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I. Intracranial physiology

The development of the central nervous system (CNS) is incomplete at birth; maturation continues until the end of the first year of life. Cerebral blood flow (CBF) affects cerebral blood volume (CBV), intracranial volume, and, in turn, intracranial pressure (ICP). In children from 3 to 12 years of age, the CBF is 100 mL/100 g/minute and is higher than in adults. The CBF in children from 6 to 40 months is 90 mL/100 g/minute and in newborns and premature infants, it is approximately 40 to 42 mL/100 g/minute.
Autoregulation in the newborn is easily impaired or abolished. This can lead to intraventricular hemorrhage (IVH) with grave consequences. Recent studies have demonstrated that hyperventilation restores autoregulation in the neonate and that CBF velocity changes logarithmically and directly with end-tidal carbon dioxide tension (ETco₂) in infants and children. Under normal conditions, ICP depends more on CBF and CBV than on cerebrospinal fluid (CSF) production. All inhalational anesthetics must therefore be used with care because they increase CBF and CBV by producing vasodilatation.

II. Anesthetic requirements

The anesthetic requirements in pediatric patients vary with age and maturity. Neonates and premature infants have decreased anesthetic requirements relative to older children. The reasons for the lower requirements in babies are the immaturity of the newborn's nervous system, the presence of maternal progesterone, and elevated levels of endorphins, along with the immaturity of the blood-brain barrier. Neonates do sense pain and can develop a stress response to surgical stimulation. They therefore require adequate levels of anesthesia to blunt the stress response. Because the neonate's immature organ systems are sensitive to anesthetic drugs, a narcotic-based anesthetic offers more hemodynamic stability, but emergence may be delayed because the liver and kidneys are not fully developed. Induction of anesthesia in infants is more rapid, however, because of the following:
The ratio of alveolar ventilation to functional residual capacity (FRC) is 5:1 in the infant and 1.5:1 in the adult.
The neonate has a greater cardiac output per kilogram of body weight than the adult.
More of the neonate's cardiac output goes to the vessel-rich group of organs including the brain (up to 25%) and the heart.
The infant has a lower blood-gas partition coefficient for volatile anesthetics and a lower anesthetic requirement.
1. The rapid induction of anesthesia occurring with most volatile anesthetics may be hazardous in the premature, small for gestational age, or unstable patient.
2. Whatever the choice of anesthetic drugs, sick neonates require resuscitation and normalization of fluid and electrolyte balance before the induction of anesthesia.
The common denominator of neonatal surgery is that the operations are frequently performed emergently. This contributes significantly to the >10-fold increase in perioperative morbidity and mortality in neonates compared to other pediatric age groups. Additional difficulties can arise because intraoperative hypoxia and hemodynamic instability can be the first indication of previously unrecognized congenital cardiac and pulmonary anomalies. Regression to fetal circulation may also occur intraoperatively in neonates because of hypercarbia, hypoxia, hypothermia, and acidosis. In addition, respiratory complications are not uncommon in neonates owing to the small size of their airway, laryngotracheal lesions, craniofacial anomalies, and acute (e.g., respiratory distress syndrome, transient tachypnea of the newborn) or chronic (e.g., bronchopulmonary dysplasia) lung disorders.

III. Anatomy of the airway

The newborn period is defined as the first 24 hours of life. The neonatal period is the first 30 days of extrauterine life and includes the newborn period. The infant is an obligate nose breather in part because of the immaturity in the coordination between respiratory efforts and the oropharyngeal motor and sensory input. Conditions such as congenital choanal atresia or simple nasal congestion can cause respiratory distress and asphyxia in the infant.
The oxygen demand in the infant is high: 7 to 9 mL/kg as compared to 3 mL/kg in the mature state. Infants have a high closing volume, high minute ventilation-to-FRC ratio, and soft pliable ribs. Therefore, even some degree of airway obstruction can have a major impact on the oxygen supply in the neonate.

IV. Anesthetic considerations

Preoperative assessment. The preoperative assessment of a pediatric patient who has neurologic dysfunction involves establishing the degree of change in the cerebral compliance. The clinical presentation varies with the age of the patient as well as the rapidity and degree of change in the intracranial contents. Infants might present with a history of irritability, lethargy, and failure to feed. They may have an enlarging head circumference, bulging fontanelle, or lower extremity motor deficits. Older children might have headache, nausea, vomiting, or change in the level of alertness. Funduscopic examination might reveal papilledema. This can be a late sign in neonates owing to the presence of an open fontanelle. Some children, especially neonates, might need further evaluation by pediatric cardiologists and other subspecialists because of the presence of cardiopulmonary disorders and other coexisting diseases.
Fluid balance. The evaluation also includes assessing any fluid and electrolyte imbalance from lack of intake or active vomiting because of changes in the ICP. Furthermore, fluid restriction and the combination of hyperosmolar (e.g., mannitol) and diuretic (e.g., furosemide) therapy may result in hemodynamic instability and shock when coupled with intraoperative blood loss. It is therefore necessary to establish and maintain normovolemia throughout the perioperative period. Normal saline (or other nonglucose-containing solution) may be used as the maintenance fluid because it is slightly hyperosmolar to plasma. Enough glucose is administered to prevent hypoglycemia (vide infra). It is imperative to secure excellent intravenous access for fluid and blood replacement and drug delivery before the start of the operation because the opportunities to do so will be limited once the operation is in progress. Two large-bore intravenous catheters are necessary for children undergoing craniotomy, craniofacial reconstruction, or extensive spine procedures.
Administration of glucose. The administration of glucose-containing fluids during neurosurgical procedures is determined by the intraoperative measurement of blood glucose. The automatic addition of glucose to intraoperative maintenance fluid is unnecessary because hypoglycemia may not be a common occurrence in fasting pediatric patients, even in infants <1 year of age. This is especially true because the stress response to surgery itself results in hyperglycemia from increased sympathoadrenal activity with decreased glucose tolerance, decreased glucose utilization, and increased gluconeogenesis. Furthermore, the hyperglycemia caused by excessive glucose administration can be detrimental in pediatric patients at risk for hypoxic-ischemic insults.
Solutions containing 1% to 2.5% glucose are less likely to cause hyperglycemia than are 5% solutions, especially when administered at a rate of 120 mg/kg/hour (2 to 5 mg/kg/minute), which is sufficient to maintain an acceptable blood glucose level and prevent lipid mobilization in infants and children. The monitoring of intraoperative blood glucose and the continual adjustment of glucose administration may be necessary during long procedures, after prolonged preoperative fasting, and for neonates and small infants, infants of diabetic mothers, infants who have intrauterine growth retardation, children who are small for their age, children receiving extensive transfusion (because the preservative solution in blood products contains glucose), and children who have Beckwith-Wiedemann syndrome, hypopituitarism, adrenal insufficiency, pancreatic islet cell adenoma or carcinoma, large hepatoma, fibroma, or sarcoma, and pheochromocytoma.
The rate of delivery of hyperalimentation may need to be reduced owing to a decrease in the glucose requirement of children receiving hyperalimentation. Alternatively, they may receive a continuous infusion of dextrose 10% in water (D10W), but still require intraoperative glucose monitoring. Other patients who may require the intraoperative monitoring and administration of glucose include neonates under the age of 48 hours, children fasted during the daytime, patients who have poor nutritional status, and patients under regional anesthesia (especially subarachnoid block) which attenuates the stress response to surgery and lowers blood glucose concomitantly.
Premedication. Sedative premedication should be avoided in all patients suspected of increases in ICP because these drugs might further embarrass respiration, cause hypercarbia and cerebral vasodilatation, and lead to tonsillar herniation. Patients scheduled for the repair of vascular lesions whose ICP is normal may be sedated to control preoperative anxiety and avoid hypertension and rupture of the vascular abnormality.
Inhalational anesthetics. Inhalational anesthetics affect mean arterial pressure (MAP), ICP, and cerebral perfusion pressure (CPP) in children. At 0.5 and 1 minimum alveolar concentration, sevoflurane, isoflurane, and desflurane in 60% nitrous oxide (N₂O) increase ICP and decrease MAP and CPP in a dose-dependent manner. There is no relationship between the patient's baseline ICP and the ICP elevation after exposure to sevoflurane and isoflurane. Desflurane, however, may increase ICP to a greater extent in children whose ICP is elevated preoperatively. Because the effect of a change in MAP on CPP is 3 to 4 times greater than the effect of a change in ICP, maintaining MAP is the more important factor in preserving CPP. For children who have a known increase in ICP, intravenous anesthesia may be the better alternative.
Monitoring. Monitoring depends on the patient's age and condition and the planned surgical procedure. Routine monitoring includes the use of the precordial stethoscope, electrocardiogram (ECG), oxygen saturation (Sao₂) by pulse oximeter, ETco₂, noninvasive blood pressure (NIBP) measurement, esophageal stethoscope and temperature probe, and a peripheral nerve stimulator to monitor the degree of neuromuscular blockade. Direct arterial blood pressure monitoring, at least two good peripheral intravenous catheters, and a urinary catheter are recommended for extensive and invasive surgical procedures. Measurement of central venous pressure (CVP) may not reflect intravascular volume accurately, especially in patients in the prone position, so that the risk of inserting a CVP catheter may exceed the benefits.
Venous air embolism (VAE). VAE occurs commonly during craniotomy in infants because of the head position and surgical approach. The head of a small child is large in relation to the rest of the body, causing it to lie above the heart, even in the supine position. In addition, the head of the bed is often elevated to facilitate drainage of blood and CSF during operation. Pressure within the superior sagittal sinus decreases as the head is elevated, increasing the likelihood of VAE. Patients who have a patent ductus arteriosus or foramen ovale are also at risk for paradoxical air embolism through these defects. Consequently, precordial Doppler ultrasonography is used in conjunction with ETco₂ sampling and direct measurement of arterial blood pressure for detecting and assessing treatment of VAE. The optimal position for the Doppler probe is on the anterior chest just to the right of the sternum in the fourth intercostal space. The probe may also be positioned on the posterior chest in infants weighing <6 kg. The anesthesiologist may also elect to monitor for the presence of nitrogen in the end-tidal gas mixture. Because the risk of VAE is present- and VAE has occurred- in the sitting, prone, and supine positions, the use of N₂O should be avoided to prevent an increase in the size of entrained air bubbles.
Neurophysiologic monitoring. Electrocorticography and electroencephalography (EEG) necessitate low concentrations of inhalational anesthetics. Inhalational anesthetics and N₂O depress somatosensory evoked potentials for operations on the spine and brain stem; a narcotic technique may be preferable. The use of electromyography and motor evoked potentials requires that muscle relaxation be reversed during electromyography and monitoring of muscle movement.
ICP monitoring. ICP monitoring has seen increased utilization in the management of pediatric head injury because it facilitates the achievement of preset physiologic and biochemical goals and the assessment of patients' response to therapy. ICP after traumatic brain injury is controlled by maintaining normal colloid osmotic pressure and decreasing hydrostatic capillary pressure. Microcirculation around contusions is enhanced by maintaining normovolemia and decreasing sympathetic discharge by maintaining adequate levels of anesthesia. This approach has been correlated with an improvement in outcome from traumatic brain injury over the past 10 years.
Temperature regulation. Because hypothermia is an issue in infants and small children, they require active heating in the operating room by elevating room temperature, using warm-air blankets, radiant warming lights, and humidification of inspired gases, and warming intravenous fluids.
Positioning. The extended duration of neurosurgical procedures and the unusual access requirements necessitate paying close attention to the positioning of the patient before placing surgical drapes through the use of padding potential pressure points, checking peripheral pulses, and avoiding stretching of peripheral nerves. For patients operated in the prone position, there must be free movement of the abdominal wall without undue flexion of the head. Excessive neck flexion may cause the endotracheal tube to kink, exert excessive pressure on the tongue, or advance the tube into a mainstem bronchus. The resultant hypoxia and hypercarbia will increase ICP, causing upper spinal cord and lower brain stem ischemia. Patients who already have posterior fossa abnormalities such as a mass lesion or Arnold-Chiari malformation are especially at risk for this complication. Patients may also experience flexion-induced swelling of the head and tongue from obstruction of venous and lymphatic drainage and resultant postextubation obstruction of the airway or croup. Extreme rotation of the head can also limit venous return through the jugular veins, increasing ICP, impairing cerebral perfusion, and causing bleeding from cerebral veins.
Emergence. The goals for emergence include prompt awakening to aid early assessment of neurologic function, hemodynamic stability, and minimal coughing or straining on the endotracheal tube to avoid intracranial hypertension and bleeding. Patients may receive fentanyl before emergence; arterial hypertension is treated with vasoactive drugs such as esmolol and labetalol. Naloxone is avoided because its use has been associated with uncontrolled hypertension and coughing when the endotracheal tube is in place.
The trachea is extubated after the patient responds to commands or when infants and toddlers open their eyes. Alternatively, some anesthesiologists prefer to extubate the trachea when the patient is still deeply anesthetized if there is no contraindication (e.g., intraoperative catastrophe, loss of airway reflexes, poor preoperative condition). If the patient's awakening is delayed and no anesthetic cause can be determined, the presence of a neurologic issue can be revealed by a computed tomographic (CT) scan before tracheal extubation.
Postoperative intubation. In several circumstances, the patient's trachea remains intubated into the postoperative period. Operations that interfere with cranial nerve nuclei or brain stem function with resultant impairment of airway reflexes and respiratory drive require ongoing airway protection and ventilation until these functions can be assessed. The loss of several blood volumes, even with replacement, may necessitate continued maintenance of an artificial airway and protection of the airway reflexes. Also, prolonged operation in the prone position may lead to edema of the face and airway with the possibility of airway obstruction after extubation.
Postoperative care. Complications in the postoperative period involve a number of organ systems. Respiratory dysfunction occurs frequently after posterior fossa craniectomy. There may also be airway obstruction secondary to either edema or cranial nerve injury and apnea from injury to the respiratory control center in the brain stem. Operative injury to either the hypothalamus or the pituitary gland can lead to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) or diabetes insipidus (DI) with seizures, changes in the level of consciousness, and abnormalities of fluid and electrolyte (especially sodium) balance. When children require sedation for endotracheal intubation postoperatively, the administration of propofol is not recommended for long-term sedation because there have been reports of children who have developed metabolic acidosis, lactic academia, and bradyarrhythmias after prolonged administration. The guideline is to limit the infusion of propofol to a period of not longer than 5 days.

V. Neuroanesthetic management

Hydrocephalus
Definition. Hydrocephalus is the enlargement of the ventricles from increased production of CSF, decreased absorption by the arachnoid villi, or obstruction of the CSF pathways. Hydrocephalus is classified as communicating (nonobstructive) or noncommunicating (obstructive). The causes of the increased CSF collection can be congenital or acquired.
a. Etiology
(1) Congenital. Aqueductal stenosis, myelomeningocele, Arnold-Chiari malformation, spina bifida, Dandy-Walker syndrome, mucopolysaccharidoses (with obliteration of the subarachnoid space), achondroplasia (with occipital bone overgrowth).
(2) Acquired. IVH, space-occupying lesions, infections (abscess and meningitis).
Hydrocephalus causes an increase in the head circumference. Prevention of any further increase in intracranial contents is vital as this increase may precipitate herniation. Drainage of CSF can also be a problem because ventricular arrhythmias may be associated with the rapid removal of CSF. In some circumstances, epidural or subdural hemorrhage can result from a sudden reduction in the ICP. This sudden change in ICP from the hemorrhage can cause a change in the level of consciousness of the child, although the shunt may still be functioning.
Surgical procedures include ventriculoperitoneal shunt, ventriculoatrial shunt, ventriculopleural shunt, ventriculojugular shunt, and ventriculostomy.
Preoperative management. Assess the patient for any effects of increased ICP such as nausea, vomiting, changes in the ventilatory pattern, irritability, decreased level of consciousness, bradycardia, or hypertension. A CT scan might demonstrate increase in the size of the ventricles. Sudden neurologic deterioration in the pediatric patient must be treated quickly with emergency endotracheal intubation, muscle relaxation, hyperventilation with ETco2 monitoring, and administration of cerebral vasoconstricting drugs (e.g., barbiturates) and diuretics (e.g., mannitol, furosemide) until emergency surgical reduction of the ICP is achieved. Control of the ICP is sometimes accomplished by a direct needle puncture of the lateral ventricle and aspiration of CSF.
Premedication. Sedation is contraindicated because the resulting hypoventilation may increase ICP. EMLA cream (eutectic mixture of local anesthetics: lidocaine and prilocaine) may be used whenever possible to achieve intravenous access without causing distress to young patients.
Anesthesia. An inhalation induction is usually not attempted because all inhalational anesthetics are cerebral vasodilators and can increase ICP. A modified rapid-sequence intravenous induction is preferred to minimize the risk of aspiration from either gastric hypotonia secondary to the effects of increased ICP or a recent meal. Preoxygenation is followed by intravenous induction with a sedative-hypnotic (e.g., barbiturate, propofol) and a fast-acting nondepolarizing muscle relaxant such as rocuronium for intubation. Muscle relaxation is maintained throughout the procedure along with total intravenous anesthesia (TIVA) with propofol and fentanyl. Intravenous fluid is given at a maintenance level, and either intravenous ceftriaxone or vancomycin is given (after checking sensitivity) slowly (over 60 minutes) and in a diluted solution to prevent histamine release. At the end of the procedure, the stomach is suctioned and the trachea is extubated when the patient is fully awake. This is usually not a problem as long as the shunt is functioning well.
Craniosynostosis. Craniosynostosis is a congenital anomaly resulting from premature fusion of the cranial sutures. It can cause severe cranial deformity, depending on the involved sutures, and, rarely, intracranial hypertension and psychomotor retardation from abnormal brain growth. Males are more often affected than females. Sagittal synostosis accounts for nearly half of all cases of craniosynostosis. Surgery is usually performed in the first 6 months of life for best results.
Preoperative assessment. Patients are otherwise healthy but require assessment for any evidence of increased ICP. Hemoglobin is determined preoperatively, and blood is made available for surgery. The surgeons work in close proximity to major venous sinuses, so sudden and massive blood loss is a possibility. Blood loss also increases as the number of involved sutures increases.
Monitoring. Monitoring includes ECG, Sao₂, ETco₂, NIBP, and esophageal temperature as well as an arterial catheter for direct blood pressure and arterial blood gas (ABG) measurement and a precordial Doppler to monitor for VAE. The patient must have at least two good lines for adequate intravenous access and a urinary catheter to monitor urinary output.
Anesthesia. Induction of anesthesia is either inhalational or intravenous if a catheter is already in place. The endotracheal tube is well secured so that ventilation is undisturbed with head movements. Anesthesia is maintained with an inhalational agent, air/oxygen, an intermediate-acting nondepolarizing relaxant, and a narcotic (fentanyl or morphine) for analgesia.
A key point in the procedure occurs when the surgeons manipulate the sagittal sutures due to the possibility of VAE or massive bleeding. The possibility of VAE may be decreased by maintaining intravascular blood volume and entrainment of air attenuated by continuous monitoring with Doppler ultrasonography. If evidence of VAE exists, alerting the surgical team enables members to irrigate the entire field with saline, which, along with assumption of the head-down position, prevents further entrainment of intravenous air and enhances hemodynamic stability. If a central venous catheter is in place, the anesthesiologist attempts to aspirate air from the central circulation.
Postoperative management. At the conclusion of the procedure, the patient is first awakened and then the trachea is extubated. The hematocrit is measured during the recovery period because blood loss continues from the surgical incision, and patients may need either blood or blood products to counteract oozing. Maintaining adequate urine output throughout the procedure indicates the adequacy of regional organ perfusion.
Tumors. Intracranial tumors are the most common solid tumors of childhood and the second most common pediatric cancer after the leukemias. Supratentorial tumors account for approximately half of all intracranial malignancies and arise from midline structures. Two-thirds of the infratentorial tumors are in the posterior fossa. The pathologic distribution includes gliomas (30%), medulloblastomas (30%), astrocytomas (30%), ependymomas (7%), and others (3%: acoustic schwannomas, meningiomas, etc.). All intracranial tumors increase intracranial volume. Infratentorial lesions produce signs and symptoms of brain stem compression and intracranial hypertension from hydrocephalus secondary to obstruction of flow of CSF. Craniopharyngioma, the most common tumor of the hypothalamic-pituitary area, may cause disorders of the neuroendocrine system including DI.
Preoperative considerations. Signs and symptoms of increased ICP are noted, and the need for performing either a ventriculostomy or a shunt before the definitive operation is determined. Patients most commonly present with headache and vomiting for several days and sometimes weeks. Neonates and infants may have a history of poor feeding, irritability, or lethargy. The anterior fontanelle may bulge, eyes may exhibit a "sunset sign,"� or the cranium may be enlarged. There may be obvious engorgement of the scalp veins, and some patients may show changes in the level of consciousness or focal neurologic deficits, depending on the area of brain compression. Posterior fossa tumors may cause cranial nerve dysfunction along with signs and symptoms of increased ICP. An endocrine evaluation may also be indicated if a craniopharyngioma is suspected along with a plan for steroid replacement to compensate for damage to the hypothalamic-pituitary axis. The hypovolemia and electrolyte imbalance caused by DI are corrected before surgery is undertaken.
Anesthetic considerations
1. The history is reviewed, including the presence of seizures and measures to control them, and documented. A complete physical examination to identify any neurologic deficits is also performed and noted.
2. The anesthesiologist assesses the patient for signs and symptoms of increased ICP and DI and reviews the results of investigative procedures such as CT scan and magnetic resonance imaging (MRI).
3. Measures to control ICP including insertion of either a ventriculostomy or shunt before the definitive operation are noted. Elevated ICP can also be decreased by the use of dexamethasone (to reduce peritumoral edema), furosemide (which also reduces CSF production), or hypertonic saline. The routine use of mannitol is not advised when the presence of a craniopharyngioma is suspected because it may interfere with the intraoperative identification of DI.
4. Patients who have increased ICP may have either altered gastric emptying or dehydration and electrolyte imbalance from poor feeding, vomiting, and SIADH.
5. The patient's position is discussed with the surgeon, and the head is positioned to avoid any obstruction to venous return. The Mayfield horseshoe headrest is used for prone positioning because pins may cause skull fractures, dural tears, and intracranial hematomas. Blood is typed and cross-matched and immediately available in the operating room. Intraoperative DI, although more common in the postoperative period, is treated with intravenous aqueous vasopressin and administration of intravenous fluid.
6. Monitoring for the operation to remove an intracranial tumor includes the use of all routine monitors and a urinary catheter. In addition, an arterial catheter for direct hemodynamic monitoring and determination of blood chemistry is necessary for pediatric patients undergoing craniotomy. A central venous catheter is recommended when blood loss is expected, when there is a concern about DI and SIADH, or when the head position and the surgical approach increase the risk of VAE. The femoral vein is recommended for central venous access in small children because of the ease of entry and lack of interference with cerebral venous drainage as may occur when the jugular veins are cannulated.
Anesthesia. Induction is focused on measures to reduce the ICP. The recommended sequence is intravenous induction, hyperventilation, and gentle, brief laryngoscopy to secure the airway. The use of bupivacaine 0.25% with epinephrine 1:200,000 to infiltrate the scalp before the skin incision confers analgesia and decreases the anesthetic requirement and the bleeding. Limiting the total dose to 1 mL/kg of the bupivacaine 0.25% mixture avoids toxicity.
Intraoperative concerns include optimal positioning of the head, maintaining body temperature, and adequately replacing fluid and blood loss. The anesthetic technique (air; oxygen; low concentration of inhaled anesthetic; a nonhistamine-releasing, nondepolarizing muscle relaxant; and a short-acting narcotic) is designed to avoid oversedation and allow early assessment of neurologic function at the completion of surgery. Positioning and hyperventilation may be used to minimize brain swelling. If necessary, mannitol, 0.25 to 1 g given intravenously, and furosemide may be added, although this negates the use of urine output as an indication of intravascular volume status.
A smooth and prompt emergence from anesthesia is desirable. The decision to extubate the trachea of pediatric patients depends not only on the length of the procedure but also on the intraoperative course of events, the extent of the tumor resection, the expected neurologic deficits, the probability of loss of protective airway reflexes and attendant need for airway protection, the possibility of seizures, and the degree of need for postoperative control of ICP. Operation in the posterior fossa may cause either damage to or edema around the brain stem respiratory center or cranial nerves innervating the vocal cords and soft tissues of the upper airway with resultant apnea, stridor, or postextubation airway obstruction. The administration of drugs including phenytoin and the monitoring of ABG, hematocrit, blood chemistry, fluid balance, and neurologic function are continued in the postoperative period.
Surgery for epilepsy. Patients who require operation for epilepsy have intractable seizures owing to congenital disorders, birth trauma, tumors, or vascular malformations. Continual seizure activity has deleterious effects on the development of the brain and causes psychosocial dysfunction.
Perioperative risks arising from status epilepticus include severe hypoxemia and sudden death. The chronic use of large doses of anticonvulsant (e.g., phenytoin and carbamazepine) for the medical management of seizures may alter pharmacologic response because of enzyme induction, liver dysfunction, and jaundice. This may result in rapid metabolism and clearance of anesthetic drugs including narcotics and muscle relaxants. Anesthetic requirements are therefore increased, and patients require more frequent administration of anesthetic drugs.
Preoperative assessment. Assessment involves determining the age of onset, type, and frequency of the seizures and any deleterious effects on mental status and development. Recent changes in the level of consciousness and the appearance of new motor deficits must be recognized preoperatively and documented. Liver function tests and a coagulation profile are performed preoperatively.
When targeting important areas of the brain such as the motor cortex and the speech centers, surgery is performed under local anesthesia if the patient is a cooperative older child or adolescent. Young children and those with evidence of anxiety, developmental delay, and psychiatric illness need general anesthesia. For awake procedures, establishing rapport with the patient and explaining the state of dissociation, lack of pain (neuroleptanalgesia), and need for cooperation are essential for the success of the operation. No sedatives or anticonvulsants are administered for 48 hours if electrophysiologic studies are to be conducted intraoperatively. All patients receive dexamethasone for 48 hours to control brain swelling. Ultrashort-acting barbiturates are readily available to control seizure episodes in the perioperative period. A comfortable position and constant visual contact between the patient and anesthesiologist are essential.
Blood loss may occur from a large craniotomy, especially in the smaller patient, so blood must be available. The fluid warmer is used to maintain normothermia. The patient well padded because these procedures may be lengthy.
Monitoring. Routine monitors, including a urinary catheter, are employed, and normocapnia is maintained during the procedure. Intravenous catheters, arterial catheters, and nerve stimulators are placed on the limbs not being used by the surgeons to observe motor function during the localization of the seizure focus. This is discussed with the surgeons in advance and explained to the patient. Neurophysiologic monitoring is used to guide the actual resection of the epileptogenic focus because it may be in close proximity to areas in the cortex controlling memory, speech, and sensory and motor function. General anesthesia can affect the sensitivities of these modalities.
Anesthesia. All inhalational anesthetics depress cerebral activity and are avoided during EEG studies. The successful use of low concentrations of isoflurane in combination with narcotics has been reported in several centers. N₂O is avoided for repeat craniotomies, as for removal of electrocorticographic leads or depth electrodes, until the dura is opened because intracranial air may persist for up to 3 weeks after the initial craniotomy. Propofol induces dose-dependent changes in the EEG with an increase in beta activity at low infusion rates and an increase in delta activity, followed by burst suppression, at high infusion rates. Etomidate is not recommended because it produces interictal spiking and might induce clinical seizures in these patients. Ketamine activates epileptogenic foci in epileptic patients and is not recommended. A combination of droperidol and fentanyl or propofol and fentanyl can be used during awake craniotomies. The propofol is discontinued 20 minutes before electrophysiologic monitoring is to begin.
Nondepolarizing relaxants have no effect on electrical activity. The dose requirements are higher due to the interaction with the anticonvulsant drugs. No muscle relaxant is used during the period of direct cortical stimulation so that the surgeons can observe motor activity. This is essential when cortical stimulation of the motor strip is performed under general anesthesia.
Postoperative management. Careful monitoring of neurologic function is vital during the first 24 hours after the operation. Motor, memory, or speech dysfunction or increased seizure activity may occur in the postoperative period. The hematocrit is monitored because blood loss from a large cranial incision can be considerable. Postoperative pain must be controlled to avoid episodes of hypertension. Short-acting barbiturates or propofol must be available to treat seizure activity.
Head trauma. Skull fractures occur at all ages as a result of birth injury, traffic and playground accidents, domestic negligence, or abuse. They may be depressed, open, or basal skull fractures and increase morbidity and mortality if unrecognized.
Traumatic sequelae include epidural, subdural, and intracerebral hematomas, cerebral contusion, and edema with signs of intracranial hypertension.
1. Epidural hematomas. Epidural hematomas account for 25% of all intracranial hematomas and are considered to be true medical emergencies. Most frequently caused by a tear in the middle meningeal artery, epidural hematomas can lead to a decreasing level of consciousness, pupillary dilatation, hemiparesis, posturing, or coma. Patients require urgent surgical evacuation of the hematoma and achievement of intracranial hemostasis.
2. Subdural hematomas. Subdural hematomas result from parenchymal contusion or blood vessel tears sustained during birth trauma or shaking, as in shaken baby syndrome. They can cause brain edema and progressive neurologic dysfunction.
3. Skull fractures. Skull fractures are of concern if they involve major blood vessels. Depressed fractures require surgical elevation and might be associated with dural lacerations. Signs and symptoms depend on the extent of cortical injury. Basilar fracture might cause periorbital ecchymoses, hemotympanum, changes in the level of consciousness, and seizures.
Preoperative considerations. A CT scan helps in the assessment of the extent of neurologic injury and possible intracranial hypertension. Establishing an airway, maintaining adequate ventilation and circulation, and determining the level of consciousness, associated injuries causing cardiovascular instability, and thermoregulatory problems are of paramount concern. The cervical spine is evaluated and immobilized until the presence of a cervical fracture is ruled out. Renal function must be investigated and the urine checked for hematuria. Blood for transfusion must be available and circulating blood volume restored with blood or crystalloid or both. The need for preoperative evaluation of hematocrit, coagulation profile, and acid-base and electrolyte balance depends on the type and extent of injury. Blunt trauma to the abdomen and long-bone fractures can be major sources of blood loss.
Monitoring. Routine monitors, urinary catheter, and arterial catheter for direct blood pressure monitoring are essential. Adequate intravenous access is necessary for volume resuscitation.
Anesthesia. The trachea is intubated with the head in "neutral position" to avoid any injury to the cervical spine, and ventilation is controlled to avoid increasing ICP. Volume resuscitation precedes the rapid-sequence induction of anesthesia, which is achieved by the administration of thiopental or propofol, a narcotic, and a nondepolarizing muscle relaxant of rapid onset. The dose of sedative-hypnotic is reduced in hypovolemic patients. Maintenance of anesthesia with air, oxygen, low-dose inhalational anesthetic, and narcotic allows prompt emergence for early neurologic assessment. Poor preoperative condition and adverse intraoperative events mitigate against early awakening and extubation.
Postoperative care. Control of ICP is vital in the postoperative period. The patient may remain asleep and mechanically ventilated in the intensive care unit if there is concern about either neurologic or organ system dysfunction.
Meningomyelocele and encephalocele. Embryologic neural tube fusion takes place during the first month of gestation. Failure of fusion causes herniation of the meninges (meningocele) or elements of the neural tube (myelomeningocele) and can occur at any level of the spinal cord. Abnormality occurring at the level of the head is referred to as encephalocele. Defects arising at higher levels in the spine can produce bowel, bladder, and lower extremity dysfunction. Most patients also have Arnold-Chiari malformation and hydrocephalus. Surgery is performed at the earliest opportunity (usually in the first week of life) to avoid infection of the CNS. It is important to note that these patients frequently have or may develop latex allergy, either because of repeat exposure (as from frequent catheterization) or because of a genetic propensity, and need to be treated from birth as if the patients do have a latex allergy. The anaphylactic reaction that may result from exposure to latex ranges from airway involvement (tingling of the lips, facial swelling, wheezing) to cardiovascular collapse. Severe anaphylaxis is treated with the administration of fluid, epinephrine, vasopressors, steroids, and diphenhydramine (Benadryl).
Preoperative preparation. Patients are evaluated for signs and symptoms of hydrocephalus and the presence of any airway problems due to a large encephalocele or thoracic myelomeningocele. There may be considerable evaporative losses with consequent problems in maintaining body temperature and fluid balance. Hematocrit must be checked preoperatively and blood made available for transfusion because blood loss may occur during the repair of large defects. The defect should be well padded in the perioperative period to avoid further complications from compression, CSF leak, bleeding, and infection.
Monitoring. Routine monitoring is used. Patients who are expected to incur blood loss should have adequate intravenous access for transfusion, an arterial line, and a urinary catheter. Electromyographic monitoring is used to identify functional nerve roots during operation for tethered cord release. The goal is to minimize injury to nerves innervating muscles of the anal sphincter and lower extremities.
Anesthesia. Intravenous access should be established before induction. Positioning and airway management may be particularly challenging with a large encephalocele. The patient is placed in the lateral or supine position with the encephalocele or myelomeningocele padded in a "doughnut"� support. Intravenous atropine is given and the trachea intubated either awake or after the intravenous administration of a sedative-hypnotic (e.g., thiopental, propofol) and a nondepolarizing muscle relaxant. The eyes are taped closed, the patient turned to the prone position, and the limbs padded. Additional relaxant should not be given if the surgeons plan to use intraoperative nerve stimulation and electromyographic monitoring, and anesthesia is maintained with a low concentration of inhalation agent and a narcotic suited to the length of the procedure. Temperature, blood loss, and fluid balance are monitored closely during the procedure. The trachea is extubated after the patient awakens at the end of the procedure and neurologic integrity has been confirmed. Infants who are at risk of postoperative apnea should have oxygen saturation and apnea monitors in place for overnight observation.
Craniofacial surgery. Cranial deformities are syndromes associated with premature closure of the cranial sutures. Premature closure may be one manifestation of a number of congenital syndromes and is often associated with anomalies involving the heart or other organs. Patients may be born prematurely and have respiratory dysfunction in addition to a difficult airway from the craniofacial deformity.
Preoperative preparation
1. Detailed evaluation of the etiology of the craniofacial abnormality as well as the presence of associated anomalies is vital. Careful note of any anticipated airway management problems must be made. Previous anesthesia records must be reviewed if the patient has had cardiac or other corrective surgeries in the past.
2. The choice of laboratory investigations depends on the specific craniofacial defect and may include an echocardiogram or consultation with a cardiologist.
3. Consideration of tracheotomy for airway management in the perioperative period is an important aspect of patient evaluation.
4. Massive blood loss is always a concern during these procedures. Therefore, adequate amounts of blood and blood products should be available.
5. The ambient temperature in the operating room is increased to facilitate the maintenance of body temperature and airway humidity during what frequently turns out to be a lengthy procedure.
6. Fluid warmers are used to warm infusions. Blood replacement is started early and continued in the postoperative period.
Monitoring involves the use of routine monitors, Doppler if the patient's head is positioned above the heart during surgery; direct arterial blood pressure measurement, which also facilitates the measurement of ABGs, hematocrit, and electrolytes; and a urinary catheter.
Anesthesia
1. Establishment of good intravenous access is important because these procedures tend to be long and involve massive blood loss.
2. Every attempt is made to keep the patient warm during surgery by increasing the ambient temperature and using a forced-air warming blanket, heated humidifier, and fluid warmer.
3. The successful maintenance of fluid balance is ascertained by hematocrit and urine output.
4. The coagulation profile is checked after replacement of one blood volume, especially if continued loss and replacement are expected.
5. Air embolism is a concern when there is extensive bone dissection.
6. Resuscitation drugs should be available during the procedure.
Anesthesia can be induced with either an inhalational anesthetic (e.g., sevoflurane) if airway problems are anticipated or with intravenous drugs if the patient has an intravenous catheter in place and there is no potential problem with the airway. The endotracheal tube must be well secured, especially if the patient will be operated in the prone position. Eyes are lubricated with hypoallergenic ointment and taped securely closed. All pressure points must be well padded. Surgeons can request the intraoperative reduction of intracranial volume to help with the retraction of the frontal lobes during dissection of the orbital structures. Maintenance of anesthesia is usually with air, oxygen, a long-acting nondepolarizing muscle relaxant, and a narcotic for analgesia.
Postoperative care. Intubation of the trachea continues into the postoperative period mainly to ensure adequate ventilation. Airway and breathing problems may arise owing to the length of the procedure, expected fluid shifts from massive transfusion, and the use of intraoperative narcotics. Postoperative transfusion might be required because of continued oozing from the surgical site.
Vascular anomalies. Large arteriovenous malformations (AVMs) are associated with high-output congestive heart failure in infants who may require hemodynamic support.
The initial treatment is by the interventional neuroradiologist who performs selective intravascular embolization. Because the operation for the ligation of an AVM is associated with considerable blood loss, hemodynamic monitoring and good intravenous access are essential. The anesthesiologist also needs to be prepared to treat the sudden hypertension and hyperemic cerebral edema that may develop after ligation of the AVM. This treatment includes hyperventilation and the administration of labetalol and sodium nitroprusside.
Moyamoya disease is a chronic vasculo-occlusive disorder of the carotid arteries so named because, on angiography, the vessels appear as a "puff of smoke." The syndrome is associated with neurofibromatosis, Down's syndrome, previous intracranial radiation, and hematologic disorders. Patients present with either transient ischemic attacks or recurrent strokes. Anesthetic management involves the enhancement of cerebral perfusion through adequate preoperative hydration, intraoperative maintenance of the preoperative blood pressure, and maintenance of normocapnia to avoid steal from ischemic areas of the brain. The combination of air, oxygen, and narcotic confers a stable level of anesthesia and permits the use of intraoperative EEG monitoring. Cerebral perfusion is maintained in the postoperative period through optimal intravenous hydration and adequate pain management to avoid cerebral vasoconstriction from hypertension and hyperventilation.

VI. Neuroradiology

Anesthetic management of neurodiagnostic and neurointerventional procedures. Most pediatric patients require general anesthesia for neuroradiologic diagnostic procedures such as CT scanning, MRI, angiography, and myelography, as well as interventional procedures and radiation therapy because of age (infants), anxiety, lack of understanding and cooperation, developmental delay, and inability to remain still for lengthy procedures. Sedation is employed in older, cooperative children undergoing short procedures that do not produce pain and discomfort. Anesthesia is frequently administered in locations remote from the operating suite, which means that the same equipment and level of assistance must be available. In addition, the radiologists and their staff must be oriented so that they understand the anesthesiologist's issues and concerns regarding pediatric patients.
MRI makes use of the intense magnetic field emanating from the large static magnet. Ferromagnetic objects should never be brought into the room housing the magnet. The patient must also be absolutely still and isolated within the tunneled scanning space (which may induce claustrophobia) during the examination. The procedure does not cause any pain to the patient and usually takes approximately 45 minutes to 1 hour. All ferromagnetic objects must be removed from the patient because they may induce motion artifact in the magnetic field. Patients must also be checked for metal objects such as aneurysm clips and cochlear implants. The intravenous infusion of propofol administered by means of an MRI-compatible pump is an effective anesthetic technique for these procedures. Alternatively, inhalation anesthesia may be administered with an MRI-compatible anesthesia machine using a laryngeal mask (LMA) or an endotracheal tube.
CT scanning also requires understanding and cooperation on the part of the patient who will need to remain still throughout the procedure to secure diagnostic images of high quality. Sedation is used to enhance patient cooperation. Neonates may be scanned without any sedation because they will fall asleep, but infants might need general anesthesia with intravenous or inhalational drugs for the procedure. Sedation is also required in older children who are either uncooperative or mentally handicapped. Healthy children who are older may be scanned without sedation as long as they are assured it will be painless. Patients undergoing stereotactic-guided radiosurgery require general anesthesia.
Angiography is used mainly as an adjunct to diagnostic CT scanning and MRI. Its main indication is for the detailed demonstration of AVM's and moyamoya disease, as well as the extent of tumor vascularity. Cerebral angiography is usually performed through the transfemoral route with an injection of nonionic contrast agents and requires general anesthesia in small children.
Periprocedural management includes the following activities:
1. Review the patient's history and any previous diagnostic or surgical procedures and their management.
2. Check that the consent form has been signed and the patient has been fasting.
3. Discuss the procedure with the parent and the older patient and develop rapport with the younger patient.
4. Ensure adequate functioning of the anesthesia machine and suction apparatus and the availability of equipment for difficulty in airway management and resuscitation.
5. Apply all standard monitors routinely used in the operating room: ECG, blood pressure, pulse oximeter, ETco2, and temperature.
6. Institute controlled ventilation with normocapnia for patients undergoing cerebral angiography to achieve good-quality images after the injection of the intravenous contrast.
7. Because allergic or anaphylactic reactions are always a possibility with the contrast material used during CT scan, MRI, and angiographic procedures, document history of any allergic reactions and be prepared to treat a reaction if one occurs during the procedure.
8. Monitor patients in a recovery area until they are fully awake and stable before discharging them from the unit. Patients who exhibit an anaphylactic reaction might require intubation, ventilation, and overnight observation because laryngeal edema is a possible sequela of allergic reactions.
9. Monitor patients during transportation from remote locations if they require recovery in the postanesthesia care unit. In addition, procedures that begin in the radiology suite may be continued in the operating room, necessitating that the patients remain anesthetized and monitored during transportation.