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2015-03-05 01:09 毕业

Epilepsy Anesthesia: current status and perspectives
Yi Tang, Jian-Xiong An
Department of Anesthesiology & Pain Medicine, Tsinghua University Yuquan
Hospital
Epilepsy is one of the most common neurologic diseases in the world. Many
clinicians used to treat the disease via medication, yet serious side-effects of long
medicinal administration and intractable seizures sometimes, if not often, say "No" to
the therapy despite the development of a variety of specific anticonvulsant drugs.
Today's advances in neuroimaging such as PET and fMRI and
electroencephalography may offer them with detailed anatomical targets that mediate
some medically intractable seizure disorders, which may then be cured by
neurosurgical procedure. We will highlight the perioperative management of some
patient undergoing epileptogenic foci resection.
Physiology of the patients
Surgical procedures may not be the first choice of some patients suffering from
epilepsy. Basically, they turn to neurosurgical procedures only after they are in
despair to internal medicine. However, Hepatic function may be seriously affected by
long administration of those antiepileptic drugs. Attentions should be also paid to the
renal functions due to probable deficit renal system. In addition, age should be
considered especially in infants and younger children because of their lower abilities
to compensate the changes during perioperative managements. Furthermore,
neurocognitive deficits should be evaluated then.
Preoperative evaluation and preparation
A general preoperative organ system-based evaluation of the patient is essential
to minimize perioperative morbidity. Uncompleted preoperative evaluation and
preparation are at high risk for perioperative morbidity and mortality. Respiratory and
cardiac related events account for a majority of these complications. A complete
airway examination is essential because some craniofacial anomalies may require （科教论文网 lw.nseaC.Com编辑发布）
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specialized techniques to secure the airway[1]. Potential heart disease may not be
obvious immediately after been accepted in hospital and a cardiologist should
evaluate patients with suspected problems to help optimize cardiac function prior to
surgery if necessary. In addition, communicating with those patients is extremely
important to secure their mental health. While laboratory tests should be tailored to
the proposed neurosurgical procedure. Given the risk of significant blood loss
associated with craniotomies, a hematocrit, prothrombin time, and partial
thromboplastin time should be obtained to uncover any insidious hematological or
coagulation disorders. Type and cross-matched blood should be available prior to
those patients. Because each drug class may affect the conduct of anesthesia, whoever
present for epilepsy surgery have undergone pharmacological treatments of their
seizures. Potent inducers of hepatic microsomal P-450 enzymes include some classic
anticonvulsant drugs, such as phenobarbitol, phenytoin, and carbamazepine. The
hepatic P-450 enzymes mediate biotransformation and so enhanced elimination of
many drugs. Long-term administration of these specific anticonvulsant drugs may
result in drug resistance and increase dosages for both nondepolarizing muscle
relaxants and opioids administered during general anesthesia[2]. Sodium valproate
may cause platelet abnormalities, bleeding disorders, and induce liver failure[3], and a
patient receiving these drugs should have the appropriate laboratory tests to determine
the baseline line platelet and liver function prior to surgery.
Induction of anesthesia
Appropriate technique and drugs may be used according to the patient's
neurological status and coexisting disorders for induction of anesthesia. General
anesthesia induction can be conducted via venous procedure, while infants and young
children may be induced using inhalation of sevoflurane and nitrous oxide in

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oxygen.[4] Though sevoflurane has been shown to have epileptogenic potential, the
mechanism of this phenomenon remains unclear. A muscle relaxant (nondepolarizing
or depolarizing) may then be administered to facilitate intubation of the trachea.
These drugs rapidly induce unconsciousness and can blunt the hemodynamic effects
of tracheal intubation. Patients with nausea or gastroesophageal reflux disorder are at
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risk for aspiration pneumonitis and should have a rapid-sequence induction of
anesthesia performed with thiopental or propofol, immediately followed by a
rapid-acting muscle relaxant and cricoid pressure[5,6]. A thorough examination of the
airway and the use of appropriate equipment and techniques are mandatory during
inducing pediatric patients because of the relatively short trachea, which may cause an
endotracheal tube easily migrating into a mainstem bronchus if an infant's head is
flexed or turned. Patients undergoing awake craniotomies are always at risk for
airway compromise due to sedation, seizure, or obstruction due to positioning.
Therefore, the patient's face should be accessible to the anesthesiologist for
manipulation of the airway and ventilation of the lungs[7].
Positioning
Patient positioning for surgery requires careful preoperative planning to allow
adequate access to the patient for both the neurosurgeon and anesthesiologist. This is
especially important in patients undergoing awake craniotomies. A clear channel
should be made in front of the patient's face to facilitate communication and facial
observation during the neuropsychological assessment. If cortical situation or
induction of the seizure is planned, the patient's limbs should be easily visualized.
Compression and stretch injuries can occur and necessitate padding under the arms
and legs. Many neurosurgical procedures are performed with the head slightly
elevated to facilitate venous and CSF drainage from the surgical site[6]. However,
superior sagittal sinus pressures decrease with increasing head elevation, and this
increases the likelihood of venous air emboli (VAE).Extreme rotation of the head can
impede venous return through the jugular veins and lead to impaired cerebral
perfusion and increased ICP and venous bleeding. Vascular access Typically, two
large bore venous cannulae are sufficient for most craniotomies. Central venous
cannulation may be necessary if initial attempts fail. Utilization of the femoral vein
avoids the risk of pneumothorax associated with subclavian catheters, and does not
interfere with cerebral venous return, as may be the case with jugular catheters.
Furthermore, femoral catheters are more easily accessible to the anesthesiogist during
operations on the head. Cannulation of the radial artery would provide direct blood
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pressure monitoring and sampling for blood gas analysis.
Maintenance of anesthesia
Several classes of drugs used to maintain general anesthesia. Volatile anesthetic
agents (i.e., sevoflurane, isoflurane, halothane, and desflurane) are administered by
inhalation. Sevoflurane has virtually replaced halothane and isoflurane as the
principal anesthetic for induction of anesthesia in infants and children. But th agents
depress the EEG and may interfere with intraoperative electrocorticography
(ECoG)[8]. So volatile anesthetics are rarely used as the sole anesthetic for
neurosurgical procedure. Intravenous anesthetics are categorized as sedative/hypnotic
and opioid. The sedative/hypnotics, propofo

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