebral

spaces. The injection site is 1cm medial and 1cm caudad of

the posterior iliac spine. The needle is directed 45 degrees

medial and 45 degrees caudad, after contacting the lamina

the needle is walked upward and medially to enter the L5-S1

interspace

Technique

Midline Approach

The midline approach affords the practitioner two

advantages. Anatomic projection is only in 2 planes,

making visualization of the intended trajectory and

anatomical structures more apparent. The midline

provides a relatively avascular plane. It is important to

have the patient sitting up straight, not slumping to the

side, to minimize lumbar lordosis, and maximize the

space between the spinous processes. By proper

positioning you should have access to L2-L3, L3-L4, L4-L5,

and L5-S1. Identify the top of the iliac crest. Tuffier’s line

generally corresponds with the 4th lumbar vertebrae.

“Tuffier’s” line is a line drawn across the iliac crest

that crosses the body of L4 or L4-L5 interspace. This is

a helpful landmark for the placement of spinal or

epidural anesthetics.

Technique

Palpation in the midline should help to identify the interspinous

ligament. The extent of the space is noted by palpating the cephalad

and caudad spine. The midline is noted by moving your fingers from

medial to lateral.

Wash hands, put on sterile gloves, use sterile technique.

Prepare the tray in a sterile fashion. An assistant may help with

opening, in sterile fashion, specific items. Prepare the back with an

antiseptic. Start at the area of intended injection and move out. This

is done three times.

Place a skin wheal of local anesthetic at the intended spinous

interspace. Smaller gauge needles will require an introducer to

stabilize the needle. Place the introducer firmly into the interspinous

ligament.

Anatomical structures that will be transversed include skin,

subcutaneous fat, supraspinous ligament, interspinous ligament,

ligamentum flavum, epidural space, and dura.

Technique Hold the spinal needle like a dart/pencil. Cutting needles should be inserted

with the bevel parallel to the longitudinal fibers of the dura. This helps

reduce cutting fibers and enhances tactile sensation as anatomical structures

are crossed.

As the ligamentum flavum and dura are transversed, a change in resistance is

noted. Some will describe this as a “pop”; however, it may be a decrease in

pressure or a loss of resistance.

Once in the subarachnoid space, remove the stylet and CSF should appear. If

CSF does not appear, rotate the needle 90 degrees until it appears. If no CSF

appears then the stylet should be replaced. With smaller gauged needles it

may take 20-30 seconds for CSF to appear. Assess the needle position. Is it at

an appropriate depth? Is it midline or is its trajectory off the midline? Being

off the midline is one of the most common reasons that CSF does not come

back. If off the midline, remove the needle and start over.

If blood returns from the needle, wait to see if it clears. If it does not clear,

reassess needle position. If the needle is midline, not lateral, it may be in an

epidural vein. Advance the needle slightly further to transverse the dura. If

the needle is not midline, remove it and start over.

If bone is encountered, reassess the patient’s position and ensure the needle is midline. If bone is contacted early, the needle may be contacting the spinous process. Move the needle slightly caudad. If bone is contacted late, the needle may be contacting the lamina of the vertebrae. Move the needle slightly cephalad. Moving down an interspace may increase the chance of success since the intervertebral spaces will be larger.

After unsuccessful attempts, consider converting to a general anesthetic. The more attempts, the more trauma, increasing the risk of a spinal/epidural hematoma.

Once CSF returns, steady the needle with the dorsum of the non dominant hand against the patients back. Attach the syringe with the intended spinal anesthetic. Gently aspirate some CSF into the syringe. If a hyperbaric technique is being used, a “swirling” in the solution will be noted due to the dextrose content. Aspiration with an isobaric technique will yield additional CSF fluid into the syringe. The cerebral spinal fluid should be clear. If blood is returned with aspiration, replace the styletand start over.

Inject the local anesthetic at a rate of 0.2 ml per second. After injection aspirate 0.2 ml of CSF to confirm that the needle remains in the subarachnoid space. If the patient complains of pain during injection, stop immediately. Redirect the needle away from the side of pain and into the midline.

Place the patient in the appropriate position for the procedure and baricity of the spinal anesthetic solution.

TechniqueParamedian Approach

The advantage of the paramedian approach is a larger target. By placing the

needle laterally, the anatomical limitation of the spinous process is avoided. The

most common error when attempting this technique is being too far from the

midline, which makes encountering the vertebral lamina more likely.

Palpate the vertebral process and identify the caudad tip. Move 1 cm down

and 1 cm laterally.

Prepare the back with an antiseptic solution. Place a skin wheal of local

anesthetic at the identified area of needle insertion. A longer needle is often

required to infiltrate the tissue.

Insert the spinal needle 10-15 degrees off the sagittal plane. At this point the

most common error is inserting the needle too far cephalad, which results in

encountering the lamina of the vertebral body. If bone is contacted, redirect

the needle a little further caudad.

It may be possible to feel the characteristic change in resistance or loss of

resistance. With a lateral approach the needle is inserted further than with

the midline approach.

Once CSF is obtained, continue in the same manner as the midline approach.

Taylor’s Technique

This is a very useful method in cases of spine fusion, arthritic spine, skin

infection in the lumbar region, or in other conditions in which the usual

approach is difficult or impossible.

Largest interspace L5-S1.

A skin wheal is made 1cm medially and 1cm below the lowest prominence of

the posterior-superior spine. A 12-cm , needle is directed upward , medially

and forward at an angle of about 50degree , approximating forward at an

angle that the dorsal aspect of the sacrum makes with the skin. The needle

then is advanced so that it’s point enters the lumbosacral space between the

sacrum and the last lumbar vertebra. As the space is entered , there usually

an immediate flow of CSF , although gentle aspiration may be necessary.

PRINCIPLES IN ADMINISTRATING ANAESTHETIC

SOLUTIONS

Main aim of anaesthetists is to secure anaesthesia of

Sufficient duration

Sufficient Height

STOUT’S PRINCIPLES FOR SPREAD OF SOLUTIONS

Height of anaesthesia is

Directly proportional to concentration of the drug

Inversely proportional to rapidity of fixation

Directly to speed of injection

Directly proportional to the volume of fluid.

Inversely proportional to spinal fluid pressure.

Directly proportional to specific gravity for hyper baric solution.

With isobaric or hypobaric solutions, extent depends on position of patient.

FACTORS POSTULATED TO BE RELATED TO

SPINAL ANAESTHETIC BLOCK HEIGHT

PATIENT CHARACTERISTICS

Age, Height, Weight, Intra abdominal pressure, position, anatomic

configuration of spinal column.

TECHNIQUE OF INJECTION

Site of injection, direction of injection, rate of injection.

CHARACTERISTICS OF SPINAL FLUID

Volume, Pressure, density.

CHARACTERISTICS OF ANAESTHETIC SOLUTIONS

Density, Amount, Concentration, temperature, volume.

PATIENT FACTORSAGE

Spinal space become smaller with age - distribution greater.

OBESITY

Increase intra-abdominal pressure

increase pressure in epidural space.

Decrease subarachnoid space

PREGNANCY

Increase intra-abdominal pressure

Increase volume of epidural venous plexus - Small subarachnoid spaces.

INTRAABDOMINAL PRESSURE

Changes resulting from direct pressure of increased intra-abdominal pressure on epidural and subarachnoid spaces.

Collateral flow through epidural venous plexus expand- SA space small

SPINAL CURVATURE

Abnormal curvature have an effect on technical aspects

Changes the contour of Subarachnioid space

RATE OF INJECTION

Slow injections - low levels

Rapid injections - high level

DENSITY / SPECIFIC GRAVITY AND BARICITY

Density of any solution is the weight in grams of 1 ml of the solution at a

standard temperature. Density varies inversely with temperature.

Specific gravity is the density of a solutions compared in a ratio with the

density of water.

Baricity is a ratio comparing the density of one solution to another.

Density of normal human. CSF at 370C is 1.0001 to 1.0005

Specific gravity of spinal fluid 1.003 to 1.008

ISOBARIC SOLUTIONS

Densities between 0.9998 and 1.0008

Solutions are mixed with physiological saline

Solutions with out added glucose

Bupivacaine, ropivacaine, levobupivacaine

Spread not influenced by position

HYPOBARIC SOLUTIONS

Baricity less than 0.9998 at 370C

Prepared by diluting with distilled water

HYPERBARIC SOLUTIONS

Solutions at 37degree Celsius with baricity greater than 1.0008

Made by addition of 5-9.5% dextrose

They show bimodal spread – gravitate from the site of injection to two

different directions i.e., to the point below L3 into the lumbosacral concavity

or above L3 into the thoracic concavity to the T5 level.

Travel to the most dependent part of the subarachnoid space when there is

deviation of the patients position from the horizontal.

Barbotage

This is the technique of stirring up to increase turbulence , mixing of injected

solutions and increasing the distribution in the subarachnoid space.

The technique first was described by Bier and consists of the injection of the

anesthetic solution into the subarachnoid space, immediate withdrawal of a

portion of the solution and reinjection. This may be repeated. The to-and-fro

movement agitates the injectate in the spinal fluid, and the currents mix the

agent more completely and carry the agent more extensively and to higher

levels.

Caution must be observed and each operator must learn the results of his

barbotage

Types of Spinal Needles

Whitacre Pencil Point Spinal Needles

Help Reduce Post-Procedure Headaches

Designed to spread the dural fibers and help reduce the occurrence of post

dural puncture headache

Distinct "pop" as the pencil point penetrates the dura

Precision-formed side hole helps directional flow of anesthetic agents and

helps reduce the possibility of straddling the dura

Designed to track straight when advancing through ligaments toward the dura

Translucent window hub features contact clarity that helps allow visualization

of CSF

Needle gauges 22 to 27 G.

Needle lengths 3½ in. to 5 in.

Quincke Needles

Key/Slot arrangement of stylet and cannula hubs facilitates proper needle

bevel orientation

Translucent window hub features contact clarity that helps allow visualization

of CSF

Fitted stylet reduces tissue coring

Needle gauges 18 to 27 G.

Needle lengths 1 in. to 7 in.

Spinal Anesthesia – Physiologic

Effects

Somatic Blockade

Neuraxial anesthesia effectively stops the transmission of painful sensation

and abolishes the tone of skeletal muscle, enhancing operating conditions for

the surgeon.

Sensory blockade involves somatic and visceral painful stimulation. Motor

blockade involves skeletal muscles. Neuraxial anesthesia results in a

phenomenon known as differential blockade. This effect is due to the activity

of local anesthetics and anatomical factors.

Local anesthetic factors include the concentration and duration of contact

with the spinal nerve root. As the local anesthetic spreads out from the site of

injection the concentration becomes less, which may in turn effect which

nerve fibers are susceptible to blockade. Anatomical factors are related to

various fiber types found within each nerve root. Small myelinated fibers are

easier to block than large unmyelinated fibers.

In general, the differential blockade found after neuraxial blockade is as

follows: sympathetic blockade is 2-6 dermatome segments higher than

sensory and sensory blockade is generally 2 dermatome levels higher than

motor.

Sequence of Nerve Modality Block

1. Vasomotor Block – dilatation of skin vessels and increased cutaneous blood

flow

2. Block of cold temperature fibers

3. Sensation of warmth by patient – the “hot foot” phenomenon

4. Temperature discrimination is next lost

5. Block of somatic sensory fibers occurs next with slow and fast pain loss

6. Tactile sense is lost

7. Somatic motor fibers are then blocked along with pressure and

proprioception.

Bromage Scale – Intensity of Motor Block

Autonomic Blockade

Neuraxial blockade effectively blocks efferent autonomic transmission of the

spinal nerve roots, producing a sympathetic block and a partial

parasympathetic block.

Sympathetic fibers are small, myelinated, and easily blocked. During

neuraxial blockade, the anesthesia provider will observe a sympathetic block

prior to sensory, followed by motor.

The sympathetic nervous system (SNS) is described as thoracolumbar since

sympathetic fibers exit the spinal cord from T1 to L2.

The parasympathetic nervous system (PNS) has been described as craniosacral

since parasympathetic fibers exit in the cranial and sacral regions of the CNS.

The end result of neuraxial blockade is a decreased sympathetic tone with an

unopposed parasympathetic tone. This imbalance will result in many of the

expected alterations of normal homeostasis noted with the administration of

spinal anesthesia.

Cardiovascular Effects

Neuraxial blockade can impact the cardiovascular system by causing the

following changes:

Decrease in blood pressure (33% incidence of hypotension in non-obstetric

populations)

Decrease in heart rate (13% incidence of bradycardia in non-obstetric

populations)

Decrease in cardiac contractility

Respiratory Effects Neuraxial blockade plays a very minor role in altering pulmonary function.

Even with high thoracic levels of blockade, tidal volume is unchanged. There is a slight decrease in vital capacity. This is the result of relaxation of the abdominal muscles during exhalation.

The phrenic nerve is innervated by C3-C5 and is responsible for the diaphragm. The phrenic nerve is extremely hard to block, even with a high spinal. In fact, apnea associated with a high spinal is thought to be related to brainstem hypoperfusion and not blockade of the phrenic nerve. This is based on the fact that spontaneous respiration resumes after hemodynamic resuscitation has occurred.

The risk and benefits of neuraxial anesthesia should be carefully weighed for the patient with severe lung disease. Patients with chronic lung disease depend on intercostal and abdominal muscles to aid their inspiration and exhalation. Neuraxial blockade may reduce the function of these muscles, having a detrimental impact on the patient’s ability to breathe, as well as affect the ability to clear secretions and cough. For procedures above the umbilicus, a pure regional anesthetic may not be beneficial for the patient with chronic lung disease.

Thoracic and abdominal surgical procedures are associated with decreased phrenic nerve activity resulting in decreased diaphragmatic function and FRC (functional reserve capacity). This can lead to atelectasis and hypoxia due to ventilation/perfusion mismatching

Gastrointestinal Effects Since sympathetic outflow originates at T5-L1, neuraxial blockade results in a

sympathectomy with a predomination of parasympathetic nervous system

effects. The end result is a small, contracted gut with peristalsis.

Hepatic blood flow decreases in relation to decreases in mean arterial

pressure but does not differ significantly from other anesthetic techniques.

Renal Effects

Neuraxial blockade has little effect on the blood flow to the renal system.

Autoregulation maintains adequate blood flow to the kidneys as long as

perfusion pressure is maintained.

Neuraxial blockade effectively blocks sympathetic and parasympathetic

control of the bladder at the lumbar and sacral levels. Urinary retention can

occur due to the loss of autonomic bladder control. Detrusor function of the

bladder is blocked by local anesthetics. Normal function does not return until

sensory function returns to S3.

Complications IntraOP

and PostOP

Complications IntraOP and PostOP

IntraOP

1. Hypotension

2. Respiratory impairment

3. Nausea and Vomiting

4. Total Spinal

PostOP

1. Post Dural Puncture Headache

2. Infections

Treatment of Hypotension

Hypotension is due to vasodilation and a functional decrease in the effective

circulating volume.

1.Vasopressors

2.All hypotensive patients should be given OXYGEN by mask until the blood

pressure is restored.

Ephedrine 2.5-6mg titrated against the blood pressure. Its effect generally

lasts about 10 minutes and it may need repeating.

It can also be given intramuscularly but its onset time is delayed although its

duration is prolonged..

Phenylephrine.

Noradrenaline.

Adrenaline/Epinephrine.

Increase the rate of the intravenous infusion to maximum until the blood

pressure is restored to acceptable levels.

Complications

Respiratory impairment

Related to high spinal levels with ascending blockade of the thoracic and the

cervical segments(intercostal and phrenic nerves). A progressive ascending

paralysis of the intercostal muscles and diaphragm ensues. This leads to

respiratory insufficiency and apnea.

Treatment of Total Spinal.:

1. Hypotension - Remember that nausea may be the first sign of hypotension. Give

vasopressors.

2. Bradycardia – Administer atropine

3. Increasing anxiety - reassure.

4. Numbness or weakness of the arms and hands, indicating that the block has

reached the cervico-thoracic junction.

5. Difficulty breathing - as the intercostal nerves are blocked the patient may state

that they can't take deep breaths. As the phrenic nerves (C 3,4,5) which supply the

diaphragm are blocked, the patient will initially be unable to talk louder than a

whisper and will then stop breathing.

6. Loss of consciousness.

Ask for help - several pairs of hands may be useful!

Intubate and ventilate the patient with 100% oxygen.

Once the airway has been controlled and the circulation restored, consider

sedating the patient with a benzodiazepine.

Nausea and Vomiting

Often due to sudden change in position. Nausea and Vomiting accompany

hypotension and are related to the hypoxia., excessive rise in Blood pressure

following administration of a vasopressor is also prone to produce nausea.

ComplicationsHeadache (PDPH): .

A characteristic headache may occur following spinal anaesthesia. It begins

within 24-72 hours and may last a week or more.

It is postural, being made worse by standing or even raising the head and

relieved by lying down.

It is often occipital and may be associated with a stiff neck. Nausea,

vomiting, dizziness and photophobia frequently accompany it.

It is more common in the young, in females and especially in obstetric

patients.

It is thought to be caused by the continuing loss of CSF through the hole made

in the dura by the spinal needle. This results in traction on the meninges and

pain.

The incidence of headache is related directly to the size of the needle used. A

16 gauge needle will cause headache in about 75% of patients, a 20 gauge

needle in about 15% and a 25 gauge needle in 1-3%.

As the fibres of the dura run parallel to the long axis of the spine, if the bevel

of the needle is parallel to them, it will part rather than cut them and

therefore, leave a smaller hole.

It is widely considered that pencil-point needles (Whitacre or Sprotte) make a smaller hole in the

dura and are associated with a lower incidence of headache (1%) than conventional cutting-edged

needles (Quincke)

Treatment of PDPH

Positive reassurance of recovery

Confinement to bed. Head down position may be necessary.

Hydration therapy – Oral as well as Intravenous.

Analgesics and Antiemetics – Paracetamol, Aspirin, Codeine, Ondasentron.

Abdominal binders – Raises pressure in peridural venous plexus and thereby

increasing CSF pressure.

Oxygen inhalations.

Caffeine containing drinks such as tea, coffee are often helpful.

Prolonged or severe headaches may be treated with epidural blood patch

performed by aseptically injecting 15-20ml of the patient's own blood into the

epidural space. This then clots and seals the hole and prevents further

leakage of CSF.

Sources

Principles of Anesthesiology: General and Regional Anesthesia - Vincent J.

Collins

Morgan and Mikhail's Clinical Anesthesiology

NYSORA

IJA

BJA

Oxford Journal of Anaesthesia

http://www.pitt.edu/

Thanks for Your

Attention.