Chemical
Neurolysis
Neurolytic blocks are indicated for patients
with severe, intractable cancer pain in whommore conventional therapy proves
inadequate or conventional analgesic modalities are accompanied by unacceptable
side effects. The most common chemical neurolytic techniques utilized for
cancer patients are celiac plexus, lumbar sympathetic chain, hypogastric
plexus, and ganglion impar blocks. Chemical neurolysis may also occasionally be
used in patients with refractory benign neuralgia and, rarely, in patients with
peripheral vascular disease. These blocks can be associated with considerable
morbidity (loss of motor and sensory function), so patients must be selected
carefully, and only after thorough consideration of alternative analgesic
modalities. Moreover, although the initial result may be excellent, the
original pain may recur, or new (deafferentation or central) pain will develop,
in a majority of patients within weeks to months.
Temporary destruction of nerve fibers or
ganglia can be accomplished by injection of alcohol or phe-nol. These
neurolytic agents are not selective, affect-ing visceral, sensory, and motor
fibers equally. Ethyl alcohol (50–100%) causes extraction of membrane phospholipids
and precipitation of lipoproteins in axons and Schwann cells, whereas phenol
(6–12%) appears to coagulate proteins. Alcohol causes severe
pain on injection, thus local anesthetic is usually administered first. For
peripheral nerve blocks, alcohol may be given undiluted, but for sympathetic
blocks in which large volumes are injected, it is given in a 1:1 mixture with
bupivacaine. Phenol is usually painless when injected either as an aqueous
solution (6–8%) or in glycerol; a 12% phenol solution can be prepared in
radiopaque contrast solution.
Neurolytic celiac plexus or splanchnic nerve
blocks may be effective for painful intraabdominal neo-plasms, especially
pancreatic cancer. Lumbar sym-pathetic, hypogastric plexus, or ganglion impar
neurolytic blocks can be used for pain secondary to pelvic neoplasms.
Neurolytic saddle block can provide pain relief for patients with refractory
pain from pelvic malignancy; however, bowel and blad-der dysfunction should be
expected. Neurolytic intercostal blocks can be helpful for patients with
painful rib metastases. Additional neurodestructive procedures, such as
pituitary adenolysis and cor-dotomy, may be useful in end-of-life palliative
care.
When considering any neurolytic technique, at
least one diagnostic block with a local anesthetic solution alone should be
used initially to confirm the pain pathway(s) involved and to assess the
potential efficacy of the planned neurolysis. Local anesthetic solution should
again be injected immediately prior to the neurolytic agent under fluoroscopic
guidance. Following injection of any neurolytic agent, the nee-dle must be
cleared with air or saline prior to with-drawal to prevent damage to
superficial structures.
Many clinicians prefer alcohol for celiac plexus
block and phenol for lumbar sympathetic block. For subarachnoid neurolytic
techniques, very small amounts of neurolytic agent (0.1 mL) are injected.
Alcohol is hypobaric, whereas phenol in glycerin is hyperbaric; the patient
undergoing subarachnoidneurolysis is carefully positioned so that the solu-tion
travels to the appropriate level and is confined to the dorsal horn region
following subarachnoid administration.
Cancer patients frequently receive
anticoagula-tion therapy if they are at elevated risk for venous thromboembolic
phenomena. When such a patient has discontinued anticoagulant medication in
prep-aration for a diagnostic local anesthetic block, it may be more practical
to obtain consent for a neurolytic procedure in advance and to follow the diagnostic
block immediately with chemical neurolysis if the diagnostic procedure has
resulted in pain relief.
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