epidural anesthesia vc07

7/30/2019 Epidural Anesthesia Vc07

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Epidural Anesthesia

Vincent Conte, MD

Associate Clinical Professor

Nurse Anesthesia Program

FIU College of Nursing


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Epidural Anesthesia

Presentation divided into two sections:

1) Anatomy and Physiology2) Techniques


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Epidural Anesthesia

A Neuraxial technique that offers a wider rangeof applications than a Spinal Anesthetic

An Epidural block can be performed at the

Lumbar, Thoracic, Cervical and Caudal level Wide use of applications; Operative anesthesia,

Obstetric Anesthesia & Analgesia, Postop paincontrol and Chronic Pain Management

It can be used as a Single Shot or with acatheter that allows intermittent boluses or aContinuous Infusion


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Anatomy

The Epidural space surrounds the DuraMater posterior, laterally and anteriorly

Nerve roots travel in this space as theyexit the spinal cord laterally

They then exit the foramen and travelperipherally to become peripheral nervescarrying both afferent and efferentpathways


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Anatomy

Other contents of the Epidural spaceinclude:

1) Fatty connective tissue

2) Lymphatics

3) Venous plexus (Batsons)

4) Septa and Connective tissue bands


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Physiology

Local anesthetics or other solutionsinjected into the epidural space (steroids,narcotics) spread anatomically

Horizontal spread is to the region of thedural cuffs with diffusion into the CSF andleakage through the intervertebralforamen into paravertebral spaces

Longitudinal spread is preferentiallycephalad in direction


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Physiology

Possible sites of anesthetic actioninclude:

1) Paravertebral nerve roots

2) Intradural spinal roots

3) Dorsal and Ventral spinal roots

4) Dorsal root ganglia

5) The Spinal Cord

6) The Brain itself (by diffusion)


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Physiology

Initial blockade is PROBABLY a result ofanesthetic blockade at the spinal roots withinthe dural sleeves

The Dural Cuffs or Sleeves have a proliferation

of arachnoid villi and granulations thateffectively reduce the THICKNESS of the duramater facilitating rapid diffusion of the LA fromthe Epidural space, through the Dura and intothe CSF surrounding the nerve roots

Then the local anesthetic diffuses into the nerveroot itself, producing anesthesia to thatparticular dermatome


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Physiology

Because Epidural anesthesia is DIFFUSIONdependent, relatively LARGE volumes ofLA are needed to achieve a block thatspans several dermatomes

The block ONLY goes as high or low asyou regulate it (by volume)

Its not like a Spinal which is EVERYTHINGdistal to the level of the block; it is aDIFFERENTIAL block dependent on thevolume and site of injection


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Advantages

Consequently, Epidural techniques have theadvantage of better control of level (and alsoof sympathetic blockade)

Epidural techniques allow for the placement ofa continuous catheter which is especially usefulfor:

1) Cases of unpredictable duration

2) Prolonged postoperative analgesia3) Chronic pain control

4) Obstetric Analgesia & Anesthesia


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Spread of Anesthesia

To be able to choose the most appropriateanesthetic dose, concentration and volume ofLA, the anesthetist must be familiar with the

variables that affect spread and duration ofEpidural Anesthesia

The variables are more numerous than those ofspinal anesthesia and Baricity plays a VERY

small factor when dealing with Epidurals,whereas in a Spinal, baricity is a KEY factor inspread and distribution of the block


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Spread of Anesthesia

The factors that affect the level of the Epidural blockare:

1) Injection Site

2) Dose

3) Volume4) Concentration

5) Position

6) Age

7) Height and Weight (?)

8) Pregnancy (?)

9) Speed of injection (?)


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Injection Site

Caudal epidural blocks are largelyrestricted to sacral and LOW lumbardermatomes

Thoracic levels can be reached by thecaudal approach only if large volumes(30cc) are given, and then the block is

patchy at best because of the distancethat the anesthetic has to travel


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Injection Site

Lumbar local anesthetic injections of 10cctend to spread caudad to include all thesacral dermatomes

Lumbar injections of 20cc volumesproduce much better quality sacral blocksand can also extend cranially to include

the midthoracic levels


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Injection Site

Thoracic injections tend to produce a symmetricsegmental band of anesthesia with minimallumbar spread

When using a thoracic approach, it is prudent to

decrease your volume by about 30-50% toprevent cranially spread

It is generally not feasible to produce surgicalanesthesia in the low lumbar or sacral nerve

distributions when using thoracic injection sites Thoracic injection sites are ideally suited for

procedures of the chest and upper abdomen orfor relief of post-op thoracotomy pain with acatheter being placed for continuous infusions


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Dose, Volume & Concentration

Within the range typically used for surgicalanesthesia, drug CONCENTRATION isrelatively unimportant in determining

block spread

DOSE & VOLUME, however, are importantvariables in determining both spread and

quality of the Epidural block obtained


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So a small volume of a more concentratedLA will produce a very limited BUT verystrong block

But take the same DOSE and double thevolume, the spread will increase BUT thestrength of the block may not be as

intense


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NOTE: The increase in block level IS NOT indirect proportion to the volume increase.Doubling the volume WILL NOT double the block

spread. It is a NON-linear relationship anddoubling the volume will only increase the levelabout 1/3-1/2 the original number of segments

The same relationship exists with DOSE;

doubling the dose will usually only increase thelevel of block the same 1/3-1/2 of the originalnumber of segments blocked


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Recommended amounts of LA differ as towhich level is being injected:

Cervical/Thoracic doses are 0.7 to 1cc persegment with an initial volume of 10cc

Lumbar level doses are 1.25 1.5cc persegment with an initial volume of 15-20cc

This is due to the narrowing of the spinalcanal as it progresses cranially

C t ti d Diff ti l


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Concentration and DifferentialBlock

Using a lower concentration anestheticcan sometimes give you a differentialblock

The lower concentration means the doseis lower and there is less LA to penetratethe nerve roots so the block acts more

peripherally on the nerves, differentiallyblocking sensory and pain fibers overlarger muscle fibers in the center of thenerves


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Concentration and DifferentialBlock

An example of this is used in Obstetrics:

Bupivicaine 0.25%, 20cc, usually ONLY provides asensory block but leaves the motor fibers intactso the patient can push when needed to

If Bupivicaine 0.5% is given with the samevolume, then a sensory as well as motor block isobtained, paralyzing the muscles at the levels of

the block so NO pushing is going to be possible There is quite a bit of individual sensitivity and

some people may end up with a purely sensoryblock while others may end up with significant

muscle weakness or paralysis; (ooooppps!!)


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Position

Some people feel that the Lateral positionis the preferred position to optimizespread

Others feel that the sitting position ispreferred due to anatomical advantages

Studies have shown small to NO

differences in spread of block whencomparing the two positions; its yourpreference which one to use


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Age

Most (but NOT all) studies that haveexamined the effect of age on Epiduralblocks have demonstrated a greater

spread in older patients This is thought to be related to a less

compliant epidural space and Dura Mater

Even so, the clinical effect is usually ATMOST an increase of no more than threeor four dermatomes


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Height and Weight

The correlation between patient Height orWeight and spread of epidural block isvery weak at best and seems to have no

clinical significance The only instance where it may have an

effect is in EXTREMELY TALL people(greater than 66) or in EXTREMELYSHORT (less than 410) or in MORBIDLYobese patients


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Pregnancy

Studies examining the effect of pregnancyon spread of Epidural blocks areconflicting

Some have shown a greater spread atTERM and early in pregnancy

Other studies have shown no significant

differences in level of spread betweenpregnant and non-pregnant patients

?????????????


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Speed of Injection

Some feel that a rapid injection will increase thelevel of spread or decrease the time it takes forthe block to set

This has NEVER been shown to make anydifference in either

Drugs should, in fact, be injected SLOWLY toavoid rapid increases in CSF pressure, headache

and increased intracranial pressures Also, incremental bolus vs. slow, steady injection

has shown NO difference in level of spread inmultiple studies


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Speed of Injection

All solutions should be injected inincrements of 3-5cc every 3 minutes andtitrated to the desired anesthetic level

If a catheter has been placed and you areinjecting through the catheter, then thecatheter needs to be aspirated prior to

every injection to show no CSF is present


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Speed of Injection

This gradual administration of medication slowsthe rate of onset of the anesthetic level andcontrols the development of the sympatheticblockade

This is an advantage that you have with anEpidural that you DO NOT have with a Spinal

The Spinal is ALL or none, whereas the Epiduralcan be brought up gradually, slowing whateverhypotensive response you may have to a moremanageable level (and saving you an extra pairof pants!!)


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Onset of Blockade

The onset of an epidural block can usually bedetected within 5 minutes in the dermatomesimmediately surrounding the injection site

The time to PEAK effect differs somewhatamong different LAs

Shorter acting drugs usually reach theirmaximum spread in 15-20 minutes

Longer acting LAs usually reach their maximumspread in 20-25 minutes

Increasing the DOSE of LA SPEEDS the onset ofboth motor and sensory block


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Duration of Block

The DURATION of the Epidural blockdepends on:

1) The LA itself

2) Dose given

3) Patient age

4) Use of Adrenergic Agonists


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Local Anesthetics & Duration

Your choice of LA is the most importantfactor in determining DURATION of theblock

Chlorprocaine is shortest, Lidocaine &Mepivicaine are intermediate andBupivicaine and Ropivicaine produce the

longest lasting Epidural blocks


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LAs & Duration

Back to the differential block topic:

ETIDOCAINE is a long acting agent that hasa profound muscle relaxation effect but aweak sensory effect, so you would end upwith a paralyzed patient in severe pain; ithas been almost completely eliminated

from use as a result of this differentialblockade


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LAs and Duration

On the flip side, BUPIVICAINE is theopposite of Etidocaine

In lower doses (concentrations)BUPIVICAINE seems to have a preferentialsensory block with minimal motor effect

That is why it is an ideal drug for Obstetric

ANALGESIA during labor, eliminating painwhile preserving muscle function


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Dose and Age

DOSE: Increasing the DOSE of a LAresults in increased duration AND densityof the block

AGE: There are conflicting studies, but themajority seem to show a longer durationof action in the elderly population. The

exact reason is unknown and more studiesneed to be performed

Ad i A t d


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Adrenergic Agents andDuration

Epinephrine in a concentration of 5micrograms/cc (1:200,000) is the most commonadrenergic agent added to epidural LAs

It has been shown to prolong the blocks ofLidocaine and Mepivicaine by as much as 80%

Epinephrine has been shown NOT to significantlyprolong the duration of anesthesia when added

to concentrated solutions of Bupivicaine andRopivicaine used for surgical anesthesia

Ad i A t d


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Adrenergic Agents andDuration

However, when added to more diluteconcentrations of Bupivicaine, as used for OB

Analgesia, it has been shown to increase the

duration AND quality of the block The mechanism proposed, although never

proven, is that through vasoconstriction, it slowsthe systemic absorption and elimination of the

LA Why it does not work with higher concentrations

of Bupivicaine and Ropivicaine is not clearlyunderstood


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A & P Conclusion

The extent and duration of both SpinalAND Epidural blocks are influenced by anumber of variables, some of which are

under the control of the anesthetist Understanding the impact of these

variables will allow the anesthetist to

select the most appropriate drug and dosefor any given clinical situation


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A & P Conclusion

HOWEVER, even the most experiencedanesthetist will STILL have blocks that arenot adequate or may fail completely

The frequency of failed blocks can be keptto a minimum if the clinician aims for ablock that is a little higher and a little

longer than would ideally be used for thegiven procedure


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A & P Conclusion

REMEMBER, it is often easier to deal witha block that is too high or too long than toattempt to cover up for a block that is too

low or not dense enough Its always better to have a little more

than a little less, especially with Regional

Anesthesia


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Break Time!!


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Technique

Patient preparation and positioning aresimilar to a Spinal Anesthetic

Either the sitting or lateral decubitus

positions can be used

Emergency equipment and monitorsshould be immediately available and you

need to be prepared to use it if any thinggoes wrong


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Technique

The most commonly performed Epidural isa Lumbar Epidural, followed by a Caudal,then Thoracic and finally Cervical

Today most high thoracic and cervicalepidurals are performed underflouroscopic guidance by pain specialists

as it takes a greater level of skill tosuccessfully perform those procedures


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Technique

As you can see in the following diagram,the angles of approach for the variouslevels are markedly different

The Lumbar region is at or greater than90 degrees to the skin

The Thoracic is at a much more acuteangle due to the anatomical arrangementof the Thoracic Spinous Processes

Finally the Cervical is at an angle inbetween the previous two


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Technique

The Lumbar region is by far the easiest due to:

1) The angle of the Spinous processes

2) The larger spaces BETWEEN adjacent spinous

processes3) Easily identifiable location by using easy to find

landmarks (Iliac crests)

4) Width of epidural space is greatest at this levelas well so if you are a little off the mark, youstill stand a good chance of finding it


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Technique

The Epidural is most often performed with a 16,17 or 18 gauge needle with a BLUNTED tipdesigned to facilitate passage of a catheter into

the epidural space at the beginning or end ofthe procedure

The blunted tip is also designed specially toAVOID puncture of the dura and if it comes in

contact with the Dura, the lack of a sharp pointwill hopefully just inwardly push the durawithout puncturing it


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Technique

The procedure is begun by identifying youranatomical landmarks and locating your plannedinterspace of insertion

Then the patient is positioned similar to that of aSpinal Anesthetic

A sterile prep is performed with the plannedinsertion point at the center of both the prepped

area and in the middle of the special hole in thedrape that is provided in the kit


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Technique

Local anesthetic (usually Lido 1% plain) isinjected at the planned insertion site and a skinwheal is raised with an injection of 1-2 cc of

local with the 25g skin needle (see kit) Then some people change local needles and

place the 22g needle on the local syringe, and inthe center of the skin wheal, go deeper along

the planned injection tract, injecting slowly asthey penetrate deeper into the subcutaneoustissue


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Needle Stabilization

Firmly place the BACK of your non-dominanthand against the patients skin and below theepidural needle

Then grasp the needle and eventually the hub

once the epidural space is found between yourthumb and index finger of your non-dominanthand as it stays in contact with the patientsback (the Bromage Grip)

This stabilizes the needle and prevents anyunwanted movement either in or out which isespecially critical once you find the Epiduralspace


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Technique

The Epidural needle is place bevel up andintroduced into the skin

It is passed slowly through the Supraspinous

ligament and seated in the InterspinousLigament before the stylet is removed

You can tell that the needle is seated in theInterspinous ligament by letting go of the

needle; it should still be supported in the sameposition, not drop down


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Technique

After the stylet is removed, the needle is slowlyadvanced using the Loss of Resistancetechnique

The LOR syringe is typically made of glass and is

filled with either 3-4cc of air, normal saline, or amixture of saline and air As the syringe/needle combo is advanced,

pressure is applied to the plunger of the syringeby Bouncing or intermittently applyingpressure to the plunger

The pattern is move-bounce-move-bounce-move-bounce until LOR is obtained


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Technique

The syringe/needle combo should only bemoved 0.5-1cm at a time and then tested forresistance or LOR

The syringe/needle combo is advanced by

applying pressure to the NEEDLE and not thesyringe As the needle passes through the Ligamentum

Flavum, resistance increases and you may feel adistinct pop as you pass through it

Once you pass through the LF, you willexperience an immediate LOR and then the tipof the needle will be in the Epidural Space


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Technique

In younger patients like you mayencounter in Obstetrics, there may not bea distinct pop of the LF, just a sudden

loss of resistance Once the Epidural space is reached, pass

your stylet through the needle to makesure there are no tissue plugs possibly

blocking the flow of CSF with aninadvertent Dural puncture

T h i


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Technique

Once it is determined that your needle tipis in the Epidural space, begin first byinjecting a TEST dose of 3cc of LA

containing Epi (Lido 1.5% w/Epi) If you are intravascular, you will see an

increase in heart rate within 30 seconds

It is also important to question the patientafter the injection of your test dose

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Technique

The questions asked should be aimed atdetermining if you may have inadvertentlyobtained a dural puncture or are possible

injecting directly into the vascular system Besides the tachycardia, with an

Intravascular injection, the patient mayexperience a ringing or buzzing in the

ears, a metallic taste in the mouth orcircumoral numbness

T h i


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Technique

If you happen to have gotten a duralpuncture by accident, the test dose shouldproduce numbness and/or weakness or a

pins and needles sensation in the lowerextremities

This can take up to three minutes tooccur, so you need to wait at least three

minutes before continuing your injectionof LA

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Technique

At this point, techniques and opinionsdiffer as to whether to pass a catheter andinject your total dose via the catheter or

inject your total dose through the needleand then insert the catheter

The catheter first crowd feels that it isbetter because you can slowly raise your

level of anesthesia having better controland less incidence of sympathetic block


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Technique

Regardless of which technique is used, asyou pass the catheter, the patient shouldbe warned that at that moment they may

feel an electric shock or a feeling likethey hit their funny bone

This is caused by the cath tip brushing up

against a nerve root or two as it is passedinto the epidural space

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Technique

As you pass the catheter, you may initiallyfeel resistance at the tip of the needle

A slightly stronger push may be needed

and then you will feel the resistance dropand the catheter will thread smoothly

It should be inserted between 3-5cm and

no more (3-5 little black lines)


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CAUTION


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CAUTION

NEVERpull the catheter back throughthe needle once it has been inserted

It is possible to catch the catheter on theneedle tip and shear or cut the tip off

Then it becomes a permanent new

addition to the epidural space and will bethere for the rest of the patients life!!!!

Caudal Anesthesia


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Caudal Anesthesia

An Epidural technique used for anorectalsurgery in adults

Also one of the most commonly done

regional techniques in pediatric patients Technique is the same for both patient

populations

Difference lies of course with size ofequipment and dosage of anesthesia

Caudal Anesthesia


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Caudal Anesthesia

Caudal anesthesia involves needle orcatheter penetration of the SacrococcygealLigament covering the Sacral Hiatus

The Hiatus is created by the unfused S4and S5 lamina

The Hiatus can be felt as a groove or

notch above the coccyx and between twobony prominences, the Sacral Cornua


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Caudal Anesthesia


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Caudal Anesthesia

The Posterior Superior Iliac Spines and theSacral Hiatus form a triangle (see photo)

The patient is placed either prone or in lateraldecubitus

A Sterile prep is done similar to an epidural andthe landmarks are again palpated A needle or catheter is inserted at a 45 degree

angle to the skin until a pop is felt

Then the angle of the needle is dropped downand advanced, aspirating for blood or CSF every1-2cm


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Caudal Anesthesia


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Caudal Anesthesia

Some clinicians recommend test dosing aswith other techniques, while most simplyrely on incremental dosing with frequent

aspirations Repeated injections can be given or a

catheter can be placed for boluses or a

continuous infusion

Caudal Anesthesia


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Caudal Anesthesia

For adults undergoing anorectal procedures,caudal anesthesia can provide dense sacralsensory blockade with limited cephalad spread

A dose of 15-20cc of 1.5-2.0% Lidocaine with orw/o epi is usually effective

This technique should be avoided in patientswith Pilonidal cysts because the needle may pass

through the cyst track and introduce bacteriainto the epidural space and lead to infection andabscess formation


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Conversion for C-Section


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Conversion for C-Section

A clinical situation that you will be faced with isone in which the patient has an Epidural in placefor labor and is receiving Bupivicaine 0.125 -0.0625% infusion or periodic Bupivicaine 0.25%boluses and now has to be converted to a moreintense level of anesthesia for a C-section

The normal Epidural dose of Lidocaine 2% w/epi

for a C-section is 15-18cc WITHOUT an epiduralin place

Conversion for C-section


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How much do you give if a Labor epiduralis in place to avoid a high block withrespiratory compromise?????

Opinions vary as much as there areanesthetists!!!

Some say that with a GOOD labor Epiduralin place, no more that 12cc should be

given; others say no more than 10cc andsome go as high as 15cc


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Unfortunately, depending on the answer

to those questions, your dose may varyfrom a low of 10cc to a max normal doseof 15-18cc

Only clinical experience can be called uponin this situation so until you feelcomfortable with your decision, always

consult with your attending or anotherCRNA with greater clinical experience thanyou

Conclusion


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Conclusion

Spinal and Epidural anesthesia each haveadvantages and disadvantages that may makeone or the other technique better suited to aparticular patient or procedure

Studies comparing both techniques haveconsistently found that Spinal anesthesia takesless time to perform, produces more rapid onset

of both sensory and motor block and isassociated with less pain during surgery

Conclusion


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Conclusion

Despite these important advantages,Epidural anesthesia offers advantages, too

Chief among them are the lower risk of

PDPH, less hypotension, the ability toprolong or extend the block using anindwelling catheter, and options to use the

same catheter for postoperative analgesia


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epidural anesthesia vc07

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