NEUROLOGIC COMPLICATIONS
Nerve injury is a recognized complication of peripheral regional
techniques. In a series involving more than 100,000 regional anesthetics, the frequency
of neurologic complications after peripheral blockade was less than that associated
with neuraxial techniques and was associated with pain on needle placement or injection
of local anesthetic.[84]
Risk factors contributing
to neurologic deficit after regional anesthesia include neural ischemia, traumatic
injury to the nerves during needle or catheter placement, infection, and choice of
local anesthetic solution. However, postoperative neurologic injury due to pressure
from improper patient positioning, tightly applied casts or surgical dressings, and
surgical trauma is often attributed to the regional anesthetic. Patient factors
such as body habitus or a preexisting neurologic dysfunction may also contribute.
Although needle gauge, type (i.e., short versus long bevel), and
bevel configuration may influence the degree of nerve injury after peripheral nerve
block, the findings are conflicting, and there are no confirmatory human studies.
Theoretically, localization of neural structures with a nerve stimulator would allow
a high success rate without increasing the risk of neurologic complications, but
this has not been established. Serious neurologic injury has been reported after
uneventful brachial plexus block using a nerve stimulator technique.[16]
Likewise, prolonged exposure, high-dose, or high concentrations of local anesthetic
solutions may also result in permanent
neurologic deficits. In laboratory models, the addition of epinephrine increases
the neurotoxicity of local anesthetic solutions and decreases nerve blood flow.
However, the clinical relevance of these findings in humans remains unclear. Nerve
damage caused by traumatic needle placement, local anesthetic neurotoxicity, and
neural ischemia during the performance of a regional anesthetic may worsen neurologic
outcome in the presence of an additional patient factor or surgical injury.[7]
Prevention of neurologic complications begins during the preoperative
visit with a careful evaluation of the patient's medical history and appropriate
preoperative discussion of the risks and benefits of the available anesthetic techniques.
It is imperative that all preoperative neurologic deficits are documented to allow
early diagnosis of new or worsening neurologic dysfunction postoperatively. Postoperative
sensory or motor deficits must also be distinguished from residual (prolonged) local
anesthetic effect. Imaging techniques, such as CT and MRI, are useful in identifying
infectious processes and expanding hematomas. Although most neurologic complications
resolve completely within several days or weeks, significant neural injuries necessitate
neurologic consultation to document the degree of involvement and coordinate further
workup. Neurophysiologic testing, such as nerve conduction studies, evoked potentials,
and electromyography, are often useful in establishing a diagnosis and prognosis.
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