Epidural Block

Question 1

What structures are contained within the epidural

space?

Answer 1

Epidural fat, a dense venous plexus (Batson’s plexus), and
segmental arteries are contained within the epidural space.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 787

Question 2

What are the anatomic borders of the epidural

space?

Answer 2

The epidural space extends vertically from the foramen
magnum to the sacral hiatus. Anteriorly, it is bordered by the
posterior longitudinal ligament. Posteriorly, it is bordered by the
vetebral lamina and the ligamentum flavum which adjoins it.
The vertebral pedicles constitute an incomplete lateral border.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 787.

Question 3

With what venous system does the epidural venous
plexus communicate and what is the significance of
this?

Answer 3

Batson’s plexus in the epidural space communicates with the
azygous system, which can cause engorgement of the vessels
during instances of increased abdominal pressure.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 788.

Question 4

What size needle is usually used for an epidural

block?

Answer 4

17 or 18 gauge needles are usually used, which allows a 19 or
20-gauge catheter to be threaded through them.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 45.

Question 5

What is the difference between a Crawford needle

and a Tuohy needle?

Answer 5

A Crawford needle has thinner walls with a traditional point
beveled at about 45 degrees. A Tuohy needle is beveled, but
the end of the needle bends upward.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 45.

Question 6

Why would one choose a Crawford needle over a

Tuohy needle?

Answer 6

The Tuohy needle allows for easier threading of the epidural
catheter when approaching the epidural space perpendicularly.
The bend in the needle tip assists in directing the catheter tip
upward. When using a more acute angle, such as a
paramedian approach, the straight needle tip of the Crawford
needle provides a better angle for threading the catheter
upward.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 45.

Question 7

What is the Loss of Resistance technique for correct

epidural catheter placement?

Answer 7

As the epidural needle reaches the ligamentum flavum, an air or
fluid-filled syringe is connected to the needle. Continuous, mild
pressure is applied to the plunger as the needle is advanced.
As soon as the epidural space is entered, there will a dramatic
loss of resistance on the plunger which verifies the correct
location.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 793.

Question 8

The Loss of Resistance technique can be performed
using either saline or air. Why would you choose
one over the other?

Answer 8

The use of saline has been shown to reduce the incidence of
patchy blockade, postdural puncture headache, and
pneumocephalus. The use of air in the LOR technique has
been associated with subcutaneous emphysema, nerve
compression, and venous air embolism. Some clinicians prefer
to use air when performing a combined spinal-epidural so that
the saline is not confused with CSF when performing the
procedure.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 47.

Question 9

What is the Hanging Drop technique?

Answer 9

The hanging drop technique is used to verify that the epidural
needle has passed through the ligamentum flavum into the
epidural space. A visible drop of fluid is placed on the hub of
the epidural needle. Because the epidural space has a slightly
negative pressure, as the needle enters the epidural space, the
drop of fluid will be sucked into the epidural space.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 793.

Question 10

What is the standard ‘test dose’ for an epidural

anesthetic?

Answer 10

The standard test dose for epidural anesthesia contains 3 mL of
1.5% lidocaine and 1:200,000 epinephrine or 15 mg/mL of
lidocaine and 5 mcg/mL of epinephrine. A test dose contains a
total of 45 mg lidocaine and 15 mcg epinephrine.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 961.

Question 11

Where is the epidural space the largest?

Answer 11

The epidural space is largest in the midline of the lumbar region
at about 5-6 cm wide.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1072-1073.

Question 12

Where are lumbar epidurals usually placed and why?

Answer 12

Lumbar epidurals are typically placed between L2-L3, L3-L4, L4-
L5 and occasionally at the L5-S1 interspace. It is considered
safer to place a lumbar epidural below the level of L1, because
that is where the spinal cord terminates in most adults and the
risk of spinal cord injury is reduced.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 47.

Question 13

What landmark can you use to identify the L1

interspace?

Answer 13

The tip of the 12th rib corresponds with L1.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.

Question 14

What landmark can you use to identify the T3

interspace?

Answer 14

The origin of the scapular spine corresponds with T3.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.

Question 15

What landmark can you use to identify the C7

interspace?

Answer 15

The most protuberant cervical vertebra is at the level of C7.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.

Question 16

What landmark can you use to identify the location of

the T7 interspace?

Answer 16

The tip of the scapula corresponds with T7.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.

Question 17

What is a differential block and how can this be

applied in epidural anesthesia?

Answer 17

A differential, or segmental block occurs when the height at
which motor, sensory, and autonomic block differ. This can be
useful in many circumstances. For example, the administration
of a dilute concentration of local with a small amount of opioid
can be sufficient to block the smaller diameter pain fibers while
sparing the motor fibers. This would allow for pain relief while
allowing the patient to retain motor control.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 959.

Question 18

How does the onset of anesthesia with an epidural

block compare to that of a spinal block?

Answer 18

The onset of anesthesia with an epidural is much slower than
that of a spinal block and usually takes between 10-20 minutes.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 959.

Question 19

Segmental spread of an epidural block is primarily

dependent upon what two factors?

Answer 19

The segmental spread of an epidural is reliant primarily upon
the volume of local anesthetic solution used and the site of
injection. The size of the epidural space increases down the
spinal cord as the cord itself occupies less space. This is in
contrast to spinal anesthesia, which relies more on the dose in
milligrams of the local anesthetic, the baricity of the solution,
and the patient’s position to determine the spread of the
anesthetic.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1091

Question 20

How should the epidural needle bevel be angled if
you are trying to achieve a bilateral block?
Unilateral?

Answer 20

For a bilateral block, the bevel of the needle should be facing
cephalad. For a unilateral block, the bevel should be turned 45
degrees toward the side you wish to block.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 47.

Question 21

Why should you aspirate prior to injecting local

anesthetics via an epidural catheter?

Answer 21

You should gently aspirate prior to each injection to reduce the
risk of intravascular or subarachnoid injection.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 51.

Question 22

What patients have the highest risk for a postdural

puncture headache?

Answer 22

Post-dural puncture headache is most common in postpartum
women in their 30’s.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1085

Question 23

How should you perform an epidural blood patch for

the treatment of postdural puncture headache?

Answer 23

Epidural blood patches should be administered in 15-20 mL
doses (autologous blood) at the level of the dural puncture or 1
level below it.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 969-970.

Question 24

Why is the risk for dural puncture, neural damage,
and vascular injury so much greater when
performing cervical epidurals compared to lumbar
epidurals?

Answer 24

The risk of injury is more dramatic because of the level at which
it could occur (for example, lumbar nerve damage could affect
the lower extremities whereas cervical nerve damage could
result in quadriplegia). It is technically a greater risk because
the epidural space in the lower cervical region is about 20% of
that of the lumbar space. The cervical epidural space is about
1-1.5 cm wide compared to 5-6 cm wide in the lumbar regions.
This provides for a much smaller margin of error.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1072-1073.

Question 25

How does patient position affect the severity of

symptoms of a postdural puncture headache?

Answer 25

One of the hallmark signs of PDPH is that it is aggravated by
sitting or standing and relieved by lying down.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 969-970.

Question 26

How is a paramedian approach for an epidural

performed?

Answer 26

The needle entrance site begins 1 cm lateral to the inferior
border of the spinous process above the interspace desired. It
is then advanced through the subcutaneous tissue and
paraspinous muscles until it strikes the lamina of the inferior
vertebra. The needle is then walked medially and superiorly off
of the lamina until the ligamentum flavum is reached. Once
there, any of the approaches for traversing the ligamentum
flavum without interrupting the dura can be applied.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 793.

Question 27

What is the most common side effect of

postoperative epidural analgesia?

Answer 27

Hypotension, mild sensorimotor changes, and urinary retention
are the most common side effects of epidural local anesthetics.
Pruritus, sedation, and urinary retention are the most common
side effects of epidural opioids.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1308

Question 28

Performing an epidural via the paramedian approach

avoids what ligament?

Answer 28

The paramedian approach avoids the interspinous ligament.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 793.

Question 29

What is the site of action of epidurally administered
local anesthetics? How do drugs administered
epidurally reach their site of action?

Answer 29

Both spinal and epidural anesthetics exert their primary action
on the nerve root. Epidurally administered drugs reach their
destination by coursing along the epidural space and then
diffuse through the meninges and the dural cuff to reach the
nerve root.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1073.

Question 30

While attempting to place an epidural needle, you
get CSF return through the needle. What are your
options?

Answer 30

You should resist the urge to remove the needle immediately.
Instead, place your finger over the hub to stop the flow of CSF.
You can convert the epidural into a combined spinal/epidural or
you can replace the epidural at another location. Many
practitioners will administer the intrathecal analgesic dose
through the epidural needle while it is in the subarachnoid
space and then place an epidural catheter at another interspace.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 55.

Question 31

Does a negative response to an epidural test dose
guarantee that the catheter is within the epidural
space?

Answer 31

No, but it reduces the chance that the catheter tip is within a
blood vessel or the subarachnoid space.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 51

Question 32

How should the timing of low molecular weight
heparin administration be coordinated with the
insertion of an epidural catheter?

Answer 32

If LMWH is planned postoperatively, the epidural catheter
should be removed no sooner than 2 hours before the first
dose. If the patient is already on LMWH, the catheter should be
removed at least 10 hours after the most recent dose and at
least 2 hours before the next dose.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 949.

Question 33

How should you identify the correct placement for a

high thoracic epidural? A mid-thoracic epidural?

Answer 33

The approach for a high thoracic epidural should be made at
the C7-T1 interspace. The C7 spinous process is the most
prominent and allows for easy determination of the C7-T1 level.
A midthoracic approach is typically made using the root of the
scapula, which lies at about T3. The inferior angle of the
scapula roughly approximates T7.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 57.

Question 34

Your first attempt at an epidural for a patient resulted
in a dural puncture. You successfully placed the
epidural catheter at another interspace. What
precautions should you take in administering
medications through the catheter?

Answer 34

Injecting medications through a catheter after creating a dural
puncture at another interspace carries the potential that a
portion of the epidurally administered dose will enter the dural
puncture into the subarachnoid space. This is especially true of
bolus doses. Hydrophilic drugs are more prone to diffusing into
the subarachnoid space than lipophilic drugs. Therefore, you
should exercise extreme caution when injecting large volumes
of local anesthetics or epidural morphine in this situation.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 55.

Question 35

You have administered an epidural anesthetic, but
the block is ‘patchy’ with some dermatome segments
missed. You wish to administer more local
anesthetic to try enhancing the block. How should
you initially re-dose the epidural?

Answer 35

You should administer 20-25% of the original dose administered
about 20-25 minutes after the original dose was administered.
This way, you can ‘deepen’ the block without increasing the
height or spread of the block beyond your intended goal.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 55.

Question 36

You are certain that the epidural needle tip is within
the epidural space, but the epidural catheter will not
advance. What can you try to alleviate this problem?

Answer 36

You can instruct the patient take a deep breath to see if the
catheter advances more easily. It is not recommended that you
rotate the needle while it is inserted as this may increase the
risk for a dural puncture. Also, the injection of saline has not
been shown to be effective in resolving difficulties with catheter
advancement. A technique that has been shown to be effective
is to withdraw the epidural needle several millimeters, then
apply downward pressure on the hub of the needle which
changes the angle of the bevel and may provide an open space
through which to advance the catheter.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 54.

Question 37

You have advanced the epidural catheter beyond the
tip of the epidural needle tip and now need to
reposition the epidural needle to a different
interspace. Should you withdraw the catheter first?

Answer 37

No. Once you have advanced the catheter beyond the tip of the
epidural needle, you must remove them together. Trying to pull
the catheter through the epidural needle may shear the catheter
off inside the patient.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 54.

Question 38

You are trying to advance an epidural catheter
through a Tuohy needle and the catheter will not
advance. What is likely the problem?

Answer 38

It is likely that the epidural needle tip is not within the epidural
space and the needle position should be re-evaluated.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 53.

Question 39

You aspirate clear fluid from an epidural catheter.
How can you determine whether the fluid is
previously injected local anesthetic or CSF?

Answer 39

CSF contains glucose and a glucometer or urine dipstick test
can rapidly determine whether or not the solution is CSF.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 51.

Question 40

You are aspirating an epidural catheter prior to
injection and clear fluid returns very slowly in a ‘stop
and go’ fashion. What should you do?

Answer 40

It is possible that the fluid returning in this manner is either
previously injected saline or local anesthetic, or is cerebrospinal
fluid. It is important to determine the source of the aspirate
before assuming the catheter is in the correct position.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 51.

Question 41

You are aspirating an epidural catheter prior to
injection and clear fluid returns easily. What do you
suspect?

Answer 41

The easy return of clear fluid indicates that the catheter is in the
subarachnoid space and you are aspirating CSF. You should
not inject local anesthetic through the catheter.
Wong, CA. Spinal and Epidural Anesthesia. New York:
McGraw-Hill; 2007: 51.

Question 42

What are the advantages and disadvantages to

adding clonidine to an epidural?

Answer 42

The addition of clonidine to an epidural has been shown to
significantly increase the quality and duration of pain relief. As
it absorbs into the systemic circulation, it can produce
bradycardia, hypotension, and sedation.
Longnecker DE, Newman MF, Brown DL, Zapol WM.
Anesthesiology. 2nd ed. New York: McGraw-Hill; 2012: 1308.