American Society of Regional Anesthesia and Pain Medicine November 2017 - 52

however, they studied the pressure waveform through the catheter,
which may be less accurate. This technique can be performed
quickly with equipment that is already readily available in operating
rooms at low cost and minimal time.
Nerve stimulation via the epidural catheter has proven to be
beneficial in confirmation of catheter placement into the epidural
space. Tsui et al13 demonstrated improvement in catheter
placement confirmation and predicted function. Since that
time, the Tsui Test has been described for use in postoperative
analgesia, pediatric setting, chronic pain, and obstetric anesthesia.
Subsequent studies have verified its high rate of sensitivity and
specificity since its description.7 Advantages include the ability to
determine the spinal level of the epidural tip as well as intrathecal,
subdural, and intravascular detection. One drawback may be that
a specialized catheter is necessary when using bipolar electrical
stimulation. However, the technique described by Tsui et al14 uses
monopolar stimulation, which can be performed with commonly
available epidural catheters. Additionally, patient discomfort should
be considered before performing this technique.
Regional anesthesiologists
are increasingly adept at
the use of ultrasonography.
Therefore, using
ultrasonography to assist
with neuraxial techniques is a
natural progression for many
regionalists. Preprocedural
ultrasound scanning provides reliable and accurate information on
several critical aspects needed for successful epidural placement,
such as the interspace level, the midline of the spine, the window
between spinous processes/laminae, and depth to ligamentum
flavum/dura.15 In 2002, Grau et al16 observed that women who
received labor epidurals with ultrasound assistance had fewer
attempts, more complete analgesia, and improved pain scores as
compared to the LOR-only group.

needle advancement more logistically feasible may dramatically
improve the utility of ultrasonography in varied patient populations.
Finally, the use of fluoroscopy for catheter placement and
confirmation of catheter tip position has demonstrated not only
decreased failure rates but also improved patient outcomes.18 Realtime fluoroscopic guidance allows visualization of the predicted
spread of infusate by examining the pattern of dye spread on
epidurogram. The improvement in catheter tip location with this
technique has been associated with reduced PACU and hospital
length of stay and improved pain scores.18,19 The downside to this
technique is the equipment, financial, and personnel resources
required to use fluoroscopy as well as the risk of radiation
exposure. These limitations have prevented fluoroscopy from
becoming standard practice in the perioperative setting. However,
this modality can be of great benefit in patients for whom epidural
placement is known or anticipated to be difficult.
Additional, novel techniques and devices are being described that
may have potential clinical applications in the future. A real-time,
3D ultrasound rendering
technique with needle
guide has been developed
and is undergoing
preliminary tests in
humans.20 A mobile optical
probe mounted inside a
standard epidural needle
has also been developed
that alarms once the tissue within the epidural space is detected.
This device has thus far been tested only in animals.21 A small
ultrasound transducer, inserted into a Tuohy needle, has been
used in a porcine model to detect dura mater and the epidural
space.22

"The role of additional modalities to
confirm or facilitate epidural placement
may be of notable benefit."

Although most of the published literature thus far has focused
on the obstetric population, there has been an increased use of
ultrasound guidance for thoracic epidural placement. A recent
study evaluating thoracic epidural placement demonstrated no
significant decrease in procedure time, but did report a reduction
in pain scores in the postanesthesia care unit (PACU) and number
of needle puncture sites.17 It is important to note that all patients
studied had a mean age of 58 years and body mass index of 27
kg/m2. Considering the current thoracic data, there may be less
benefit to those with low predicted difficulty. The additional time
and skill required for ultrasound-assisted placement may be
warranted in patients with known or anticipated difficult epidural
placement because of body habitus or spinal abnormalities. Future
advancements making real-time ultrasound visualization of Tuohy

Although traditional methods of thoracic epidural catheter
placement are generally simple and easily taught, the above
modalities can be useful adjuncts. Financial and time constraints
may dictate that some modalities are reserved for especially
difficult cases, but their use should still be considered on a
case-by-case basis. As evidence grows for these techniques in
varied clinical circumstances, certain ones may be adopted as
a standard modality, especially if they are low cost and simple.
In the meantime, having the knowledge and skills to use these
techniques provides the clinician with additional tools when
traditional methods fail, potentially improving patients' analgesia
and outcomes.
REFERENCES
1.

Hermanides J, Hollmann MW, Stevens MF, Lirk P. Failed epidural: causes
and management. Surv Anesthesiol 2013;57:43. doi: 10.1097/01.
sa.0000424242.67406.ab.

American Society of Regional Anesthesia and Pain Medicine
2017

Table of Contents for the Digital Edition of American Society of Regional Anesthesia and Pain Medicine November 2017