Epidural Block Flashcards
What structures are contained within the epidural
space?
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
What are the anatomic borders of the epidural
space?
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.
With what venous system does the epidural venous
plexus communicate and what is the significance of
this?
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.
What size needle is usually used for an epidural
block?
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.
What is the difference between a Crawford needle
and a Tuohy needle?
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.
Why would one choose a Crawford needle over a
Tuohy needle?
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.
What is the Loss of Resistance technique for correct
epidural catheter placement?
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.
The Loss of Resistance technique can be performed
using either saline or air. Why would you choose
one over the other?
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.
What is the Hanging Drop technique?
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.
What is the standard ‘test dose’ for an epidural
anesthetic?
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.
Where is the epidural space the largest?
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.
Where are lumbar epidurals usually placed and why?
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.
What landmark can you use to identify the L1
interspace?
The tip of the 12th rib corresponds with L1.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.
What landmark can you use to identify the T3
interspace?
The origin of the scapular spine corresponds with T3.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.
What landmark can you use to identify the C7
interspace?
The most protuberant cervical vertebra is at the level of C7.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.
What landmark can you use to identify the location of
the T7 interspace?
The tip of the scapula corresponds with T7.
Lee CY. Manual of Anesthesiology. Singapore: McGraw-Hill;
2006: 402.
What is a differential block and how can this be
applied in epidural anesthesia?
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.
How does the onset of anesthesia with an epidural
block compare to that of a spinal block?
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.
Segmental spread of an epidural block is primarily
dependent upon what two factors?
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
How should the epidural needle bevel be angled if
you are trying to achieve a bilateral block?
Unilateral?
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.
Why should you aspirate prior to injecting local
anesthetics via an epidural catheter?
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.
What patients have the highest risk for a postdural
puncture headache?
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
How should you perform an epidural blood patch for
the treatment of postdural puncture headache?
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.
Why is the risk for dural puncture, neural damage,
and vascular injury so much greater when
performing cervical epidurals compared to lumbar
epidurals?
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.
