CHAPTER 173 Neuroanesthesia in Children
Preoperative Evaluation and Preparation
Preparation of pediatric patients for anesthesia and surgery is essential to minimize perioperative morbidity. Given the systemic effects of general anesthesia and the physiologic stress of surgery, an organ system review should be performed to anticipate potential physiologic derangements and coexisting disease states that may increase the risk for perioperative complications.1 Because some children are preverbal or do not fully understand their medical condition, their parents or primary caretakers should be carefully interviewed to obtain information regarding coexisting medical problems. A thorough review of the patient’s history can reveal conditions that may increase the risk for adverse reactions and identify patients who need more extensive evaluation or whose medical condition needs to be optimized before surgery. Certain medical problems may require that the anesthetic be modified (Table 173-1). There are also special perioperative concerns regarding children with neurological abnormalities (Table 173-2). Preoperative fasting is necessary to minimize aspiration of gastric contents during the operative procedure, guidelines for which are listed in Table 173-3.
TABLE 173-1 Common Perioperative Concerns in Infants and Children
| CONDITION | ANESTHETIC IMPLICATIONS |
|---|---|
| Congenital heart disease | Hypoxia and cardiovascular collapse |
| Prematurity | Postoperative apnea |
| Gastrointestinal reflux | Aspiration pneumonia |
| Upper respiratory tract infection | Laryngospasm and postoperative hypoxia or pneumonia |
| Craniofacial abnormality | Difficulty with airway management |
TABLE 173-2 Common Perioperative Concerns in Infants and Children with Neurologic Problems
| CONDITION | ANESTHETIC IMPLICATIONS |
|---|---|
| Denervation injuries | Hyperkalemia after succinylcholine |
| Resistance to nondepolarizing muscle relaxants | |
| Chronic anticonvulsant therapy for epilepsy | Hepatic and hematologic abnormalities |
| Increased metabolism of anesthetic agents | |
| Arteriovenous malformation | Potential congestive heart failure |
| Neuromuscular disease | Malignant hyperthermia |
| Respiratory failure | |
| Sudden cardiac death | |
| Chiari’s malformation | Apnea |
| Aspiration pneumonitis | |
| Hypothalamic/pituitary lesions | Diabetes insipidus |
| Hypothyroidism | |
| Adrenal insufficiency |
TABLE 173-3 Guidelines for Fasting before Surgery or Anesthesia
Closed-claim analysis studies have revealed that neonates and infants are at higher risk than any other age group for morbidity and mortality.2,3 Respiratory and cardiac-related events account for a majority of these complications. Given the urgent nature of neonatal neurosurgical procedures, a thorough preoperative evaluation may be difficult. Preoperative evaluation and laboratory tests should be tailored to the proposed neurosurgical procedure. Patients with suprasellar pathology should have thyroid function tests performed because hypothyroidism can lead to bradycardia and hypotension and prolong emergence from general anesthesia. The latter can mimic an adverse neurological event such as stroke or cerebral edema. Diabetes insipidus can be diagnosed by history and abnormal serum electrolytes. A complete airway examination is essential because some craniofacial anomalies may require specialized techniques to secure the airway.4 Congenital heart disease may not be detected immediately after birth. Therefore, echocardiography can be helpful in assessment of the heart, especially in a neonate, and a pediatric cardiologist should evaluate patients with suspected problems to help optimize cardiac function before surgery. Table 173-2 matches special concerns in pediatric patients with neurological problems. Subspecialists may be helpful to optimize the patient’s condition before surgery and assist in postoperative management.
The infant or child may not have the cognitive ability to rationalize the gravity of the situation. Patients and family members are usually frightened by the strange surroundings of the hospital and operating room, exposure to unfamiliar hospital workers, the possibility of painful stimuli, and the thought of separation from each other and treasured comfort objects. Therefore, the approach to a pediatric patient should take into account the patient’s developmental age. Table 173-4 lists the cognitive stages of pediatric patients and age-appropriate concerns.
TABLE 173-4 Preoperative Concerns in Pediatric Patients
| AGE GROUP | CONCERNS |
|---|---|
| Infants (0-9 mo) | None; separate easily from parents |
| Preschoolers (9 mo-5 yr) | Stranger anxiety, difficulty with parental separation |
| Grade school children (6-12 yr) | Fear of needles and pain |
| Adolescents (>12 yr) | Anxious about surgery and self-image |
Preoperative administration of sedatives before induction of anesthesia can ease the transition from the preoperative holding area to the operating room.5 Midazolam given orally is particularly effective in relieving anxiety and producing amnesia. Preoperative sedation should be withheld or administered only with close observation in patients with deteriorating findings on neurological examination or lethargy because it can induce respiratory depression and interfere with serial neurological examinations.
Intraoperative Management
Induction of Anesthesia
The patient’s neurological status and coexisting abnormalities dictate the most appropriate technique and drugs for induction of anesthesia. Generally, alert patients should be able to tolerate any type of induction technique. If intravenous (IV) access has not been established, general anesthesia can be induced by inhalation of sevoflurane and nitrous oxide with oxygen.6,7 This can be facilitated by having one parent present in the operating room during induction to help calm small children. Once the patient is unresponsive, the parent is escorted out of the operating room and IV access is rapidly established. A nondepolarizing muscle relaxant is then administered to facilitate intubation of the trachea. Despite the widespread use of inhaled induction in pediatric anesthesia, complications such as laryngospasm or vomiting may occur and lead to airway obstruction and hypoxia. Alternatively, if the patient has IV access, anesthesia can be induced rapidly with sedative-hypnotic drugs such as thiopental or propofol.
Airway Management
Anatomic differences between the pediatric and adult airway are primarily due to the size and orientation of components of the upper airway, larynx, and trachea. Neonates and infants have the greatest differences from adults in this respect. However, the configuration of the larynx becomes similar to that of adults after the second year of life. Table 173-5 highlights the major differences between pediatric and adult airway anatomy. An infant’s larynx is also funnel shaped and narrowest at the level of the cricoid, thus making this region the smallest cross-sectional area in the infant airway. This places the infant at risk for life-threatening subglottic obstruction secondary to mucosal swelling after prolonged intubation with a tight-fitting endotracheal tube. An endotracheal tube can also migrate into a mainstem bronchus if the infant’s head is flexed for a suboccipital approach to the posterior fossa or the cervical spine. Therefore, the anesthesiologist should auscultate both lung fields to rule out inadvertent intubation of a mainstem bronchus after the patient is positioned for the surgical procedure.
TABLE 173-5 Differences between Pediatric and Adult Airway Anatomy
| INFANT | ADULT | |
|---|---|---|
| Tongue | Relatively large | Normal |
| Epiglottis | Floppy, angled posteriorly | Firm, less posterior angle |
| Vocal cord angle | Inclined | Flat |
| Glottis | C3-4 level | C5 level |
| Cricothyroid membrane | Small | Large |
| Trachea | Mobile, posterior displacement into the thorax | Stationary, vertical descent into the thorax |
Because an immediate neurological examination is essential for assessment of the patient, the timing of tracheal extubation may be challenging after neurosurgical procedures. Infants, particularly those with a Chiari malformation,8 or older children after procedures in the posterior fossa9 may exhibit intermittent apnea, vocal cord paralysis, or other irregularities before resuming a stable respiratory pattern. Significant airway edema and postoperative obstruction can complicate prolonged prone procedures or those involving significant blood loss and large-volume replacement. Finally, preexisting pulmonary dysfunction, as in infants with bronchopulmonary dysplasia or older children with neuromuscular disease, may force delays in extubation because of respiratory insufficiency. In these cases, objective criteria and the presence of an air leak around the endotracheal tube with airway pressures less than 20 to 25 cm H2O will determine the appropriate timing of postoperative extubation.10 Lingual or supraglottic swelling may require direct laryngoscopy to assess the airway. Head-up positioning and gentle forced diuresis usually improve airway edema within 24 hours.
Maintenance of Anesthesia
The choice of anesthetic agents for maintenance of anesthesia has been shown to not affect the outcome of neurosurgical procedures.11 Table 173-6 lists commonly used anesthetic drugs. The most frequently used technique for neurosurgery consists of IV administration of the opioid fentanyl or sufentanil, along with inhaled nitrous oxide and low-dose isoflurane or sevoflurane. Remifentanil is a unique opioid that is rapidly metabolized by plasma esterases and characterized by rapid emergence from anesthesia.12,13 However, it is frequently accompanied by delirium and inadequate analgesia.14,15 Deep neuromuscular blockade is maintained during most neurosurgical procedures to avoid any patient movement. Patients receiving chronic anticonvulsant therapy require larger doses of muscle relaxants and narcotics because of induced enzymatic metabolism of these agents.16 Muscle relaxation should be withheld or not maintained when assessment of motor function during seizure or spinal cord surgery is planned.
| Inhaled Anesthetics |
|
Nitrous oxide |
Hemodynamic stability during intracranial surgery requires careful maintenance of the patient’s fluids and electrolytes. Given the risk for significant blood loss associated with many neurosurgical procedures, a hematocrit and prothrombin time/partial thromboplastin time should be obtained to uncover any insidious hematologic disorders. Typed and cross-matched blood should be ordered before all craniotomies. Small patients have a greater percentage (up to 25%) of their cardiac output directed toward the head.17 Fluid restriction and diuretic therapy may lead to hemodynamic instability and even cardiovascular collapse if sudden blood loss occurs during surgery. Therefore, normovolemia should be maintained throughout the procedure. Normal saline is commonly used as the maintenance fluid during neurosurgery because it is mildly hyperosmolar (308 mOsm/kg) and it theoretically attenuates brain edema. However, rapid infusion of a large amount of normal saline (30 mL/kg per hour) is associated with hyperchloremic acidosis.18 Table 173-7 provides guidelines for IV fluid administration in pediatric patients. Hyperventilation and careful patient positioning to maximize cerebral venous drainage can minimize brain swelling. Should these maneuvers fail, mannitol can be given at a dose of 0.25 to 1 g/kg intravenously. This transiently alters cerebral hemodynamics and raises serum osmolality by 10 to 20 mOsm/kg.19 However, repeated dosing can lead to extreme hyperosmolality, renal failure, and further brain edema. Furosemide is a useful adjunct to mannitol for decreasing acute cerebral edema and has been shown in vitro to prevent rebound swelling caused by mannitol.20 All diuretics interfere with the ability to use urine output as a guide to intravascular volume status.
TABLE 173-7 Guidelines for Maintenance of Intravenous Fluids in Infants and Children
| WEIGHT (kg) | MAINTENANCE FLUIDS PER HOUR |
|---|---|
| <10 | 4 mL/kg |
| 10-20 | 40 mL + 2 mL/kg for every kg between 10 and 20 kg |
| >20 | 60 mL + 1 mL/kg for every kg >20 |
