Sunday, April 1, 2012

Anesthesia For Epilepsy Surgery (PART 1)


Seizure must differentiated from epilepsy ,in that the one is an event and the other is process.

Chronic recurrent epilepsy affects about 0,5% to 1% of population with about 25% to 30% of epileptic having seizure more than once per month.

It is estimated that 2% to 5% of the population will experi-
ence a nonfibrile seizure at some point during their lifetime.

Idiopathic seizures usually begin in chilldhood,whereas the onset of epilepsy in an adult should arouse suspicion of focal brain disease such as intracranial tumor,head trauma or infection.

Withdrawal from alcohol or other addicting drug may also be a cause of seizure in an adult.The EEG is the most important test,although a normal tracing does not exclude the possibility of epilepsy.

Although it has been estimated that almost 4% of non epileptic patient will have an abnormal EEG the sensitivity
of the EEG for the detection of abnormalities in the epilep-
tic population is over 90%.

MRI is superior to computed tomography in detecting a fo- 
cal intracranial lesion such as atrophy.Examination of CSF is indicated if infection is a possible cause of seizures.


Approximately 300.000 people have medically uncontrolled epilepsy in USA.

About 13% of these are thought to be candidate for brain                  surgery but only about 1% actually undergo procedure.

The first surgical resection for epilepsy was performed in 1886 by Harsley.

The important and crucial issue for these patients is to be operated on time that is before the terrible impact of their 
disease on psychosocial development of a child.   

Young children with evidence of focal cortical disorders and intractable epilepsy should be considered for surgery as soon as possible,since continous seizure have detererious effect on the brain development.

An adolescent with complex partial seizures of mesial tem- poral origin and evidence of mesial sclerosis on MRI should be considered for surgery.

Traditionally the anesthesiologist's role in the management of the epilepsy patient has been to provide an anesthetic that does not trigger seizures.

At present this task may entail providing appropriate seda-
tion or monitored anesthetic care for awake craniotomy
administering anesthetic drugs to provoke seizures for intraoperative ECoG or providing a technique that has anti convulsant properties.

Neuroanesthesiologist intensivist are helping to determine the cerebral depressant most appropriate for stopping sei-
zures,proconvulsant and anti convulsant properties of anes-
thetics and the important interactions between anesthetic  therapy and epilepsy or antiepileptic drugs.

Finally neurologist and neurosurgeon consult with anesthe-
siologist to determine the optimal management of refracto- ry status epilepticus.

Brain surgery is a reasonable alternative treatment when medications fails to control seizures.

The type of surgery(brain and non brain) usually employed
are devided into four categories.

The first category:entails resection of spesific focus,mostly typically represented by anterior temporal lobectomy.

The second category entails interruption of seizure circuits
to prevent generalization as with a corpus callosotomy.

Multiple subpial transection may also be used,perticularly 
when the focus includes vital,non resectable brain tissue.
The third category is vagal nerve stimulation.

Finally a recent report describes a fourth category entailing
electrical stimulation of the centromedian thalamic nucle-
us,but this approach is not yet in wide spread use.

Preoperative evaluation:(1,3)

Preanesthetic assessment is facilitated by the long and me-
ticulous approach of the other participant.

All patients are interviewed during preoperative evaluation
and informed the details of the anesthetic procedure.

The planned anesthetic regiment,the use of arterial and urinary catheter are explained at length.All questions and 
concerns are discussed thoroughly to ensure patient coope-
ration and concent.

In addition to the general medical evaluation of the system
attention should be paid to some features particular to the
epileptic patient.

Psychosocial factors :

Psychological and socioeconomic factors deeply affect the
epileptic patient who lives with a constant sense of dread
that another attack may supervene.

The importance of psychological  approach is particularly
evident in children.

Although many children with epilepsy learn and behave nor-
mally,a disproportionate number are learning -disabled and
suffer minor behavioral disturbances.

Children with epilepsy,especially if they are brain injured
are prone to a variety of behavioral disturbances that in-
clude impulsivity,temper tantrums and attention deficit disorders with or without hyperactivity.

By the second decade,some form of psychological dysfunc-
tion my be found in more than one third of patients with 
epilepsy,with 11 percents of the group manifesting signs
of overt psychotic thinking.

EEG evaluation :                                                                                

Extensive EEG studies evaluate the seizure focus,
attempting  to localize it to a small discrete area usually in the temporal lobe.

If scalp recording is unable to identify an unilateral focus 24 hours monitoring is instituted.Surgical implantation of subdural and possibly subcortical eleectrodes is sometimes necessary.

A Wada test which done to evaluate hemisphere dominance 
involves the intracarotid infusion of sodium amobarbital 
while the patient is talking and holding both arms in the air

As the rapidly acting barbiturate exerts its effect,the contralateral arm falls.

If the patient's speech simultanously stop,the injected hemisphere is probably dominant.

The test is repeated on both sides because of the possibili-
ty of mixed dominance of speech.In cases where the identi-
fied epileptogenic focus is located on the speech dominant
hemisphere ,awake craniotomy during temporal lobectomy
is carefully considered.

As long as it was considered essential to have the patient 
awake for the successful outcome of the neurosurgical pro-
cedure,the mandate of the neuroanesthesiologist was de-
fined in the following terms.
          * No medication with a potential to alter the EEG 
            recording should be used.
          * Anesthetic agents should not interfere with the
            electrical stimulation process of the cortex.
          * The patient should be alert and cooperative and
             should participate in verbal and motor testing if
          * The patient should be given sedation and analge-
             sia to tolerate the long craniotomy procedure.
          *  The anesthesiologist should control adequately
              sudden burst of epileptic activity and if necessa-
              ry,administer a general anesthetic to permit ter-
              mination of the procedure.
to be continued


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