Anesthesia for Neurosurgical Procedures in Children

Hemangi S Karnik; Chinmaya P Bhave

Anesthesia for Neurosurgical Procedures in Children

^{1, ^*}Hemangi S Karnik MD

¹Department of Anesthesiology, Lokmanya Tilak Municipal Medical College and General Hospital Mumbai, Maharashtra, India

²Chinmaya P Bhave MBBS DNB PDF

²Department of Anesthesiology, Kokilaben Dhirubhai Ambani Hospital Mumbai, Maharashtra, India

ABSTRACT

Pediatric neuroanesthesia is a unique subspecialty as it deals with a patient age group whose central nervous system is in a constant state of development. The pediatric neuroanesthesiologist is expected to have thorough knowledge of normal pediatric physiology and pharmacology as well as neurophysiology and neuropharmacology. In addition, good understanding of neuroanesthesia principles is needed. This Article deals with neurophysiology and perioperative management of pediatric neurosurgical patients in general and specific aspects of some commonly done neurosurgical procedures.

INTRODUCTION

In a pediatric patient, the central nervous system has several anatomical and physiological differences as compared to adults. A basic understanding of these age-dependent variables of neurophysiology, anesthetic drug-related neuropharmacology and anesthetic implications of the specific surgical procedure are essential to reduce patient morbidity and to help in good outcome.

DEVELOPMENTAL NEUROANATOMY

Embryologically, the central nervous system is one of the earliest systems to develop in the third week of gestation and last to be completed almost at the end2 of human maturation.

___________________

^*Corresponding author

Email: dr_hemangi@hotmail.com

At birth, the brain weighs about 335 g, providing 10–15% of body weight and reaches adult weight (1,200–1,400 g) by 12 years of age.¹ The fastest growth of brain occurs in the first year of life. To accommodate this growth, the cranial vault is compliant with open cranial sutures and fontanelles in infants. This allows for compensatory increase in the intracranial volume without increase in intracranial pressure (ICP).

While the cranial bones fuse at approximately 12–18 months of age, the posterior fontanelle closes by 2 months and anterior fontanelle closes by 9–18 months.¹ Premature fusion of cranial sutures affects brain growth and development.

Intracranial Pressure

The cranial cavity is a closed structure containing the brain, blood and cerebrospinal fluid (CSF). Any increase in volume of any one of the components necessitates compensatory reduction in other components. Beyond certain limit, in case of large intracranial masses when these compensations fail, ICP will increase. Normal ICP in children may be 3–7 mmHg and in neonates 1.5–6 mmHg² as compared to 8–15 mmHg in adults. A sustained ICP of >7 mmHg is considered as intracranial hypertension in neonates.³

CEREBRAL PHYSIOLOGY

Cerebral Blood Flow

In infants and children, head size is relatively larger as compared to adults and therefore brain receives a larger percentage of blood flow in them. The cerebral blood flow (CBF) in children of 3–12 years is approximately 100 mL/100 g/min, and children of 6 months to 3 years is 90 mL/100 g/min^4,5 whereas in neonates and infants it is lower (40 mL/100 g/min).⁶

In children, CBF is regulated by several factors. Within a set range of blood pressure (BP), cerebral autoregulation allows constant CBF. In adults these values are approximately 60–160 mmHg.⁷ Autoregulatory curve of BP in neonates is shifted to the left as compared to their adult counterparts, with autoregulatory range being 20–60 mmHg in term neonates.⁸ The slope of the autoregulatory curve decreases and increases steeply at lower and upper limit of autoregulation (Figure 1).⁹ The narrow range with sudden change in blood flow puts them at the greater risk of cerebral ischemia in response to low BP and intraventricular hemorrhage in case of higher BP. Cerebral pCO₂ has a direct vasodilatory effect on cerebral vessels and CBF is directly proportionate between pCO₂ of 25–55 mmHg range. There is growing evidence suggesting ill effects of hyperventilation in neonates.¹⁰ Cerebral blood flow increases significantly at pO₂ less than 50 mmHg. Increase in ICP reduces cerebral perfusion.3

Figure 1: Cerebral blood flow in children. Note the narrow range of autoregulation in neonates with steep decrease and increase at both ends and pressure-dependent increase in cerebral blood flow in premature newborn.

Cerebral Metabolism

In younger children, cerebral metabolic rate for oxygen (CMRO₂) is estimated to be 5.2 mL/100 g/min,⁴ and in infants it is 5.8 mL/100 g/min,¹¹ as compared to adult values of 3.2 mL/100 g/min. Neonates have reduced metabolic demand and therefore a lower CMRO₂, approximately 2.8 mL/100 g/min. Similarly, metabolism for glucose is also lowest at birth, but is higher in children as compared to adults.⁷ Hypothermia reduces CMR by 6–7% per °C reduction in body temperature.¹²

Effects of Anesthetic Agents

Various drugs affect CBF by changing vessel diameter, ICP and cerebral metabolism. All anesthetic agents reduce cerebral metabolic demand for oxygen as they produce unconsciousness.

Intravenous Agents

Commonly thiopentone and propofol reduce CMRO₂ by 50%.¹² Etomidate also produces similar effect to a lesser extent. These agents also reduce CBF and ICP. Ketamine increases CMR, CBF and ICP. Opioids and benzodiazepines produce modest reduction in CMR.

Inhalational Anesthetic Agents

Inhalational anesthetic agents are vasodilators and thus increase CBF and therefore ICP. Halothane causes most increase in CBF. They also produce dose-dependent reduction in CMR. Nitrous oxide increases CBF without reducing CMR and therefore has tendency to increase ICP.

PREOPERATIVE EVALUATION

A child presenting for neurosurgical procedure could be healthy with mild symptoms, may be critically ill or be developmentally delayed with other coexisting pathology.

The symptoms like irritability, excessive sleepiness, unconsciousness, nausea, vomiting, seizures and motor weakness may suggest possibility of increased ICP. A history about neurological development should be obtained. Condition-specific history should be obtained.

General examination with assessment of nutrition, hemodynamic parameters and airway examination to assess intubation difficulties should be done. Complete neurological assessment consisting of level of consciousness, motor and sensory functions, and cranial nerves, signs of raised ICP, pupillary signs and reaction to light should be performed. Common signs of increased ICP are bulging fontanelle and cranial enlargement in infants and in older children, diplopia, vomiting, decreased consciousness, hypertension, bradycardia, pupillary dilatation and papilledema. The protective airway reflexes like gag reflex and cough reflex, and evidence of pulmonary aspiration of gastric contents should be checked. In addition, children with raised ICP may be dehydrated and hence should be assessed for fluid and electrolyte disturbances.

The evaluation of other systems for identifying coexisting abnormalities should be done.

Investigations

A complete hemogram is mandatory for most surgical procedures. Coagulation studies, serum creatinine, arterial blood gases, chest radiograph and electrocardiogram (ECG) should be individualized, while serum electrolyte levels are asked in children with suprasellar lesions. In children on anticonvulsants or antitubercular treatment, liver function tests should be sought for. Children with intracranial abscesses should be evaluated for coexisting cyanotic heart diseases. Blood grouping and cross-matching should be performed for all major neurosurgical procedures.

ANESTHETIC MANAGEMENT

Though each patient and each surgery mandate a specific anesthetic plan, some common principles apply to most cases. Some common neurological conditions and their anesthesia implications are listed in table 1.

Premedication

A patient with increased ICP may be sensitive to effects of sedative premedication and even a small dose may cause airway obstruction and respiratory depression, leading to hypercarbia. Therefore, sedative premedication, like midazolam or opioids if needed, should be given only under supervision. Oral or intranasal midazolam is useful to reduce separation anxiety and produce amnesia in conscious patients with normal ICP.

Monitoring

Intraoperative monitoring includes ECG, pulse oximeter, appropriate sized noninvasive BP, capnograph and temperature monitoring. Precordial or esophageal stethoscope should also be used in smaller patients. An intra-arterial monitoring of BP is recommended for all major craniotomies and craniofacial reconstruction

Table 1 Neurological Conditions and Anesthesia Implications

Neurological condition	Anesthetic implications
Developmental delay	Difficult communication, poor nutrition, neuromuscular disease
Unconsciousness	Airway obstruction, aspiration, respiratory depression, poor nutrition
Craniofacial abnormalities	Upper respiratory tract infection, airway difficulties, blood loss, air embolism
Arteriovenous malformations	Potential congestive heart failure
Meningocele	Latex allergy
Chiari malformation	Apnea, airway difficulties
Neuromuscular dystrophies	Malignant hyperthermia, respiratory failure, sudden cardiac death
Hypothalamic/Pituitary lesions	Aspiration pneumonitis, diabetes insipidus, hypothyroidism, adrenal insufficiency
Denervation injury	Hyperkalemia after succinylcholine, resistance to nonepolarizing muscle relaxants
Chronic anticonvulsant therapy	Hepatic and hematological abnormality, increased metabolism of anesthetic drugs

6 surgeries, where sudden, severe hemodynamic changes are expected. A central venous catheter is useful when venous air embolism (VAE) is anticipated or as an alternative intravenous access.

Urine output should be measured in prolonged procedures, where major blood loss and fluid shifts are anticipated or osmotic agents are to be administered. Neuromuscular junction monitoring is helpful to ensure adequate muscle paralysis in patients on antiepileptics.

Specialized monitoring like intraoperative electrocorticography (ECoG), electroencephalography (EEG) or evoked potential (EP) monitoring may be needed in certain surgeries.

Induction of Anesthesia

The anesthesia technique is decided as per the patient’s age, the preoperative neurological status and other comorbid conditions. Goal of anesthesia induction is to avoid sudden increase in ICP, CMRO₂ and CBF. For children with an intravenous access, anesthesia can be induced with intravenous propofol (2–4 mg/kg) or thiopentone sodium (4–8 mg/kg).^9,10,13 Propofol causes pain on injection but have additional antiemetic effect. Though etomidate 0.2–0.3 mg/kg causes less hemodynamic instability in hypovolemic patients, it can produce nausea, vomiting, reduce seizure threshold and suppress adrenocortical axis.¹⁴ Ketamine is not preferred in neuroanesthesia practice as it can cause neuroexcitation and increases ICP.

General anesthesia (GA) may be induced using sevoflurane in oxygen-air combination till intravenous access is secured. Halothane has essentially been replaced by sevoflurane in neuroanesthesia as halothane increases ICP, can produce hypotension, has longer duration of action leading to delayed recovery and has potential for liver dysfunction. Sevoflurane produces smooth induction and rapid recovery. Inhalational induction is also preferred in anticipated difficult airway cases. A patient with increased ICP can have delayed gastric emptying. Rapid sequence induction (RSI) using thiopentone or propofol, followed by succinylcholine or rocuronium, is commonly employed with cricoid pressure in children at the increased risk of aspiration. Use of succinylcholine in children having raised ICPs is allowed as the benefits offered by it mostly outweigh its inherent risk of transient increase in ICP.

Airway Management

Pre-existing hypercarbia and hypoxia should be corrected by gentle ventilation. Adequate depth of anesthesia and neuromuscular blockade must be ensured prior to laryngoscopy to avoid coughing on tracheal intubation with subsequent 7 increases in ICP. Intravenous fentanyl or preservative free lignocaine may be used to prevent hyperdynamic response. As the surgeries are often prolonged, the tracheal tube with minimum leak should be inserted and fixed in such a way that it does not migrate endobronchially after surgical position is given. Airway pressure should be constantly monitored.

A pharyngeal pack should be inserted if there is an appreciable leak resulting in inadequate ventilation or when oral bleeding or CSF leak is expected. Care should be taken to remove the pack postoperatively.

Maintenance of Anesthesia

Inhalational-based anesthesia remains the most widely used in pediatric practice with availability of agents like isoflurane, sevoflurane and desflurane. Addition of nitrous oxide helps in reducing the requirement of inhalational anesthetics. All inhalational agents have potential to cause dose-dependent myocardial depression. This should be kept in mind while anesthetizing patient in head high or sitting position.

Propofol depresses CMRO₂ and does not cause cerebral vasodilatation like inhalational anesthetics. Hence, it may be used in children; though when used in high doses alone, it can cause hemodynamic instability. Fentanyl is the most commonly used opioid to provide analgesia. In neonates and infants, remifentanil is preferred, as it is not dependent on hepatic metabolism and is metabolized by plasma esterases.

A combination of inhalational and intravenous anesthetics is also suitable in neurosurgery as individual requirements are reduced along with their side effects. Spontaneous ventilation is contraindicated when cranium is open due to increased risk of VAE. Atracurium is used in neonates and infants. Vecuronium, rocuronium or pancuronium can be used in older children, and the degree of neuromuscular blockade should be monitored intraoperatively.

Positioning

To get optimum exposure of the affected areas of brain, the procedures are often done in head turned, lateral, prone or sitting positions. Different positions affect general and cerebral hemodynamics differently and may pose a risk of various stretch injuries. The positioning should be such that it allows for the patient access to the anesthesiologist, minimizes brain retraction, allows easy access to the area to be operated upon and does not greatly interfere with the physiology. Adequate padding of the pressure points should be done to avoid pressure sores. The various positions, their effects on physiology and anesthetic implications are listed in table 2 8.^15–20

Table 2 Commonly Used Positions in Neurosurgery and Their Effects

Position	Physiological effect	Anesthetic implications
Head elevation	Increase in cerebral venous drainage Decrease in CPP Increase in venous pooling in lower limbs	Outward migration of tracheal tube Venous air embolism Postural hypertension
Head rotation/flexion	Compression of jugular vein Kinking of tracheal tube	Increased intraoperative bleeding Tongue edema Increased airway resistance/inability to ventilate Post-extubation airway obstruction and cervical cord compression
Lateral position	Reduced Functional Residual Capacity	Compression of dependent arm veins Brachial plexus injury Nerve compression in dependent arm No access for intravenous or blood pressure in park bench position in dependent arm
Prone position	Reduction in cardiac output Thoracic compression Abdominal compression Pressure on eyes, pressure points	Hypotension Increased airway pressure Increased bleeding in spine surgery Tracheal tube displacement Tongue and oral edema Retinal ischemia Postoperative visual loss Peripheral nerve injuries Pressure sores at pressure points
Sitting position	Reduction in cardiac output Decrease in CPP Kinking of tracheal tube Stretching of cervical cord	Hypotension Venous air embolism Pneumocephalus Increased airway resistance/inability to ventilate Flexion myopathy
CPP, cerebral perfusion pressure

Intravenous Fluid and Blood Administration

The goal of intravenous fluid administration is to maintain normovolemia throughout the procedure. Children presenting for neurosurgery are often volume depleted or dehydrated. This mandates adequate replacement of intravascular volume and electrolytes. Ringer’s lactate and normal saline (RL/NS) are considered a suitable maintenance fluid during neurosurgery despite the theoretical risk of hyperchloremic metabolic acidosis with the latter. Glucose containing fluids are 9 avoided in neurosurgery in general due to the deleterious effect of hyperglycemia on the brain. Monitoring blood sugar levels is needed during the long procedures, in children with prolonged fasting, in diabetic children and in infants and neonates and normoglycemia is maintained.

The estimation of blood loss can be difficult to measure and can be more accurate if the operative field is in view, suctioned bottles are calibrated and hematocrit is estimated intraoperatively. The anesthesiologist should pre-determine the maximum allowable blood loss. Most commonly hematocrit is maintained above 24%. Prompt replacement of blood loss with packed red blood cells and other blood products helps to prevent setting of coagulopathy.

Measures to Reduce ICP

Acute increase in ICP needs to be treated promptly to prevent complications. Several measures are recommended:

Ensure normoxia and normocarbia
Ensure adequate depth of anesthesia and muscle relaxation
Recheck head position for adequate venous drainage from head
Prop-up position, if hemodynamically stable
Use hyperosmolar agent—mannitol 0.5–1 g/kg or 3% NaCl infusion
Small bolus dose of thiopentone or propofol to deepen anesthesia. This can reduce BP, putting the ischemic brain more at risk
Surgical drainage of CSF
Hyperventilation for very short period only. It is important to note that small children are prone to inadvertent hyperventilation and are prone to ischemia.

Venous Air Embolism

Venous air embolism is a potentially serious complication when the head is elevated above the heart level. Due to entrainment of air in the open dural venous sinuses in sitting position, the incidence of VAE is found to be 33% in children below 12 years.¹⁶ To prevent paradoxical air embolism in systemic circulation, preoperative screening of two-dimensional Echo in all children planned for surgery in sitting position is recommended, and it is avoided in the presence of patent ventriculoatrial shunt, presence of intracardiac shunt and in extremes of age.²¹

A sudden decrease in end-tidal CO₂ (ETCO₂), BP or presence of air on Doppler monitor should alert of VAE. Though least sensitive, an esophageal stethoscope may pick up “Mill-Wheel” murmur in the absence of other sensitive monitors. If VAE occurs, FiO₂ should be increased to 100%, surgical field should 10 be flushed with saline, and if possible, air should be aspirated from central venous line, with head positioned below the heart level.

Temperature Management

Core temperature should be monitored using oral, nasopharyngeal or rectal temperature probe for prolonged procedures. To minimize the temperature loss, the operation theater should be warmed to near ambient temperature. In addition, cleaning solutions, irrigating and intravenous fluids should be close to body temperature when used. Use of forced air warming blanket minimizes heat loss and helps to maintain normothermia. Hyperthermia is also frequently seen in pediatric neurosurgical practice in the presence of certain mid-brain or thalamic lesions and in the presence of infection. This should be promptly treated using antipyretics and passive cooling.

Emergence

Preoperative neurological status plays a major role in deciding need for postoperative elective ventilator support. In preoperatively conscious patients, smooth, emergence without major fluctuations in the hemodynamics and ICP is needed. Adequate analgesia and adequate reversal of neuromuscular blockade should be ensured before allowing patient to wake up. Adjuncts like fentanyl or dexmedetomidine may be used prior to extubation to maintain stable hemodynamics and minimize coughing and straining. Extubation should be planned if the child is alert, spontaneously breathing, hemodynamically stable and neurologically well. Any alterations should mandate postoperative ventilatory support in the intensive care unit and sometimes an urgent computed tomography scan to determine cause of decreased neurological function.

Postoperative Management

Postoperative pain can be treated with intravenous opioids with paracetamol as adjunct. Alternatively, nonsteroidal anti-inflammatory agents, intravenously or per rectal suppositories may be used. Care should be taken to avoid drugs causing respiratory depression compromising patient safety or interfering with neurological assessment.

Postoperative complications following neurosurgery include delayed recovery from unconsciousness, airway obstruction, respiratory depression, increased ICP secondary to cerebral edema, hematoma or hydrocephalus, continued blood loss or seizures. All children who have undergone major craniotomy should be shifted to intensive care unit for observation and care.

SPECIFIC CONDITIONS

11With the development of pediatric neurosurgery as subspeciality, a wide variety of surgical procedures are performed with success. Each surgery is unique in its own right in terms of access and demands on the intracranial physiology and therefore their anesthesia management.

Hydrocephalus

Hydrocephalus occurs due to increased intracranial volume of CSF. Majority of hydrocephalus cases are due to obstruction in the CSF pathway leading to decreased absorption. The incidence of congenital hydrocephalus is 0.2–3.5 in 1,000 births.²² In children, the severity of symptoms and clinical signs will depend upon rate of increase in CSF volume and age of the child. A ventriculoperitoneal shunt is the commonest procedure done in hydrocephalus.

While planning anesthesia for these children, care should be taken to minimize the increase in ICP. Due to very large head size, infants are potentially difficult to intubate. A roll under the shoulder or a small mattress under the torso would help in the neck extension and visualization of larynx. Dilated scalp veins can be used if intravenous access at other sites is not available. The tunneling of shunt is most stimulating part of the procedure and additional dose of analgesics should be given along with deepening plane of anesthesia.²³ As surgery involves large body surface area, care should be taken to prevent inadvertent hypothermia.

Complications of shunt procedures include hypotension, dysrhythmias, pneumothorax, accidental bowel injury, shunt infection and malposition. VAE may occur if the shunt system is not kept flushed continuously. Excessive drainage of CSF may occur due to intraoperative CSF loss and repeated shunt chamber compression, leading to risk of subdural hematoma or reverse herniation.

While doing ventriculoatrial shunt, use of endocardial ECG on atrial tip helps in correct placement. Sudden drainage of large amount of CSF into right atrium may lead to congestive heart failure. These children should not receive excessive intravenous fluids.

Congenital hydrocephalus is often associated with Chiari malformation and meningomyelocele. Appropriate positional care for these lesions needs to be provided.

Neuroendoscopy

Neuroendoscopy involves insertion of a neuroendoscope into the cerebral ventricular system through a frontal burr hole. Both diagnostic and therapeutic procedures may be performed under direct vision. Warmed RL or NS is used as 12 irrigating fluids. Endoscopic third ventriculostomy (ETV) to connect the cerebral ventricles with the subarachnoid space below the surface of brain and endoscopic coagulation of choroid plexus are performed for obstructive hydrocephalus in children. The child needs to be kept completely paralyzed during the procedure to prevent any movement or spontaneous respiration. Bradycardia is most frequently seen besides tachycardia, hypotension and hypertension.²⁴ Hypothermia may set in early if cold irrigating fluid is used. Electrolyte disturbances may be seen secondary to either pre-existing abnormality or due to irrigation fluid used.²⁵ As the punctured site in third ventricular floor is very close to basilar artery, injury to it or a branch of the vessel can cause severe bleeding. If surgical bleeding occurs, the control is difficult as vision through endoscope is lost. Therefore, a cross-matched blood should always be kept readily available. As significant air can get entrapped in ventricles, nitrous oxide should be avoided to prevent problems related to pneumoencephalus and pneumoventricle.

Pediatric Head Injuries

About 75% of pediatric trauma patients have head injury. The types of injuries commonly seen include scalp injuries, diffuse cerebral edema, skull fractures, extradural or subdural hematomas and cerebral contusions. Major scalp injuries in small child can lead to significant bleeding and hemodynamic instability. Basilar skull fractures should be suspected in the presence of bleeding from nose or ears, CSF rhinorrhea, bilateral black eyes or ecchymosis behind ears. Nasal intubation or insertion of nasogastric tube should be avoided in such cases. Epidural hematoma patient can suddenly deteriorate after an initial lucid interval.

The child may be irritable, drowsy, confused or unconscious. Vomiting following head injury is common and often precedes sudden neurological deterioration. Besides head injury, other coexisting system trauma should be identified. The aim of anesthesia management is to prevent increase in ICP and to prevent secondary brain injury. Airway should be secured in all children with Glasgow Coma Scale (GCS) less than or equal 8 at the earliest. Care must be taken to not aggravate cervical spine trauma that may be often associated.

To minimize the risk of aggravation of primary insult, additional insults by hypoxia (paO₂ <60 mmHg), systemic hypotension (systolic BP <50^th percentile)²⁶ should be avoided. In hypovolemic patient, as volume of distribution is low, lower doses of intravenous agents are needed for induction of anesthesia. Alternatively an inhalational agent like sevoflurane may be used. Ketamine, though advantageous for shock patient, has potential to increase ICP and hence is not preferred. Etomidate can be used for hypovolemic head injured patient. Nitrous oxide should be avoided in the presence of pneumocephalus. Normocarbia should be maintained.

13Blood glucose levels should be frequently monitored and maintained between 8 and 10 mmol/L.²⁷ Anticonvulsants are provided for about 7 days post injury to reduce incidence of post-traumatic seizures. Spinal cord injuries may also be associated with head injuries and should be ruled out both clinically and radiologically. Injury to spinal cord may be present without radiological evidence in children.

Intracranial Tumors

Intracranial tumors are predominantly seen in midline, unlike adults, and have tendency to produce obstructive hydrocephalus and increased ICP aggravating the neurological condition.

Infratentorial Tumors

Common infratentorial tumors include medulloblastoma, ependymoma, cerebellar astrocytoma, hemangioma and brainstem glioma (Figure 2). The patients usually present with obstructive hydrocephalus with features of raised ICP, cranial nerve dysfunctions or cerebellar symptoms due to brainstem compression. Preoperatively history of regurgitation of fluids, choking on food, change in voice may suggest involvement of lower cranial nerves with loss of protective airway reflexes.

Figure 2: Posterior fossa tumor.

14 Surgical excision of a posterior fossa tumor is usually done in the prone position with the lateral and sitting positions being other alternative positions. Appropriate care while giving these positions must be taken. While resecting tumors involving the brainstem or around it, arrhythmias and hemodynamic fluctuations may occur and should be immediately notified to the surgeon. Tissue handling and retraction should be stopped till normalization of hemodynamic parameters occurs.

Extubation may be deferred and ventilator support provided if intraoperative course had multiple hemodynamic changes, injury to lower cranial nerves or expected postoperative respiratory insufficiency.

Supratentorial Tumors

Supratentorial tumors include craniopharyngiomas, gliomas, pituitary adenomas, choroid plexus papillomas and cerebral tumors (Figure 3). Craniopharyngiomas require detailed preoperative endocrine evaluation including pituitary, thyroid and adrenal functions as hypothalamic–pituitary–adrenal axis may be impaired necessitating perioperative hormone replacement therapy and corticosteroid supplements.

Common findings are hypernatremia with dilute urine. Replacement with antidiuretic hormone (ADH) substitute desmopressin [1-deamino-8-D-arginine vasopressin (DDAVP)] is often necessary. Anticonvulsants should be provided.²⁸ Fluid intake should match the urine output to prevent dehydration and should be primarily devoid of excess sodium load. Hence, 0.45% NS/RL alternatively can be used, till patient is able to take orally.

Figure 3: Craniopharyngioma.

Craniofacial Surgeries

15The anesthesiologist must understand the multiple problems occurring during complex craniofacial surgeries that are existent or may arise during the prolonged procedure and thereafter.

Craniosynostosis or premature fusion of one or more cranial sutures occurs in 1 per 2,000 live births.²⁹ It may be associated with other congenital anomalies. Apert’s syndrome and Crouzon’s syndrome are two of the more common syndromes involving coronal sutures (Figure 4).³⁰ Indications for surgery include increased ICP, airway compromise, proptosis and visual deterioration or cosmetic needs.³¹

Preoperative assessment should include identifying airway difficulties with cervical vertebral anomalies, limb anomalies and difficulty of venous access, speech and communication problems, cardiac, renal or urogenital anomalies and any evidence of raised ICP. Midface anomalies can cause airway obstruction and difficult mask ventilation. Adequate quantities of blood products should be cross-matched, and possibility of postoperative ventilator support needs to be explained to parents.

Inhalational technique with sevoflurane using a soft seal mask is commonly chosen for induction due to anticipated upper airway obstruction even under light planes of anesthesia and difficult intubation.

Figure 4: Craniosynostosis in a Crouzon’s syndrome child.

16 Reinforced orotracheal tubes are used, ensuring optimal positioning in trachea, firmly fixed and a pharyngeal pack is inserted. In difficult airway, fiberoptic technique, either awake or under GA may be needed. Submental intubation can be considered as an option to tracheostomy for procedures involving extensive facial oseotomies. Intraoperative problems include massive blood loss, prolonged surgery involving extensive tissue dissection, hypothermia, VAE and electrolyte and coagulation abnormalities. Blood loss should be meticulously replaced with fresh packed red blood cells to prevent hyperkalemia. Fresh frozen plasma and platelet transfusions are often needed to prevent coagulopathy. Most children can be extubated postoperatively if intraoperative course is uneventful and blood loss is adequately replaced. In patients with prolonged surgery, unstable hemodynamics, airway edema and difficulty in securing the airway at the start delayed tracheal extubation and postoperative ventilator support are needed.

Post-surgery facial edema is a common occurrence and patient should be nursed in head-up position.

Encephalocele

These children pose challenges to the anesthesiologist for intubation due to the presence of the lesion itself or other associated craniofacial anomalies (Figure 5). With either frontal or occipital encephalocele, the anesthesiologists have to intubate the patient in a suboptimal position while taking care to prevent accidental rupture of the lesion.

Figure 5: Frontal encephalocele with bilateral facial clefts. Note positive transillumination suggestive of cerebrospinal fluid content.

17Increase in ICP during induction also increases the size of encephalocele as more brain tissue protrudes out. Hence, attempts should be made to decrease ICP. Anesthesia management is otherwise similar to craniosynostosis, though in most cases reconstruction is not as extensive. Postoperative CSF rhinorrhea may occur following repair of frontal encephalocele.

Vascular Anomalies

Arteriovenous Malformations

An arteriovenous malformation (AVM) is a congenital intraparenchymal cluster of arterial-venous communications. Large symptomatic high-flow AVMs may present with congestive cardiac failure and associated systemic problems especially in neonates.³² In older children hydrocephalus, hemorrhage and neurological deterioration may be commonly seen.³³

The patient may present with symptoms related to increased ICP, seizures, migraine-like headaches or a “steal syndrome” manifesting as a progressive neurological deficit or related to local pressure effects. Intraoperative blood loss may be large and rapid, necessitating readily available blood in the operating room. Induced hypotension in such patients may produce ischemia in adjacent brain tissue and may also lead to venous thrombosis.

Moya Moya Disease

Moya Moya disease is a progressive vaso-occlusive disease, affecting the intracranial vessels, primarily the internal carotid artery causing ischemic stroke, headache and occasionally seizures and involuntary movements.³⁴ Children rarely may present with intracerebral hematomas or visual impairment. Surgery is needed to facilitate revascularization. The goal of anesthesia is to maintain normocarbia and avoid hypocarbia. Children should be adequately premedicated with good anxiolysis in order to prevent crying that causes hyperventilation. Anesthetic techniques should avoid hypotension, dehydration and hypothermia to maintain cerebral perfusion through small collateral vessels.³⁵ Inhalational anesthetics isoflurane and sevoflurane may cause cerebral steal phenomena by causing cerebral vasodilatation of normal region and diverting blood away from ischemic regions.

Epilepsy Surgeries

Epilepsy accounts for 4–10% of all pediatric neurological disorders.^36,37 Advances in neuroimaging and EEG have been able to accurately localize the source of 18 seizure actively, and hence definitive neurosurgery to treat this epileptic focus is now increasingly practiced.

History of epilepsy etiology, type, pattern and frequency of seizures, current antiepileptic treatment and control of seizures with it should be asked. Children on antiepileptic treatment like sodium valproate, carbamazepine and ethosuximide may be suffering from the side effects of these medicines like hematological abnormalities, coagulopathy, hepatic dysfunction that should be checked preoperatively. ECG and echocardiography should be performed in such patients and any other patients suspected to have cardiac abnormalities. The procedure may involve the placement of cortical mapping electrodes after craniotomy to identify epileptogenic focus, followed by excision of it in the same or a different sitting. The eloquent cortex also needs to be mapped out for identifying limits of safe resection in cases where the focus is close to the sensory or motor cortex.

Sevoflurane offers practical advantages for induction of anesthesia in uncooperative child and is commonly used. Propofol is also epileptogenic in low doses, but in anesthetic doses, it suppresses seizure activity. So, in children with intravenous access, propofol 2–4 mg/kg or thiopentone 5–7 mg/kg may be used. Use of peripheral nerve stimulator is recommended. If motor area is to be identified, neuromuscular blockade needs to be withheld. Anesthesia is usually maintained with inhalational agents with or without nitrous oxide.

In case of older cooperative children, an awake craniotomy with scalp nerves block for excision of the epileptic focus may be undertaken. Preoperatively rapport must be established with the child. Procedural sedation is commonly provided using dexmedetomidine,³⁸ propofol, midazolam, fentanyl or remifentanil with child breathing spontaneously and alert, obeying for at the time of cortical stimulation.

Another alternative is the asleep-awake-asleep technique, where GA is facilitated by supraglottic airway device till craniotomy and dural opening. Then child is awakened, supraglottic airway device is removed and surgeons proceed with resection under neurological monitoring. No anesthetic agents or medication with a potential to alter the EEG recording should be used. Once completed, child is anesthetized again and airway is secured for closure of dura and cranium. Problems include issues with airway management, brain swelling if child coughs or bucks or inadequate depth of anesthesia.

Meningomyelocele and Other Spinal Surgeries

Vertebral defects may be associated with hydrocephalus, Chiari malformation and other congenital anomalies of other systems. Open meningomyeloceles are 19 normally repaired in first week of life. Careful attention should be provided to airway management, intravenous fluids, body temperature, intravenous access and monitoring.³⁹ For induction and intubation, the baby should be carefully placed so as not to compress the meningomyelocele using appropriately positioned doughnut ring behind the back. Very large lesions may need intubation to be done in lateral position. High vagal tone in patients with Chiari malformation can lead to bradycardia during laryngoscopy and intubation due to brainstem compression.⁵ Children with spina bifida are prone to latex allergy and anaphylaxis.^40,41 All such children and should be managed in latex free environment to prevent sensitization.

Tethered spinal cord becomes apparent as the child grows with increasing scoliosis or progressive neurological deficit. To prevent or minimize damage to nerve roots during surgery for detethering, somatosensory evoked potential (SSEP) and motor evoked potential (MEP) monitoring may be used intraoperatively. Neuromuscular blocking agents should be avoided intraoperatively when MEPs are to be used. Inhalational anesthetic agents in higher doses, hypothermia, hypercarbia and spinal cord ischemia suppress both SSEP and MEPs.

Major bleeding can be anticipated in surgeries to correct scoliosis, resection of spinal tumors and spinal AVMs. Inappropriate positioning with increased abdominal venous pressure can further exacerbate the bleeding. Tranexamic acid with its antifibrinolytic properties has been shown to be effective in reducing the blood loss.⁴² Spinal cord perfusion pressure must be maintained by keeping stable hemodynamics and minimizing external compression. Intraoperative monitoring of spinal cord function using SSEP and MEP has been a standard of care in patients at the high risk of cord ischemia.

Postoperative pain relief may be provided using surgically placed epidural catheter or systemic opioids and nonsteroidal anti-inflammatory drugs combination.

CONCLUSION

Pediatric patients presenting for neurosurgical procedures have distinct neuroanatomy and neurophysiology and hence they should not be treated as small adults. Thorough preoperative evaluation with documentation of preoperative neurological deficits and their extent is required. Potential comorbidities should be identified and their anesthetic implications must be considered before planning appropriate anesthesia technique specific for the proposed procedure. Main goals of anesthesia include avoiding further neurological injury, providing optimum surgical condition and prompt emergence. Anticipation and prompt management of perioperative problems are essential for good outcome.

REFERENCES

Bissonette B, Armstrong DC, Rutka JT. Pediatric neuroanesthesia. In: Albin MS (Ed). Textbook of Neuroanesthesia with Neurosurgical and Neuroscience Perspectives. New York, NY: McGraw Hill; 1997. pp. 1177–240.

Dunn LT. Raised intracranial pressure. J Neurol Neurosurg Psychiatry. 2002; 73 (Suppl 1): i23–7.

Weigand C, Richards P. Measurement of intracranial pressure in children: A critical review of current methods. Dev Med Child Neurol. 2007; 49: 935–41.

Krass IS. Physiology and metabolism of brain and spinal cord. In: Newfield P Cottrell JE (Eds). Handbook of Neuroanaesthesia. Lippincott Williams and Wilkins; Philadelphia: 2007. pp. 3–22.

Rath GP, Dash HH. Anaesthesia for neurosurgical procedures in paediatric patients. Ind J Anaesth. 2012; 56: 502–10.

McClain CD, Soriano SG. Principles of pediatric neurosurgery. In: Matta BF Menon DK Smith M (Eds). Core Topics in Neuroanesthesia and Neurointensive care. Cambridge University Press; Cambridge: 2011. pp. 205–21.

Udomphorn U, Armstead WM, Vavilala MS. Cerebral blood flow and autoregulation after pediatric traumatic brain injury. Pediatr Neurol. 2008; 38: 225–34.

Pryds O. Control of cerebral circulation in the high risk neonate. Ann Neurol. 1991; 30: 321–9.

Soriano SG, Rockoff MA. Neuroanesthesia. In: Albright AL, Pollack I (Eds). Principles and Practice of Pediatric Neurosurgery. Thieme; New York: 2008. pp. 1213–29.

McClain CD, Soriano SG. The central nervous system: Pediatric neuroanesthesia. In: Holzman RS, Maneuso TJ Polaner DM (Eds). A Practical Approach to Pediatric Anesthesia. Lippincott Williams and Wilkins; Philadelphia: 2008. pp. 177–214.

McKenna MC, Gruetter R, Sonnewald U, Waagepetersen HS, Schousboe A. Energy metabolism of the brain. In: Siegel G, Albers RW, Brady S, Price D (Eds) Basic Neurochemistry: Molecular, Cellular and Medical Aspects. Oxford: Elsevier Academic Press; 2006. pp. 531–57.

Patel PM, Drummond JC. Cerebral physiology and the effects of anesthetic drugs. In: Miller RD (Ed). Miller’s Anesthesia. Churchill Livingstone; Philadelphia: 2010. pp. 305–40.

McClain CD, Soriano SG, Rockoff MA. Pediatric neurosurgical anesthesia. In: Cote CJ, Lerman J, Anderson BJ (Eds). A Practice of Anesthesia for Infants and Children. Elsevier; Philadelphia: 2013. pp. 510–32.

Slater P, Gupta K. Etomidate and injection pain in children. Br J Anaesth. 2007; 98: 545–52.

Rath GP, Bithal PK, Chaturvedi A, Dash HH. Complications related to positioning in posterior fossa craniectomy. J Clin Neurosci. 2007; 14: 520–5.

Cucchiara RF, Bowers B. Air embolism in children undergoing suboccipital craniotomy. Anestheiology. 1982; 57: 338–9.

Gale T, Leslie K. Anaesthesia for neurosurgery in the sitting position. J Clin Neurosci. 2004; 117: 693–6.

Williams EL, Hart WM Jr, Tempelhoff R. Postoperative ischemic optic neuropathy. Anesth Analg. 1995; 80: 1018–29.21

Kamming D, Clarke S. Postoperative visual loss following prone spinal surgery. Br J Anaesth. 2005; 95: 257–60.

Haisa T, Kondo T. Midcervical flexion myelopathy after posterior fossa surgery in the sitting position: Case report. Neurosurgery. 1996; 38: 819–21.

Porter JM, Pidgeon C, Cunningham AJ. The sitting position in neurosurgery: a critical appraisal. Br J Anaesth. 1999; 82: 117–28.

Garne E, Loane M, Addor MC, Boyd PA, Barisic I, Dolk H. Congenital hydrocephalus--prevalence, prenatal diagnosis and outcome of pregnancy in four European regions. Eur J Paediatr Neurol. 2010; 14: 150–5.

Rath GP, Prabhakar H, Bithal PK, Dash HH, Narang KS, Kalaivani M. Effects of butorphanol and fentanyl on cerebral pressures and cardiovascular hemodynamics during tunneling phase for ventriculoperitoneal shunt insertion. Middle East J Anesthesiol. 2008; 19: 1041–53.

Singh GP, Prabhakar H, Bithal PK, Dash HH. A retrospective analysis of perioperative complications during intracranial neuroendoscopic procedures: Our institutional experience. Neurol India. 2011; 59: 874–8.

Fabregas N, Craen RA. Anaesthesia for endoscopic neurosurgical procedures. Curr Opin Anaesthesiol. 2010; 23: 568–75.

Adelson PD, Bratton SL, Carney NA, Chesnut RM, du Coudray HEM, Goldstein B, et al. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents. Resuscitation of blood pressure and oxygenation and prehospital brain-specific therapies for the severe pediatric traumatic brain injury patient. Pediatr Crit Care Med. 2003; 4: S12-S18.

Godoy DA, Di Napoli M, Rabinstein AA. Treating hyperglycemia in neurocritical patients: benefits and perils. Neurocrit Care. 2010; 13: 425–38.

Ghirardello S, Hopper N, Albanese A, Maghnie M. Diabetes insipidus in craniopharyngioma: Postoperative management of water and electrolyte disorders. J Pediatr Endocrinol Metab. 2006; 19 (Suppl 1): 413–21.

Friedhoff RJ. Anesthesia for pediatric craniofacial surgery. Finnanest. 2000; 33: 387–9.

Koh JL, Gries H. Perioperative management of a patient with craniosynostosis. Anesthesiol Clin N Am. 2007; 2: 465–81.

Mallory SU. Craniofacial and neurosurgery. In: Bingham R, Lloyd-Thomas A, Sury M (Eds). Hatch & Sumner’s Textbook of Paediatric Anaesthesia. Boca Raton, FL: CRC Press; 2007. pp. 563–84.

Burrows PE, Robertson RL. Neonatal central nervous system vascular disorders. Neurosurg Clin N Am. 1998; 9: 155–80.

Sinha PK, Neema PK, Rathod RC. Anesthesia and intracranial arteriovenous malformation. Neurol India. 2004; 52: 163–70.

Parray T, Martin TW, Siddiqui S. Moyamoya disease: A review of the disease and anesthetic management. J Neurosurg Anesthesiol. 2011; 23: 100–9.

Baykan N, Ozgen S, Ustalar ZS, Dagçinar A, Ozek MM. Moyamoya disease and anesthesia. Paediatr Anaesth. 2005; 15: 1111–5.

Alizadeh Taheri P, Naseri M, Lahooti M, Sadeghi M. The life time prevalence of childhood seizures. Iranian J Publ Health. 2009; 38: 68–73.

Freidman MJ, Sharieff GQ. Seizures in children. Pediatr Clin North Am. 2006; 53: 257–77.

Ard J, Doyle W, Bekker A. Awake craniotomy with dexmedetomidine in pediatric patients. J Neurosurg Anesthesiol. 2003; 15: 263–6.

Hamid RK, Newfield P. Pediatric neuroanesthesia. Neural tube defects. Anesthesiol Clin N Am. 2001; 19: 219‑28.

Cremer R, Kleine-Diepenbruck U, Hoppe A, Bläker F. Latex allergy in spina bifida patients–prevention by primary prophylaxis. Allergy. 1998; 53: 709–11.

Cremer R, Kleine-Diepenbruck U, Hering F, Holschneider AM. Reduction of latex sensitisation in spina bifida patients by a primary prophylaxis programme (five years experience). Eur J Pediatr Surg. 2002; 12 (Suppl 1): S19-S21.

Sethna NF, Zurakowski D, Brustowicz RM, Bacsik J, Sullivan LJ, Shapiro F. Tranexamic acid reduces intraoperative blood loss in pediatric patients undergoing scoliosis surgery. Anesthesiology. 2005; 102: 727‑32.

Chapter Notes

Anesthesia for Neurosurgical Procedures in Children

ABSTRACT

Editor’s Comment