Flashcards in Chapter 72 Central and Peripheral Neurolysis Deck (67):
used for the treatment of trigeminal neuralgia.
Phenol and ethyl alcohol
the only two agents commonly used in the epidural or intrathecal
space, as well as for sympathetic plexus neurolysis.
Chemical and surgical neurolysis is primarily limited to
patients with pain associated with terminal malignancies. These procedures provide the most benefit in the oncology patients in whom more conservative measures were unsuccessful, possessed too high a side effect burden, or
unable to be performed
In patients in extremis, neurolysis represents a
palliative measure to provide pain relief while
maintaining the patient’s ability to interact with family and friends in their final days to months of life. This can be
preferable to systemically delivered opioids, which may
interfere with the patient’s mental status enough to diminish
meaningful communication with family and friends.
Neurolysis is an alternative to allow patients the ability to
control their pain with less systemic medication,
significantly improving their quality of life.
Intrathecal Neurolysis: Indications for Neurolytic
Intractable cancer pain (advanced or terminal malignancy)
Failure of medical and interventional analgesic therapy
Intolerable side effects of current therapy
Pain restricted to one to four dermatomal levels
Pain located in the trunk, thorax, abdomen
Primary somatic pain mechanism
Absence of intraspinal tumor spread
Effective analgesia with local anesthetic block
Informed consent of patient
Although neurolysis can provide analgesia in the dermatomal distribution affected by the block, it will not necessarily
provide pain relief from
an expanding tumor or new metastasis. In addition, the effects of this therapy can be temporary, and will diminish over time, requiring re- administration
of the neurolytic agent
Adverse Effects of Neurolysis
limb weakness and loss of bowel or bladder tone
With neurolysis patients
with complaints of neuropathic pain will not get the desired results compared to those with
visceral or somatic pain
Due to the nature of neurolytic administration, it is ideal
unilateral pain in the trunk and focused
to a few adjacent dermatomes. However, in the presence of an intraspinal tumor, the effectiveness of these techniques will decrease, making these patients unsuitable
candidates. Neuraxial neurolytic therapy is ideal for patients
with advanced or terminal malignancy and unilateral somatic
Once a definitive plan is established, informed
consent should be explained in detail to the patient, outlining
all the risks associated with the particular procedure. A thorough neurologic examination before any invasive
techniques are attempted is vital not only for assessing the
effectiveness, but it can provide a baseline assessment in
the event of any potential complications.
Before any neurolytic agents are used, it is advisable to perform a
diagnostic blockade with
a local anesthetic that reproduces the planned intervention. This diagnostic maneuver helps to confirm needle placement and can provide information
about the level of effectiveness of the neurolysis.
The choice of neurolytic
agent is based on
the location of needle placement, the ability of the patient to get in the required position, and the volume of injectate required
may play a role in determining which neurolytic agent to use
for the patient.
Phenol vs. Ethanol
Phenol is a hyperbaric agent that would be
more appropriate for pelvic and saddle blocks compared with a hypobaric agent such as ethanol.
Ethyl alcohol injections perineurally are associated with
burning dysesthesias running along the course of the nerve. To alleviate this known effect, most practitioners inject a local
anesthetic preceding the use of ethyl alcohol.
The neurolytic action of alcohol is produced by
the extraction of
neural cholesterol, phospholipids, and cerebrosides, and the precipitation of mucopeptides. These actions result in sclerosis of the nerve fibers and myelin sheath, leading to demyelination
During neurolytic action of alcohol the basal lamina of the Schwann cell sheath remains intact, allowing for
new Schwann cell growth, thereby providing the framework for subsequent
nerve fiber growth. This framework encourages the regeneration of axons, but only if the cell bodies of these nerves are not completely destroyed.
Areas of demyelination can be seen in
posterior columns, Lissauer’s tract, and the dorsal root,
followed by Wallerian degeneration to the dorsal horn.
Intrathecal alcohol injection results in
rapid uptake of alcohol and variable injury to the surface of the spinal cord. Ethyl alcohol is quickly absorbed from the cerebrospinal fluid (CSF) so that only 10% of the initial dose
remains in the CSF after 10 min and only 4% after 30 min.
The rapid spread from the injection site of Intrathecal alcohol means
larger volumes are required than for phenol, which in
turn may result in local tissue damage
The use of ethanol as a neurolytic agent has been associated with
a disulfiram-like effect, known as acetaldehyde syndrome. The patients experienced flushing, hypotension,
tachycardia, and diaphoresis within 15 min of alcohol administration.
medications that may cause disulfiram-like effects after
peripheral neurolytic blocks with alcohol, such as
beta-lactams, metronidazole, tolbutamide,
chlorpropamide, and disulfiram.
specific gravity of Ethyl alcohol and CSF
Ethyl alcohol has a
specific gravity of less than 0.8, and CSF has a specific
gravity of slightly greater than 1.0. Within the CSF, alcohol
is hypobaric and will move against gravity, “floating”
upward. Therefore, positioning of the patient is an
extremely important factor to consider when planning
The administration of ethanol for the purpose of neurolysis can have catastrophic consequences.
It has been associated with
both transient and permanent paraplegia in both celiac plexus and intrathecal blocks. It has been postulated that these effects are secondary to vasospasm of the spinal arteries by the direct action of alcohol.
Characteristics of Neurolytic Agents: Alcohol
Physical properties: Low water solubility
Stability at room temperature: Unstable
Relative to cerebral spinal fluid: Hypobaric
Patient position: Lateral
Added tilt: Semiprone
Painful side: Uppermost
Injection sensation: Burning pain
Onset of neurolysis: Immediate
Cerebrospinal fluid uptake ends: 30 min
Full effect: 3-5 days
Characteristics of Neurolytic Agents: Phenol
Physical properties: Absorbs water on air exposure
Stability at room temperature: stable
Concentration: 4-7%. 4%-10% are typically used for neurolysis
Relative to cerebral spinal fluid: Hyperbaric
Patient position: Lateral
Added tilt: Semisupine
Painful side: Most dependent
Injection sensation: Painless, warm feeling
Onset of neurolysis: Delayed (15 min)
Cerebrospinal fluid uptake ends: 15mins
Full effect: 1 day
A neurolytic intrathecal block should be performed at the
the target dorsal root leaves the spinal cord, and not at the level where it passes through the intervertebral foramen. The latter is not recommended due to mismatch of the spinal cord level and vertebral bone level
(especially as one progresses from high thoracic levels to
An accurate determination of the level to be blocked should be evaluated according to
dermatome and sclerotome charts, as well as selective local anesthetic blockade
the patient should be positioned laterally so that the
rootlets (dorsal root entry zone [DREZ]) are above the injection site. This positioning is necessary given that alcohol will float in the CSF due to its greater specific gravity that renders it hypobaric
The patient should also be turned 45 degrees
toward the prone position. This will
raise the DREZ (dorsal root entry zone) horizontally so it will be superior to the ventral nerve rootlets.
After proper patient positioning, correct needle
depth must be obtained. A short, beveled needle is placed
slowly into the predetermined location until arriving at the epidural space. This is best-confirmed using loss of resistance to air. After ascertaining that the epidural space has been reached, the
needle should be advanced slowly while aspirating continuously until it reaches the intrathecal space. Once the
needle is in the intrathecal space, adjust the bevel so it
is anterior to the arachnoid mater. placement may be verified with radiographic imaging and contrast
dye administration. The practitioner may then inject
the alcohol, or it may be preceded by a low-volume injection of local anesthetic.
Drug and Dose
Using a tuberculin syringe, the
alcohol is injected in 0.1-ml increments, with at least
60 seconds (preferably 90 sec) between repeat administrations. Total alcohol volume should not exceed 0.5 to 0.7 ml.
After injection, the patient should remain
in the same position for 15 to 30 min. This immobilization
allows the alcohol to exert its maximal effect at the desired
location, with minimal spread to adjacent levels. After the
30-min time period, a neurologic examination should be performed.
Three to 5 days after the alcohol injection, the
patient’s pain should be evaluated to assess
effectiveness of the technique and determine whether repeat injections are required.
a benzene ring with one hydroxyl group substituted
for a hydrogen atom.
Phenol in water and at room temperature
Phenol is poorly soluble
in water and, at room temperature, forms only a
6.7% aqueous solution. Consequently, phenol is frequently prepared with contrast dyes and either sterile
water, saline or glycerin
When phenol is exposed to
room air, it undergoes
oxidation and turns a reddish
color; however, it has a shelf life of approximately 1 year
if refrigerated and shielded from light exposure.
When phenol is prepared with glycerin
it has limited spread,
and, hence, injections are well localized.
Unlike alcohol, phenol injection
has an initial local anesthetic
effect. It is not associated with localized burning,
but instead, creates a sensation of warmth and
Preparations of phenol in glycerin
When phenol is prepared in glycerin, it has a specific
gravity of 1.25, making it hyperbaric. Preparations of
phenol in glycerin are highly viscous, which may make
administration through a spinal needle difficult. Warming
the injectate in a warm water bath before drawing it
up into a tuberculin syringe may facilitate the ease of
In using Phenol Careful patient positioning
to allow phenol to settle into the desired location is important, and contrary
to the concepts associated with patient positioning
for alcohol neurolysis.
Dilute and concentrated intrathecal phenol
Dilute intrathecal phenol can producea transient local anesthetic blockade, while increased concentrations can produce significant neural damage.
Phenol concentrations have a direct relationship with
the extent of neural damage
At concentrations less than
5%, phenol instigates protein denaturation of axons and
surrounding blood vessels. At concentrations greater than
5%, phenol can produce protein coagulation and nonselective.
When compared to alcohol, phenol seems to facilitate
axonal regeneration in a shorter period of time.
Systemic doses of phenol in excess of 8.5 g are associated with toxic side effects.
These effects initially are convulsions, followed by CNS depression, and, finally, cardiovascular collapse.
Chronic long-term exposure may be associated with
renal toxicity, skin lesions, and gastrointestinal effects.
However, phenol is not classically used in long-term
settings, and the customary doses of less than 100 mg are unlikely to produce any systemic effects
The pain location should be determined with
dermatome and sclerotome mapping, and preferably
isolated with a diagnostic injection of local anesthetic or contrast dye under fluoroscopy.
When using phenol, the patient’s
targeted anatomy must be
facing down, the patient leaned 45 degrees supine, and the spinal needle diameter must be larger due to the increased viscosity. The
“sinking” of phenol into its area of effect requires the targeted rootlets to be under the site of administration
The feeling of warmth from the phenol is fleeting, and may provide some pain relief, but neurolysis is slower to manifest than with alcohol
The phenol can take 15 min before it starts to exert its effect. Although there is less outward diffusion with phenol compared to alcohol, the patient should be maintained in position for 30 min after phenol administration. The full effect of phenol manifests over approximately 24 hrs
A short, 20-gauge needle should allow the thick
phenol solution to be injected in most situations. However,
if this proves difficult
warming the injectate in a warm water bath before drawing may ease the flow of the injection.
Drug and Dose
Like alcohol, phenol is injected in 0.1-ml increments, with 60 to 90 s between subsequent injections. Phenol is injected up to a total dose of 0.5 to 0.7 ml.
An epidural neurolytic block provides
bilateral pain relief;
Epidural neurolysis is used for
abdominal cancer pain of both visceral and mixed somatic
and visceral origin
Epidural neurolysis remains popular, not only due to its
increased safety index and the ease for
repeated injections, but also for its greater efficacy on thoracic
and cervico-thoracic junction pain.
EPIDURAL NEUROLYTIC BLOCK
Selecting the appropriate
size needle depends on the agent used
The use of
phenol in glycerin requires a large-bore needle, while the
use of aqueous phenol, phenol in saline, or alcohol permits
the use of a much smaller needle, in which case an epidural needle or catheter may be used.
EPIDURAL NEUROLYTIC BLOCK
a soft, nonkinking, styletted version that can be maneuvered with precision, and allows confirmation of position with the injection of a small amount of local anesthetic.
EPIDURAL NEUROLYTIC BLOCK
Unlike the intrathecal administration of neurolytic
agents, needle or catheter tip location should be chosen
near the vertebral levels that correspond to the dermatomal levels manifesting in the patient’s pain area in order to
deposit the medication over the appropriate nerve roots.
EPIDURAL NEUROLYTIC BLOCK
Once needle and patient positioning have been established, what is performed to confirm proper
needle depth and location.
the use of contrast-enhanced fluoroscopic imaging and a local
anesthetic test dose
EPIDURAL NEUROLYTIC BLOCK
Doses ranging from 2 to 5 ml are usually adequate,
with doses increasing as location moves more caudally
WITH INTRATHECAL AND EPIDURAL
incomplete block to
limb weakness or bladder/rectal paresis
the most common complication is failure of the procedure to provide significant pain relief.
Poor pain relief can have numerous etiologies.
patients to have high expectations for pain relief and have those expectations not met by neurolysis. Another
cause of inadequate pain relief may be as simple as an
incomplete block that can be remedied with a repeat dose. there is always the possibility that the block works well, but that local spread of the neurolytic agent may have produced peripheral damage
There are complications due to entry into the anatomic space where these medications are administered. They include
postdural puncture headaches, meningitis, arachnoiditis, and
neural damage due to trauma. Postdural headaches usually resolve quickly, within 1 to 5 days.
Complications related to neurolytic agents include
loss of motor function
due to neurolysis of the ventral rootlets, loss of touch and
proprioception, and loss of sphincter tone. Of these potential complications, loss of bowel or bladder sphincter
tone is relatively common. The complications caused by
the neurolytic agents are usually transient.
Complications can be
specific to location along the spine where the neurolysis is
At the cervical level, damage can occur to the brachial plexus, most often manifesting as limb paresthesias.
Complications at the thoracic level are the least common
relative to the cervical and lumbar level. Below the L1 spinal level, injections may travel into the cauda equina,
where anterior and posterior roots are not separated. This
factor that may make the degree of motor or sensory effect difficult to predict.
blocks are frequently associated with
neuritis and deafferentation
pain, in addition to postinjection dysesthesias
Neurolytic intercostal blocks may help with pain that
the thoracic wall, abdominal wall, or parietal perineum.