SPINAL AND SPINAL AND EPIDURAL EPIDURAL

ANESTHESIAANESTHESIA

DEPARTMENT OF ANESTHESIA

OSPITAL NG MAYNILA MEDICAL CENTER

GOOD GOOD MORNING!!MORNING!!

!!

EPIDURAL AND SPINAL EPIDURAL AND SPINAL ANESTHESIAANESTHESIA

• No absolute indications

• Clinical situations, patient physiology, surgical procedure: makes central neuraxial block the technique of choice

EPIDURAL AND SPINAL EPIDURAL AND SPINAL ANESTHESIAANESTHESIA

• Blunt the “stress response” to surgery – decrease intraoperative blood loss – lower the incidence of postoperative

thromboembolic events – decrease morbidity and mortality in

high-risk surgical patients

• extend analgesia into the postoperative period (provide better analgesia than can be achieved with parenteral opioids)

• provide analgesia to non-surgical patients

ANATOMYANATOMY

VERTEBRAEVERTEBRAE

The spine consists of 33 vertebrae

• 7 cervical • 12 thoracic• 5 lumbar • 5 fused sacral • 4 fused coccygeal

• Cervical (except C1), thoracic, and lumbar vertebrae: body anteriorly, two pedicles that project posteriorly from the body, and two laminae that connect the pedicles ----form the vertebral canal, which contains the spinal cord, spinal nerves, and epidural space

• Lamina: give rise to the transverse processes (laterally); spinous process (posteriorly) --- sites for muscle and ligament attachments

• Pedicles: contain a superior and inferior vertebral notch through which the spinal nerves exit the vertebral canal

5 sacral vertebrae fused to form the wedge-shaped sacrum (connects the spine with the iliac wings of the pelvis)

• 5th sacral vertebra (not fused posteriorly) give rise to a variably shaped opening ---- sacral hiatus opening into the sacral canal (caudal termination of the epidural space)

Sacral cornu• bony prominences on either side of the hiatus• aid in identification of sacral hiatus

Coccyx• fused 4 rudimentary coccygeal vertebrae• a narrow triangular bone that abuts the sacral

hiatus

• Tip of the coccyx can often be palpated in the proximal gluteal cleft and by running one’s finger cephalad along its smooth surface, the sacral cornu can be identified at the 1st bony prominence encountered

C7 : 1st prominent spinous process encountered while running the hand down the back of the neck

T1 : most prominent spinous process

T12 : can be identified by palpating the 12th rib and tracing it back to its attachement to T12

Line drawn between the iliac crests: •body of L5 or the 4-5 interspace

LIGAMENTSLIGAMENTS

• Vertebral bodies are stabilized by 5 ligaments that increase in size between the cervical and lumbar vertebrae

EPIDURAL SPACEEPIDURAL SPACE• Space that lies between the spinal

meninges and the sides of the vertebral canal

• Boundaries:– Cranially: foramen magnum– Caudally: sacrococcygeal ligament covering

the sacral hiatus– Anteriorly: posterior longitudinal ligament– Laterally: vertebral pedicles– Posteriorly: ligamentum flavum and vertebral

lamina

• Not a closed space but communicates with the paravertebral space by way of the intervertebral foramina

• Shallowest anteriorly where the dura may in some places fuse with the posterior longitudinal ligament

• Deepest posteriorly

• Composed of a series of discontinuous compartments that become continuous when the potential space separating the compartments is opened up by injection of air or liquid

MENINGESMENINGES

• Spinal meninges consist of 3 protective membranes :– Dura mater– Arachnoid mater– Pia mater

Dura mater• Outermost and thickest meningeal

tissue• Begins at the foramen magnum; ends

at approx S2 where it fuses with the filum terminale

• Inner surface abuts the arachnoid mater

Arachnoid mater• Delicate, avascular membrane

composed of overlapping layers of flattened cells with connective tissue fibers running between the cellular layers

• Specialized connections (tight junctions and occluding junctions) account for the fact that it is the physiologic barrier for drugs moving between the epidural space and the spinal cord

• Subarachnoid space lies between the arachnoid mater and the pia mater and contains the CSF

• Spinal CSF is in continuity with the cranial CSF and provides an avenue for drugs in the spinal CSF to reach the brain

• Spinal nerve roots and rootlets run in the subarachnoid space

Pia mater• Adherent to the spinal cord and is

composed of a thin layer of connective tissue cells interspersed with collagen

• Extends to the tip of the spinal cord where it becomes the filum terminale, which anchors the spinal cord to the sacrum

• Gives rise to the dentate ligaments

TECHNIQUETECHNIQUE

NEEDLESNEEDLES

NEEDLESNEEDLESSpinal NeedlesWhitacre and Sprotte: • “pencil-point” tip• needle hole on the

side of the shaft

Greene and Quincke: beveled tips with cutting edges

Spinal Needles• * pencil-point needles

require more force to insert than the bevel-tip needles but provide better tactile “feel”; not deflected* Size: 22-29 gauge larger

gauge smaller diameter

Epidural Needles• Touhy: curved tip to

help control the direction that the catheter moves in the epidural space

• Hustead: less curved tip

• Crawford: straight; less suitable for catheter insertion

*sizes: 16-19 gauge

SEDATIONSEDATION• Light sedation before placement of block

– Successful spinal and epidural anesthesia requires patient participation to:•maintain good position•evaluate block height•indicate paresthesias if needle contacts

neural elements•properly evaluate an epidural test

• Once the block is placed and adequate block height assured, patient can be sedated as deemed appropriate

SPINAL ANESTHESIASPINAL ANESTHESIAPOSITIONPatient positioning is critical to

successful spinal puncture• lateral decubitus • sitting position • prone jackknife position

POSITIONLateral decubitus• patient lies with the operative side

down (hyperbaric LA) • or with operative side up (hypobaric

LA) ---most dense block occurs on the operative side

POSITION

– back at the edge of the table– patient’s shoulders and hips positioned

perpendicular to the bed– knees drawn to the chest; neck flexed;

patient instructed to curve the back outward

MIDLINE APPROACH• Skin overlying the desired interspace is

infiltrated with a small amount of LA (1-2 ml) to a depth of 1-2 inches to prevent pain when inserting the spinal needle

• Slight cephalad angulation (10-15 degrees)

MIDLINE APPROACHNeedle is then advanced • subcutaneous tissue • supraspinous ligament • interspinous ligament• ligamentum flavum• epidural space • dura mater• arachnoid mater

MIDLINE APPROACH

MIDLINE APPROACHPenetration of the dura mater produces a

subtle “pop”– detection of dural penetration

• prevent inserting the needle all the way through the subarachnoid space and contacting the vertebral body;

– insert spinal needle quickly without having to stop every few mm and remove the stylet to look for CSF at the needle

MIDLINE APPROACHOnce the needle tip is believed to be in the

subarachnoid space, stylet is removed to see if CSF appears at the needle hub– Small diameter needles (26-29 gauge)

requires 5-10 sec or >/= 1 minute

• Failure to obtain CSF suggests that the needle orifice is not in the subarachnoid space and must be reinserted

MIDLINE APPROACHOnce the needle is correctly inserted into

the subarachnoid space, it is fixed in position and the syringe containing LA is attached

CSF is gently aspirated to confirm that the needle tip remained in the subarachnoid space and LA slowly injected (</=0.5 ml/s-1)

MIDLINE APPROACHAfter completing the injection, a small

volume of CSF is again aspirated to confirm that the needle tip remained in the subarachnoid space while the LA was deposited

This CSF is then reinjected and the needle, syringe, and any introducer removed together as a unit

MIDLINE APPROACHstrict attention to patient’s hemodynamic

status with BP and/or HR supportedblock height should also be assessed early

– pin prick – temperature sensation

–Table may be tilted as appropriate to influence further spread of local anesthetics

PARAMEDIAN APPROACH• useful in situations where the patient’s

anatomy does not favor the midline approach – inability to flex the spine– heavily calcified interspinous ligaments

• Patient in any position; best approach for the patient in the prone jackknife position

PARAMEDIAN APPROACH• Identify the spinous process forming

the lower border of the desired interspace

• Needle inserted – ~1 cm lateral – directed toward middle of the interspace

~45 degrees cephalad – medial angulation (~15 degrees) to

compensate for the lateral insertion point

PARAMEDIAN APPROACH

•Needle inserted ~1 cm lateral, directed toward middle of the interspace ~45 degrees cephalad with just enough medial angulation (~15 degrees) to compensate for the lateral insertion point

PARAMEDIAN APPROACH1st significant resistance encountered:

ligamentum flavumAlternative method:

– insert needle perpendicular to the skin in all planes until the lamina is contacted; needle is then walked off the superior edge of the lamina and into the subarachnoid space

**Lamina provides a valuable landmark that facilitates correct needle placement

EPIDURAL ANESTHESIAEPIDURAL ANESTHESIA• May be performed at

any intervertebral space

• LA skin wheal is raised to the point of needle insertion

• Pierce the skin with a >/=18 G hypodermic needle

• Epidural needle inserted through the subcutaneous tissue and into the interspinous ligament “gritty feel”

• Needle is advanced slowly until an increase in resistance is felt : ligamentum flavum

Techniques to identify epidural space:– Loss of resistance

technique (fluid/air)• Glass syringe: 2-3 ml

saline + 0.1-0.3 ml air bubble

– Hanging drop technique

After entering the epidural space, stop advancing the needle– heightens the risk of meningeal puncture

“wet tap”

• LA test dose should be administered to help rule out undectected subarachoid or IV needle placement

• After a negative test dose, desired volume should be administered in small increments

EPIDURAL TEST DOSE– To identify epidural needles or catheters

that have entered an epidural vein or the subarachnoid space

– Failure to perform: IV injection or total spinal block

– 3 ml of LA + 1:200,000 epinephrine• IV: epinephrine

– HR increases 20-40 sec after– BP increase of >/=20 mmHg

• Subarachnoid: motor block ---LA

PHYSIOLOGYPHYSIOLOGY

• Spinal anesthesia interrupts sensory, motor, and sympathetic nervous system

• Classic concept:– Conduction blockade through small diameter

unmyelinated (sympathetic) fibers before interrupting conduction via large myelinated (sensory & motor) fibers

• Block of afferent impulses from the surgical site leads to absence of adrenocortical response to pain

Cardiovascular system• Vasodilatation of resistance and capacitance

vessels occurs: hypovolaemia, tachycardia, drop in blood pressure – exacerbated by blockade of the

sympathetic nerve supply to the adrenal glands, preventing the release of catecholamines.

• Bradycardia: If blockade is as high as T2, sympathetic supply to the heart (T2-T5)

• overall result: inadequate perfusion of vital organsmeasures: restore blood pressure and cardiac output (fluid administration, vasoconstrictors)

• Sympathetic outflow extends from T1 - L2 (blockade of nerve roots below this level, knee surgery, is less likely to cause significant sympathetic blockade, compared with procedures requiring blockade above the umbilicus)

Respiratory system• usually unaffected unless blockade is high

enough to affect intercostal muscle nerve supply (thoracic nerve roots) leading to reliance on diaphragmatic breathing alone

• distress to the patient, as they may feel unable to breathe adequately

• decreased ability to cough and expel secretions

• if patients cannot breathe, ventilate (face mask and bag

Gastrointestinal system• Blockade of sympathetic outflow (T5-L1),

leads to predominance of parasympathetic (vagus and sacral parasympathetic outflow)– leading to active peristalsis and relaxed

sphincters, and a small, contracted gut, which enhances surgical access

– Splenic enlargement (2-3 fold) occurs

• If above T5, inhibits sympathetic innervation to the GIT, resulting in unopposed parasympathetic nervous system activity– Contracted intestines and relaxed sphincter; if not

on NPO, tendency to develop vomiting

Genitourinary tract• urinary retention is a common problem • severe drop in blood pressure may affect

glomerular filtration in the kidney (if sympathetic blockade extends high enough to cause significant vasodilatation)

• ureters are contracted and ureterovesical orifice is relaxed

• Decreased bleeding may be a reflection of decreased BP

• Increased blood flow to lower extremities ---- decreased incidence of thromboembolism

• BLOCK HEIGHTSURGICAL

PROCEDURESUGGESTED

BLOCK HEIGHTTECHNIQUE

PerianalPerirectal

L1-2 Hyperbaric/sitting posHypobaric/jackknife pos

Lower extremity/ HipTURPVaginal/ cervical

T10 Isobaric

HerniorrhaphyPelvic proceduresAppendectomy

T6-8 Hyperbaric/ horizontal

AbdominalCesarean section

T4-6 Hyperbaric/ horizontal

FACTORS THAT AFFECT SPREAD OF LOCAL FACTORS THAT AFFECT SPREAD OF LOCAL ANESTHETIC SOLUTIONSANESTHETIC SOLUTIONS

Characteristics of the local anesthetic solution– Baricity: ratio of density (mass/vol) of LA div

density of CSF– Local anesthetic dose– Local anesthetic concentration– Volume injected

Patient characteristicsAge WeightHeightGenderPregnancyPatient position

FACTORS THAT AFFECT SPREAD OF LOCAL FACTORS THAT AFFECT SPREAD OF LOCAL ANESTHETIC SOLUTIONSANESTHETIC SOLUTIONS

Technique– Site of injection

Diffusion

Speed of injectionBarbotageDirection of needle bevelAddition of vasoconstrictors

LOCAL ANESTHETIC LOCAL ANESTHETIC SOLUTIONSOLUTION

• HYPERBARIC: solution more dense than CSF; >/=1.0015– Add glucose (5-8% dextrose) of increase the

density– LA solution settles to dependent region

• HYPOBARIC: solution less dense than CSF; <0.9990– Add sterile/distilled water; floats up to the nerves

innervating surgical site

• ISOBARIC: same density; 1.0000– Dilute with CSF or normosaline solution

COMPLICATIONSCOMPLICATIONS

• Hypotension• Postdural puncture headache• Hearing loss• Total spinal• Backache• nausea• Urinary retention• Systemic toxicity• Neurologic injury• Spinal hematoma

• Hypotension– Due to sympathetic nervous system

blockadea.Decreased venous return to heart,

decreased cardiac outputb.Decreased systemic vascular resistancec.Bradycardia due to blockade of

cardioaccelerator fibers (T1-3), decreased cardiac output

• HypotensionTreatment: restore venous return to incrase

cardiac output– Position head-down: autotransfusion– Hydration before spinal anesthesia– Sympathomimetics

• Postdural puncture headache– Frontal/occipital– Worsened by sitting, improved by supine position– Due to decreased CSF pressure and resulting

tension on meningeal vessels and nerves as a result of leakage of CSF through the dural hole

– Diplopia due to traction on abducens nerve– Treatment: bed rest, analgesics

• Hydration (>/= 3L/day) to increase CSF production• Epidural patch (10-20 ml) to seal dura• Caffeine-sodium benzoate (by vasoconstriction)

• Hearing loss

• High Spinal– Undesired excessive level of sensory and

motor anesthesia associated with difficulty of breathing or apnea --- arterial hypoxemia or hypercarbia

– Apnea reflects ischemic paralysis of medullary ventilatory centers due to profound hypotension and associated with decreased cerebral blood flow

• High Spinal– Treatment: support breathing and

circulationa. Positive pressure ventilation with face maskb. IVF and sympathomimeticsc. Head down to increase venous return(head up will jeopardize cerebral blood flow ---

medullary ischemiad. Intubation of trachea in those at risk for

aspiration

•Total spinal – rare complication– profound hypotension– apnea– unconsciousness– dilated pupils as a result of the action of

local anesthetic on the brainstem

• Management– Airway – secure, administer 100% oxygen – Breathing - ventilate by facemask, intubate – Circulation - treat with iv fluids and vasopressor – Continue to ventilate until the block wears off (2 -

4 hours) – As the block recedes the patient will begin

recovering consciousness followed by breathing and then movement of the arms and finally legs. Consider some sedation (diazepam 5 - 10mg i/v) when the patient begins to recover consciousness but is still intubated and requiring ventilation

• Backache– May be related to position required for

surgery– More likely due to ligamentous strain

when in an uncomfortable position

• Nausea– May be due to hypotension --- cerebral

ischemia; tx sympathomimetics– May be due to predominance of

parasympathetic nervous system activity; tx atropine 0.4 mg IV

• Urinary Retention– Because spinal anesthesia interferes with

innervation of the bladder– Administration of large amounts of fluid ---

bladder distention requiring catheter drainage

• Systemic toxicity

• Neurologic injury– Very rare due to small dose of LA

employed– In the absence of hematoma or abscess,

treatment is symptomatic

• Spinal hematoma– Rare; present with numbness or LE

weakness– Risk factor: coagulation defects

• Inadvertent high epidural block – due to an excessively large dose of local

anesthetic– hypotension, nausea, sensory loss or

paresthesia of high thoracic or even cervical nerve roots (arms), or difficulty breathing

– most severe cases may require induction of GA with securing of the airway, while treating hypotension

– If patient has a clear airway and is breathing adequately: reassurance and any hypotension immediately treated

– Difficulty in talking (small tidal volumes due to phrenic block) and drowsiness are signs that the block is becoming excessively high and should be managed as an emergency

• Local anesthetic toxicity – excessive dose of local anaesthetic– moderate dose of LA, injected directly into

a blood vessel– epidural catheter is inadvertently

advanced into one of the many epidural veins. It is therefore vital to aspirate from the epidural catheter prior to injecting local anaesthetic

– symptoms: light-headedness, tinnitus, circumoral tingling or numbness and a feeling of anxiety or "impending doom", followed by confusion, tremor, convulsions, coma and CPR arrest

– early recognition: discontinue further administration of local anesthetic drugs

– treatment: supportive, sedative/anticonvulsants, cardiopulmonary resuscitation if required

CONTRAINDICATIONSCONTRAINDICATIONS

• Patient refusal: only absolute contraindication

• Conditions that increase the apparent risk of central neuraxial block- Hypovolemia or shock increase the risk of

hypotension- Increased ICP increases the risk of brain

herniation when CSF is lost through the needle, or if a further increase in ICP follows injection of large volumes of solution into the epidural or subarachnoid spaces

- Coagulopathy or thrombocytopenia increase the risk of epidural hematoma

- Sepsis increases the risk of meningitis- Infection at the puncture site increases the risk of

meningitis

• Pre-existing neurologic disease (multiple sclerosis) : considered CI– No evidence to suggest that spinal or

epidural anesthesia alters the course of any preexisting neurologic disease

– Recommendations to avoid RA stem largely from a medicolegal concern that the anesthetic may be incorrectly blamed for any subsequent worsening of the patient’s preexisting condition

SPINAL OR EPIDURAL SPINAL OR EPIDURAL ANESTHESIA?ANESTHESIA?

• Spinal Anesthesia– Less time to

perform– Produces more

rapid onset of better quality sensorimotor block

– Less pain during surgery

SPINAL OR EPIDURAL SPINAL OR EPIDURAL ANESTHESIA?ANESTHESIA?

• Epidural Anesthesia– Lower risk of PDPH– Less hypotension if epinephrine is not

added to the LA– Ability to prolong or extend the block via

an indwelling catheter– Option of using an epidural catheter to

provide postoperative analgesia