Anesthesia for Neural Tube Defects

This chapter discusses the anesthetic and perioperative concerns of pediatric patients presenting for repair of all NTDs and not restricted to SCM alone. Besides inherent risks of anesthesia and surgery in the pediatric population, special considerations pertaining to disease, non-neurological complications, and perioperative management of associated systemic anomalies will be discussed in this chapter.

Preanesthetic Evaluation

To minimize infection of the exposed cord and consequent sepsis, open NTDS are repaired as early as possible within the first few days of life.2 The preoperative visit is the first interaction of an anesthesiologist with a patient. A neonate should be evaluated for all possible anomalies during this visit. It is the only time for an anesthesiologist to build a rapport with older children, especially toddlers. For planning good anesthesia technique, a thorough history and physical examination to look for neurological and systemic abnormalities is a must. A proper history and examination can rule out involvement of other systems. In the presence of specific symptoms, required investigations should be requested and documented. Patient physiology should be optimized to as normal as possible without undue delay in surgical procedure.

Systemic Evaluation

NTDs are frequently associated with other anomalies, including heart, esophagus, kidneys, brain, limbs, and anal canal. Congenital heart disease (atrial and ventricular septal defects, anomalous pulmonary venous circulation, dextrocardia, patent ductus arteriosus, tetralogy of Fallot, bicuspid aortic valve, coarctation, and hypoplastic left heart syndrome) may be present in up to 37% patients with NTDs.² History of recurrent chest infections, cyanotic spells, and abnormal auscultation of heart along with X-ray findings suggestive of cardiac involvement mandate cardiac evaluation by an expert. Preoperative echocardiography is advised to assess cardiac function in these patients. Anorectal malformations, hydronephrosis, tracheoesophageal fistula, hydroureter, malformed ureters, solitary kidney, horseshoe kidney, neurogenic bladder, exstrophy of bladder, undescended testes, hydrocele, omphalocele, Meckel’s diverticulum, and inguinal hernia are the other common problems seen in these children. Genitourinary anomalies are seen in up to 10 to 30% of the patients.² Presence of facial cleft, kyphoscoliosis, and chest wall malformation may pose problems during intubation, positioning, and ventilation of these patients and make perioperative period challenging. Other neurological anomalies like Arnold–Chiari II malformation, hydrocephalus, microcephaly, corpus callosum agenesis, Dandy–Walker malformation, Meckel syndrome, microgyria, porencephalic cyst, arachnoid cyst, and vitreous degeneration commonly accompany NTDs. Infants with hydrocephalus and Arnold–Chiari malformation are prone to cervical cord compression during extension of spine and may develop severe bradycardia at the time of laryngoscopy and intubation. According to a retrospective analysis of 135 children with MMC, hydrocephalus was the most common association (67.4%), followed by Chiari-II malformation (58.4%). Renal abnormality was present in 9% of cases and 24.4% of children had scoliosis. Two infants (1.5%) presented with inspiratory stridor. Two children (1.5%) suffered cardiac arrest; both had associated Chiari-II malformation and hydrocephalus. Postoperative ventilation was required in 8.9% of children, primarily due to inadequate reversal from neuromuscular blockade.²

Raised intracranial pressure (ICP) and preoperative drowsiness may contribute to delayed awakening after surgery. Lower cranial nerve palsies may result in aspiration pneumonia and prolonged ventilatory requirement. Serum electrolytes abnormalities, especially sodium and potassium, are commonly seen in patients with frequent vomiting episodes. If CSF shunt is present, its function should always be assessed before induction of anesthesia. Choice of anesthetic agent and perioperative course can be anticipated and properly planned with complete knowledge of patient profile.

Airway and Respiratory Evaluation

Securing airway is difficult in neonates and infants when compared to adults. It becomes even more difficult in the presence of midline swelling, large hydrocephalic head and facial clefts. Ventilation can be rendered difficult due to big nasal encephalocele. Patients with Arnold–Chiari have irregular control of ventilation, impaired chemical drive, and bilateral vocal cord paralysis. Such patients may present with apneic spells. Patients can suffer from aspiration pneumonia attributable to gastroesophageal reflux, absent gag and cough reflexes, or lack of oropharyngeal coordination.2 Short trachea is present in 36% of patients with MMC.² Postoperative mechanical ventilation should be anticipated in patients with abdominal muscle weakness and inefficient cough, causing decreased ability to clear secretions after prolonged surgery.² It should be discussed with guardians. Infants which are irritable, lethargic, and with altered consciousness may remain so postoperatively, and extubation plan may be decided accordingly.

Perioperative Investigations

Routine and specific investigations depending on the systems involved should be obtained. Baseline hemogram and leukocyte count are done if not done in the previous 1 month. Raised leucocyte count indicates an infected sac. Blood grouping and cross-matching are advisable in case of large defect, warranting perioperative blood transfusion. Adequate amount of blood and blood product should be arranged.

Chest X-ray is useful to rule out cardiomegaly in suspicious cases. It may also help to identify any evidence of aspiration. Air bronchogram is considered to see the length of trachea.2 Electrocardiography (ECG) and 2D echocardiography may help to delineate underlying cardiac anomalies. Additional studies should include coagulation profile and renal and hepatic function as per requirement.

Preanesthetic Preparation

Fasting instructions: When determining a suitable fasting period, both the amount and nature of foods ingested must be considered. Preoperative fasting guidelines recommended by American Society of Anesthesiologists (ASA) task force are shown in Table 14.1. For elective surgeries, pediatric patients should preferably be kept first in the list.²

Table 14.1 Fasting guidelines for pediatric patients
Ingested material	Minimum fasting period
Clear liquids	2 h
Breast milk	4 h
Infant formula	6 h
Nonhuman milk	6 h
Light meal	6 h
Fried foods, fatty foods, or meat	≥ 8h

Fig. 14.1 Patient head positioned over horseshoe.

Fig. 14.2 Patient under anesthesia in prone position.

Table 14.2 Anesthetic concerns in patients with NTDs
Stage of evaluation	Related concerns
Preoperative evaluation	•Complete workup to rule out associated anomalies •Evaluation and documentation of neurological deficits •Size and location of defect and its effect on anesthesia and positioning •Complete airway and respiratory assessment •Cardiovascular assessment •Evaluation for need of postoperative ventilation •History of latex sensitivity •Appropriate preoperative investigations
Intraoperative concerns	Proper positioning •To avoid direct pressure on defect •Avoid excessive extension during intubation •Check tracheal tube position, and prevent kinking and endobronchial migration •Ensure patient safety in prone position Anesthetic technique to ensure •Adequate depth of anesthesia •Hemodynamic stability •Intraoperative neuromonitoring •Rapid wakening at the end of procedure Avoid •Hypothermia •Hypovolemia •Hyponatremia •Hypercarbia
Postoperative considerations	•Intensive nursing care •Analgesia •Hypothermia prevention

Abbreviation: NTDs, neural tube defects.

Premedication: The requirement of type of premedication depends on the neurological status and the age of patient. Baby may be shifted carefully to or in the lap of a nurse. The swelling should be handled with gloved hands and cotton pads. Toddler paranesthesia room can be equipped with toys and popular animation movies. Anxiolysis is seldom required for neonates; however, anxiolytics are essential in an infant to allay separation anxiety. Benzodiazepines are the preferred drugs. Oversedation may result in hypoventilation and augmentation of ICP, causing brainstem herniation, especially in patients with Arnold–Chiari malformation, so medication should be administered under strict supervision only.

■ Latex Sensitivity

The reported incidence of latex allergy and latex sensitization in patients with MMC is 10 to 73%.²^–² The potential reasons include contact to latex products during repeated bladder catheterizations, genetic propensity, and multiple surgical procedures. The manifestation of allergic reactions can be mild (tingling of the lips, facial swelling, and wheezing) to severe anaphylaxis with cardiovascular collapse. Children with a possibility for latex sensitivity and anaphylaxis should be managed in latex-free setting, and if anaphylaxis develop during surgery, latex allergy should be suspected. Removal of the latex, administration of fluid, and treatment for anaphylaxis like intravenous epinephrine, vasopressors, steroids, H1 and H2 histamine blockers should be administered, depending upon the symptomatology.²

OT Preparation

Hypothermia prevention: Thin skin, low fat content, exposure of large body surface area, cold irrigation fluid, skin preparation, prolonged wound exposure, general anesthesia (GA)-induced redistribution of heat from core to periphery, administration of intravenous (IV) fluid at room temperature, irrigation fluid, and dry anesthetic gases are major factors responsible for development of intraoperative hypothermia in the pediatric population. Premature patients with large lesions have inherent difficulty in maintaining body temperature. Hypothermia may cause delayed awakening from anesthesia, cardiac irritability, respiratory depression, increased pulmonary vascular resistance, and altered responses to intraoperative anesthetics and neuromuscular blocking agents.

The risk of hypothermia can be decreased by warming operating theatre ≥26° before shifting the patient to operating room. Using heated humidified inspired gases and warming all IV and irrigation fluids helps to minimize the heat loss. The patient’s limbs and uninvolved body area should be covered to maintain body temperature.2 Passive warming devices (cotton blankets, surgical drapes, plastic sheets, reflective composites, sleeping bags) or active warming devices (circulating water mattresses/garments, force air warmers, resistive heating devices, negative pressure water warming systems, and radiant heaters) can be used to keep the child warm.

Induction of General Anesthesia

Preparation of weight-calculated drugs, airway cart, pediatric breathing circuit, etc., should be ensured before arrival of the patient.

Proper positioning during induction of GA and surgery is of utmost importance, as neonates with hydrocephalus show a diminished response to hypoxia and increased susceptibility to postoperative apnea.² Any direct pressure on the uncovered neural placode adds to neural insult.² Infants with hydrocephalus and Arnold–Chiari malformation are more prone to cervical cord compression during extension for intubation. Positioning and airway management are specially challenging in case of large encephalocele. For induction, patient can be placed in supine or lateral position, depending on size and site of the defect. Foam cushion devices are also described for protecting the fragile sac from being compressed.² Additional padding beneath the shoulders and head may be needed if placing the defect in the middle of a “doughnut” causes pressure on the open defect.² Babies with large head can have their head dangling (well-supported by an assistant) over the edge of table for intubation purpose. Head dangling avoids pressure on the encephalocele sac² and attains proper positioning for intubation. Head can be placed over horseshoe head holder to avoid direct compression of the defect (Fig. 14.1). Chance of compression of the sac, and hence a raised ICP, can also be avoided by intubation in lateral position.²

Difficult airway should be anticipated in syndromic babies with abnormal facies. Preoxygenation with a nonlatex mask of appropriate size is advised. In patients with facial deformity, prevention of sac compression during mask ventilation is essential. Modification of mask ventilation can be used for it.²

Anesthesia Technique

The goal of anesthetic induction is to avoid hypoxia, hypercapnia, and volatile anesthetic-induced increases in cerebral blood flow, as all these factors may increase ICP. Other considerations are related to difficult positioning and associated anomalies and congenital malformations. The trachea may be intubated after the IV administration of a sedative-hypnotic and an intermediate acting nondepolarizing muscle relaxant. An IV induction with thiopentone or propofol is commonly practiced. However, in children without IV access or with difficult IV access, inhalational induction by facemask with sevoflurane is preferred to avoid crying and struggling.2 IV technique may be continued after IV access is secured. Succinylcholine should be avoided in patients with neurological deficit. The indication of awake intubation is unusual positioning and anticipated very difficult airway. An international consensus group and others have raised concerns about awake intubation until it is a life-threatening condition.² At the time of laryngoscopy and induction, children may develop bradycardia due to brainstem compression. Since short trachea has been described in children with MMC, it is essential to prevent endobronchial migration of tracheal tubes. After induction, the patient is made prone on an adequate-sized bolster, head is well-supported, and all bony points and eyes are padded. Abdomen should be free of any external compression (Fig. 14.2).