Where is the epidural space shallowest?

In some places, the dura may fuse w/ what?

Anteriorly

Dura may in some places fuse with the posterior longitudinal ligament

Where is the epidural space deepest?

How deep?

midline posteriorly

 depth varies

What are the contents of the epidural space?

What is the primary component?

Fat (Primary component)

Venous Plexus (Batsons Plexus)

Segmental Arteries

Lymphatics (laterally)

Primarily in the posterior and lateral epidural space

(not a continuous layer, but little globules of fat)

The general adiposity of the patient

(how fat the pt is)

Describe Batsons Plexus

Are there valves in these veins?

the epidural venous plexus

An extensive network of valveless veins

What does Batson plexus anastomose with?

If your pt experiences an immediate HA while placing an epidural what may be the cause?

Intracranial venous sinuses

Pelvic veins

Azygous System

air in epidural vein the the head per lec

What may dilate the venous plexus and why do I care?

Can this be quantified?

Increased abdominal pressure

or

 a mass compressing the vena cava

Increases the probability of puncturing a vein during epidural placement

Increases the spread of LA d/t decreased effective vol of epidural space

(dilated veins take up more space in epidural sp)

enough variability in dosing that this would be hard to quantify

Near the dural cuff

(laterally)

The angle of the spinous processes

Natural curvatures of the spine

Abnormal curvatures of the spine

Effect of positioning on above

Where is the thickness of the ligamentum flavum greatest?

Where is the depth of the epidural space greatest?

Midline

Midline

Do the curvatures of the spine affect movement of LA with an epidural?

Review:

The cervical and lumbar curves are convex ______.

Where are the high points of these areas?

The thoracic and sacral curves are convex ______.

Where are the low points of these areas?

Although we are not injecting into CSF (and therefore baricity of LA solution not a concern)...

LA in epidural space can still "run off" from lumbar to thoracic area

The cervical and lumbar curves are convex anteriorly.

high points: C5 & L5

The thoracic and sacral curves are convex posteriorly.

low points: T5 & S2

How do HD parameters compare in epidural with epi vs without?

Spinals?

refer to figure in slide 28 (p 945 Barash)

Epidural w/epi: larger decr PVR & MAP, incr CO & HR

Epidural w/out epi: Slight decr PVR & MAP, CO & HR relatively unchanged

Spinals: slight decr PVR & MAP, HR & CO initially incr slightly then decr ~10%

Epidural with epi results in larger decr in PVR & MAP in 1st 15 min or so d/t B2-adrenergic-mediated vasodilation produced by low doses of absorbed epi

also see incr in CO & HR

~ 1 hr after initially given, all start going back to baseline

Epidural w/out epi results in ~ 10% decr PVR & MAP & slight incr in CO & HR, but these go back to ~ baseline (although after ~ 100min decr PVR & incr CO)

Spinals similar to epidurals w/out epi, but MAP stays slightly below baseline & after initial incr HR, HR decr below baseline (<10% below)

 They do not differ much

The differences that do exist are due to the much larger volume and dosage of drug required for epidural anesthesia

Due to the larger volumes and doses given in epidurals, how might narcotic requirements be affected?

How does epidural fentanyl compare to IV?

Local anesthetic blood levels may be adequate to reduce narcotic requirement

Epidural Fentanyl produces a blood level almost equivalent to an IV dose

(sig absorption of epidural fent systemically)

(epidural fentanyl can affect fetus; when baby delivered & is flaccid, prolly needs narcan)

Patient position, more or less significant compared to a spinal?

What should be avoided?

Less significant in determining block height

Avoid extremes of positioning, such as sitting, unless desiring a lower block

If I maintain a patient in the lateral decubitis position after epidural dosing, how will it affect my block?

How does this compare to spinals?

Provides a somewhat better block on the down side

but you still have effects on the up side

effect much less pronounced than w/ spinal anesthesia

(with spinals will have much larger difference between block on down side & up side; baricity will determine which side has greater effect)

What are two main points to be considered in preparation for an epidural?

How does prep and drape of pt for epidural differ from spinals?

Assure this is an appropriate surgery for an epidural

Assure the patient is an acceptable candidate for epidural anesthesia

Prep and drape same for both

(review on slides if needed)

The key element needed for success is...?

What type of needle is used to thread a cath into epidural space?

Position!!!

Touhy

What position is used most frequently for caudal epidural in adults?

In children?

adult: Prone

child: lateral decubitus

I'll just put a pillow under the iliac crest to rotate the pelvis

Legs spread slightly ~20 degrees with toes pointed inward

As in a spinal, which interspaces are we indentifying?

L3-4 or L4-5

No higher than L2-3

How do you inject subQ analgesia?

On what do I base the depth of the injection?

 Same as for spinal:

start near bottom of chosen interspace

create skin wheal of 1% lidocaine w/ 25g or smaller needle

The patients body habitus

Describe the needle insertion for epidural.

What are 2 goals for advancing the needle?

Midline Approach

Nearer the bottom of the interspace

10-15 degree cephalad angle

Anchor styleted needle in ligamentum flavum

Advancing the needle goals is same as in spinal:

absolute control of needle depth

tactile sensation of diff't tissues

-distinction b/n ligament & paraspinous mm, which is entered if you deviate from midline

What are two methods of indentification of the epidural space?

Which is most common?

Hanging drop

Loss of resistance

*Most common

Subatmospheric pressure in epidural space will suck the drop of solution into the needle:

with needle in ligamentum flavum, place a drop of soln w/in hub of needle

when needle advanced into epidural space, soln is sucked in

1. Insert epidural needle into ligamentum flavum with bevel facing laterally (parallel w/ SC) & anchor hand on pt back

2. Attach glass syringe with saline, air, or saline with a small air bubble to needle

3. Slowly advance needle while applying constant, or bouncing pressure on plunger

4. When loss of resistance encountered, inject some of the saline & turn the bevel cephalad or caudad 

When advancing the epidural catheter, what may faciliate advancement?

Catheter should advance _____, without meeting _____.

Injection of air or saline

Catheter should advance easily, without meeting resistance.

Grab the patient by the shoulder and put your foot on the syringe and...

No! Just kidding!

You're in the wrong place

 or

 you're up against something

You must remove the needle and catheter as a unit and start over

(if you try to pull the catheter back thru the needle you can shear off part of the catheter into the pt)

How far do I advance the catheter?

Once the catheter is in position, what do I do with the needle?

How do I know I'm in the right place?

What's one way to ensure my catheter didn't move when I removed the needle?

Miller states 2-3 cm or 4-6 cm for some, but Rons says "pretty far" Hillcrest says 6cm

Needle is withdrawn over the catheter

(be careful not to remove catheter w/ it) 

Hub is attached to the catheter and following aspiration a test dose is given to affirm that you are not intravascular or subarachnoid.

Compare 15 cm mark on catheter with finger or syringe before & after needle removed

(not necessary per Ron)

Ok, so I don't know what the hell I'm doing...where might my catheter be if it's malpositioned?

What are 2 other concerns?

Subarachnoid (numbness w/in 1st 5 min)

Subdural (numbness w/in 5 min)

Intravascular (tachycardia or ringing in ears)

Foraminal (only numb on one side after full dose)

Other concerns:

Septum

Adhesions

(both can prevent fluid in epidural space from moving from one side to another)

(if get any block w/in 1st 5 min after epidural test dose, you are either subarachnoid or subdural)

Benzoin

Mastisol

How do we secure the catheter for long term use?

If we get called back b/c epidural is no longer working, what do we do?

Sterile occlusive dressing

Check that catheter is still in pt & that catheter is still hooked to IV tubing

catheter could've moved in pt, or be in blood vessel

To insure the catheter is not

Intravascular or Subarachnoid

Ringing in the ears

Increased HR >20bpm above baseline

(may not see with pts on beta blockers or may be difficult to determine HR cause with pts in active labor)

Incrementally and only after aspiration

Typically 4ml at a time (hillcrest = 4ml q min)

*Miller says this does not adversely affect the block, height, duration, or density.

What are the steps for caudal placement?

How do we determine correct placement?

What does absence of a midline bulge imply?

What should be done after determining correct placement?

1. Puncture sacrococcygeal membrane at about a

    45 degree angle until bone is contacted

2. Withdraw slightly and redirect needle in a

    shallower plane

3. Advance needle 1-2 cm into the caudal canal

Check for Caudal pressure wave:

Rapidly inject 5ml of saline, while palpating gently over the sacrum

Absence of a midline bulge/pressure wave implies correct, or at least not subcutaneous placement of the needle

apspirate & give test dose

After inserting needle at 45 degree angle...

for males, redirect needle almost flat

for females, redirect needle to 15 degree angle

Subdural locations, incl. close to the spinal cord

gotten close to SC & is now affecting nerve roots

(remember, spinals affect the nerve roots right away, or so we think)

Lidocaine 2%

Mepivacaine 2%

I have intermediate onset, longer duration.

Who am I?

Bupivacaine 0.5-0.75%

(don't use 0.75% for OB or any epidurals d/t cardiotoxicity)

Levobupivacaine 0.5-0.75%

Ropivacaine 0.75 - 1%

2-Chloroprocaine 3%

Onset?

Peak?

Duration?

Prolongation by Epi?

Chloroprocaine

Onset - 2-4 min

Peak - 10-15 min

Duration - 30-60 min

yes 40-60%

Lidocaine 2%

Onset?

Peak?

Duration?

Prolongation by Epi?

Lidocaine 2%

Onset - 2-4min

Peak - 10-15 min

Duration - 45-75 min

yes

Mepivacaine 2%

Onset?

Peak?

Duration?

Prolongation by Epi?

Mepivacaine 2%

Onset - 2-4 min

Peak - 10-15 min

Duration - 50-75

yes

Ropivacaine 0.75-1%

Onset?

Peak?

Duration?

Prolongation by Epi?

Ropivacaine

Onset - 4-6 min

peak - 15-20 min

duration - 60-120 min

Minimal

Levobupivacaine 0.5-0.75%

Onset?

Peak?

Duration?

Prolongation by Epi?

onset - 4-6 min

Peak - 15-20 min

duration - 60-120 min

minimal

What is the most important factor affecting the epidural dose?

Decreased epidural fat content

Less compliant epidural space

Decreased ability of drug to leak out of intervertebral foramina

Studies vary

Some suggest a reduced dosage requirement in pregnancy

Increasing volume at a constant _____, or

increasing volume & dose at a constant _____ increases spread, but in a _______ manner.

Increasing volume at a constant dose, or increasing volume and dose at a constant concentration increases

spread, but in a non-linear manner.

What is the effect of position on epidural dosing?

What does a 30 degree head up position do?

Position has little effect

30 degrees head up improves low-lumbar & sacral analgesia with no decrease in thoracic block height

What are the two schools of thought when dosing a labor epidural?

Which would you add narcotic to?

Establish block with 0.25% Bupivacaine and start an infusion of 0.0625%-0.125% Bupivacaine

(Ron says this is stupid-can cause hypotension & give pt false sense of what to expect from epidural)

or

Establish block with 0.0625%-0.125% Bupivacaine and start and infusion of the same

Most will add a narcotic to either of these

What is the range of concentrations for Bupivacaine & Fentanyl mixture for continuous infusion in labor?

Infusion rates?

Why do we like bupivacaine for labor?

Range from 0.05% -0.125% Bupivacaine

1-5mcg/ml of Fentanyl

Infusion rates vary from 10-18ml/hr

Gives more sensory than motor block, so pt can still push

What is the perineal or delivery dose for a patient who still needs to push near delivery?

Which LAs/concn?

About 10 ml

can give bolus of infusion concn

or

2% 2-Chloroprocaine

or

1% Lidocaine

What is the perineal or delivery dose if the surgeon is planning instrumented delivery?

Which LAs/concn?

10ml

increase conc'n b/c more painful procedure:

3% 2-Chloroprocaine

2% Lidocaine

Unique feature of epidural dosing is that, having given a dose of LA...

After a period of time, subsequent doses may be ineffective in raising block height.

Miller states that instead the block may become more dense (improved quality) but not higher

Epinephrine

Phenylephrine

Why do we add epi to epidural?

Which LAs are affected most?

 Reduces peak plasma levels of local anesthetics

Significant prolongation of:

 Lidocaine

Mepivacaine

2-Chloroprocaine

Only slight prolongation of others

Do we use Phenylephrine often in epidurals?

How does this affect peak plasma levels?

No, rarely used

Lesser effect on reduction of peak plasma levels as compared to epi

What is the dose for Sodium Bicarbonate added to an epidural & why do add it!

When do we see biggest change?

1meq to 10ml local anesthetic

Speeds onset

May improve density of block

biggest improvement w/ LAs prepackaged w/ epi b/c these have lower pH

What do you do prior to bolus dosing an epidural catheter?

Why?

Aspirate

A catheter can migrate into a blood vessel or the subarachnoid space

Do I need to aspirate prior to a bolus dose if I have an infusion running?

Why?

Do we do a test dose also?

Yes!

It may be running at a low enough level that intravascular injection goes unnoticed

A test dose may be of limited usefulness if significant block already established

Appropriate for planned surgery?

Patient refusal

Infection at site/sepsis

Pre-existing neurologic disease

Increased intracranial pressure

Severe hypovolemia

(same as for spinal)

Must consider the timing of removal in conjunction with anitcoagulant dosing

Miller (p1634) states removal of spinal/epidural catheters used for postop analgesia should take place 10-12h after last dose, w/ subsequent dosing at least 2 hours after

An adequate test dose

Incremental injection of the LA solution

Inhibition of inhibitory neurons in cortex

allows for facilitory neurons to discharge in unopposed fashion producing CNS excitation

After intravascular injection what occurs at higher concentrations r/t CNS?

Why?

CNS depression

Due to inhibition of both inhibitory and excitatory pathways

Ropivacaine and Levobupivacaine

Lower cardiotoxic potential

Test dose

Incremental injection

BP & HR support

Support of ventilation, intubation as needed

Rate of back pain with a spinal?

W/ epidural?

11%

30%

Needle trauma

Local anesthetic irritation

Ligamentous strain

How often does PDPHA occur following dural puncture with a large diameter epidural needle?

In which pts?

What is important to try and prevent this?

Occurs in up to 50% of young patients

Orientation of the needle bevel-should be parallel to SC

What is the definitive trtmt of PDPHA?

Typically, PDPHA resolves in ____ days w/ conservative trtmt, including what 3 things?

epidural blood patch

several days

bed rest, analgesics, caffeine containing fluids

What are possible etiologies of neurologic injury?

How often does it happen?

Direct needle trauma

Vascular injury with subsequent neural ischemic insult

Epidural hematoma

Extremely rare, but potentially devastating results

Is an epidural hematoma a big deal?

What is key to good outcome?

What can make it worse?

Yes-Its a neurosurgical emergency

Early detection is key to good outcome

Outcome significantly worse if treatment delayed more than 8 hours

Possibly not quite as safe due to lack of patient feedback

Removes the potential of the patient moving

Definitely a liability exposure

Maybe:

Meningeal hole made by the spinal needle may allow dangerously high concentrations of subsequently administered epidural drugs to reach the subarachnoid space

anecdotal case reports & in vitro animal studies suggest that this may be a legitimate concern

Tell RN to put pt back into the position in which the epidural was placed and try again

Probably best to just go to pt yourself cause those dang RNs don't know what they're doing!! (j/k :))

If that doesn't work, send pt for MRI

sterile technique

size & type needle

technique used (loss of resistance)

# attempts

depth of catheter

aspiration

test dose

secured catheter

position of pt (L uterine displacement for pregnant pt)

pt tolerance

lot #s/exp date of meds