Epileptic Seizures
Epileptic seizures result from paroxysmal neuronal discharges
of abnormally excitable neurons. Six percent to 10% of individuals younger than
70 years will experience a seizure at some time during their lifetime. Fifty percent
to 70% of patients with one seizure will never have another. However, 70% of people
with two seizures will have an epileptic focus, be candidates for antiseizure medications,
and be subject to withdrawal seizures after anesthesia if such medications are not
continued.[627]
A seizure is the term for the clinical
event defined as a paroxysmal alteration in neurologic function caused by a synchronous,
rhythmic depolarization of brain cortical neurons. Epilepsy is the condition manifested
by recurrent, unprovoked seizures. Sometimes syncopal episodes can be mistaken for
seizures, especially when interviews are compressed in the short time frame of a
preoperative visit. We believe that each patient who gives a history of recent undiagnosed
syncope or seizure should be seen by a specialist in this field before proceeding
with anesthesia because anesthesia can provoke these conditions (see later).[628]
Twenty-five percent of patients with a seizure have a normal electroencephalogram
(EEG) when interictal. Thus, a negative EEG does not indicate that someone with
a seizure will not have a withdrawal seizure when emerging from anesthesia. Seizures
can be generalized (arising from deep midline structures in the brainstem or thalamus,
usually without an aura or focal features during the seizure), partial focal motor,
or sensory seizures (the initial discharge comes from a focal unilateral area of
the brain, often preceded by an aura). As with cerebrovascular accidents and coma,
knowing the origin may be crucial to understanding the pathophysiologic processes
of the disease and to managing the intraoperative and postoperative course.
Epileptic seizures can arise from discontinuation of sedative-hypnotic
drugs or alcohol, use of narcotics, uremia, traumatic injury, neoplasms, infection,
congenital malformation, birth injury, drug use (e.g., amphetamines, cocaine), hypercalcemia
or hypocalcemia, blood in the ventricle or hypoxia, and vascular disease and vascular
accidents. Thirty percent of epileptic seizures have no known cause. Most partial
seizures are caused by structural brain abnormalities (secondary to tumor, trauma,
stroke, infection, and other causes).
An epileptic patient requires no special anesthetic management
other than that for the underlying disease. Most authorities believe that anticonvulsant
medications should be given in the therapeutic range[627]
[628]
[629]
and
continued
through the morning of surgery, even in pregnant women; they should also be given
postoperatively, even in mothers who plan to breast-feed, according to guidelines
published by the American Academy of Neurology.
Many of the epileptic drugs, including phenytoin, carbamazepine, and phenobarbiturate,
alter the hepatic metabolism of many drugs and induce cytochrome P450 enzyme activity.
Drug-drug interactions are much less problematic with the newer epileptic drugs
such as gabapentin and topirimate.[627]
Appropriate
treatment of status epilepticus may include general anesthesia.[629]
In one controlled trial, phenobarbital was more rapidly effective in controlling
status epilepticus than was diazepam followed by phenytoin.[629]
The frequency of side effects and required tracheal intubation was similar for both
regimens. High concentrations of enflurane (especially with hyperventilation) can
be associated with EEG evidence of epileptic activity and tonic-clonic movements.
[630]
These seizures, however, do not appear to
have serious sequelae. Enflurane anesthesia does not seem to increase seizure activity
in patients with a history of convulsive disorders, and it even suppresses seizures
induced by electroshock, pentylenetetrazole, strychnine, picrotoxin, or bemegride.
[631]
Thus, other than the use of current drug
therapy
and heeding precautions taken for the underlying disease, no known changes in perioperative
management seem to be indicated.
