Perioperative management of patients with spina bifida

Learning objectives.

By reading this article, you should be able to:

• •Describe the classification, epidemiology, embryology and aetiology of spina bifida (SB).
• •Relate the multisystemic manifestations of SB relevant to the anaesthetist.
• •Detail aspects of perioperative care unique to patients with SB.

Key points.

• •Patients with spina bifida (SB) have multisystem comorbidity and may require surgery throughout their lifetime
• •Involvement of the multidisciplinary team, including neurosurgery, orthopaedics, urology, occupational therapy and physiotherapy, enables optimal management.
• •Patients with SB pose a diverse range of challenges to the anaesthetist, such as neonatal anaesthesia, emergency neurosurgery, complex limb reconstruction and major spinal surgery.
• •Preoperative evaluation may include assessing neurological status, including documenting sensory deficits or the presence of a CSF shunt; and screening for obstructive sleep apnoea.
• •Challenges include care in a latex-free environment, difficult venous access, appropriate positioning and avoidance of pressure areas.

Spina bifida (SB) is a congenital neural tube defect (NTD) that results from incomplete spinal column closure during embryonic development. Neural tube defects are among the commonest birth defects. The incidence of SB is six in every 10,000 births (0.06%) in the UK.¹ This has declined with folic acid supplementation and varies significantly across different populations.^2,3 Ten-year survival now exceeds 80%.⁴ Patients with SB may require surgery throughout their lifetime, from neonatal closure to cerebrospinal fluid (CSF) diversion procedures, urological intervention and major orthopaedic surgery. Spina bifida results in multisystem comorbidity which poses a diverse range of challenges to the anaesthetist.

Classification

Classification was first described by Cameron and Willis in 1962 who proposed four subtypes: spina bifida occulta, meningocele, myelomeningocele and myelocele.^4,5 Neural tube defects include cranial defects such as anencephaly. Spina bifida includes open and closed NTDs affecting the spinal cord.⁵ The most important distinction for anaesthetists is between closed and open SB.

Spina bifida occulta means ‘hidden split spine’ and is also known as a closed spinal dysraphism.⁶ It is a closed NTD resulting from failure of fusion of the posterior vertebral bodies. The defect is enclosed by skin and the neural tissues are not exposed. There may be a pigmented patch of hair or sacral dimple at the site of the dysraphism. Tethered cord may be associated, but its incidence in otherwise normal children with a simple sacral dimple is as low as 0.13%.⁷ Clinical manifestations vary greatly; patients may have no sequelae or may have symptoms secondary to spinal cord involvement including back pain, neurogenic bladder dysfunction and musculoskeletal involvement.⁸

Spina bifida aperta or open spina bifida is characterised by exposed neural tissue and includes meningocele and myelomeningocele. Myelomeningocele, the most significant form of SB, is a fluid-filled sac containing spinal cord tissue that protrudes through the vertebral column (Fig. 1). This incomplete closure at the distal cord leads to dysfunction of bladder, bowel and lower limb sensory and motor deficits. Meningocele is a variant where the cord is not contained within the herniated sac.⁹ Spina bifida aperta presents with a visible lesion at birth or can be diagnosed antenatally on ultrasound. Exposed neural tissue renders patients susceptible to further damage and infection. They therefore require rapid evaluation and treatment.

Fig 1.

Open myelomeningocele in a neonate demonstrating a fluid-filled neural sac containing spinal cord.

Embryology and pathophysiology

Spina bifida occurs as a result of failure of fusion of the neural folds. The neural tube is formed between the third and sixth week of gestation. Neurulation begins when the neural plate lateral edges, which form from the outermost layer of the embryo, elevate to form neural folds. These neural folds then fuse and give rise to the neural tube. This occurs in the cervical regions and then extends in both directions.

It is believed that this opening in the neural tissues prevents accumulation of fluid and pressure in the cranial vesicles. Absence of distension causes a Chiari II malformation, small posterior fossa and cerebral disorganisation.¹⁰ Spina bifida results from a combination of genetic and environmental factors. The prevalence is increased in those with fetal trisomy 13 and 18. Maternal diabetes, obesity, exposure to toxins, medications (antiepileptic drugs) and hyperthermia have also been implicated.^11,12 The introduction of folate supplementation has significantly reduced the incidence of NTDs with a relative risk of 0.31 reported in a Cochrane Review.¹³

Diagnosis

Diagnosis can be made antenatally with ultrasound or postnatally on clinical examination. Fetal anomaly scanning is highly sensitive. Third ventricle dilatation and small head circumference are common features.¹⁴ Distinct ultrasound indicators include the ‘lemon sign’ (inward concavity of the frontal bones) and the ‘banana sign’ (an anteriorly effaced cerebellum). The diagnostic specificity of the lemon sign is almost 100%. Detection of any of these necessitates further examination of the brain and spine. The degree of ventriculomegaly should be assessed as it aids prediction of the need for postnatal ventriculoperitoneal (VP) shunt insertion.¹⁵ Abnormalities of the bony spine, disruption of skin contours, or a cystic sac may be present. Fetal MRI scanning may also be performed to achieve diagnostic certainty or to better define the level of the NTD.¹⁶ Postnatal diagnosis is more common with spina bifida occulta or in patients where no screening has occurred.

Clinical features

There is a wide spectrum of clinical manifestations, the most common being neurological dysfunction. The neurological sequelae are related to the level of the lesion. Patients with a low sacral lesion may be asymptomatic whereas lumbar or thoracic lesions can cause significant impairment.

Neurological abnormalities are usually present at birth and are caused by neural tissue exposure in utero. Clinical signs may develop over time where patients have hydrocephalus or tethered cord. The Chiari II malformation is present in nearly all patients with a myelomeningocele. It is characterised by downward displacement of the cerebellar tonsils and medulla. Lack of distension of the embryonic ventricular system leads to a normal sized cerebellum developing in a small posterior fossa. It causes obstructed flow of CSF resulting in hydrocephalus (Fig 2, Fig 3). These anomalies in fetal brain development are believed to cause deficits in cognitive function and are also responsible for increased mortality.¹⁰

Fig 2.

Axial computed tomography slice demonstrating hydrocephalus with characteristically enlarged lateral ventricles.

Fig 3.

Sagittal magnetic resonance image demonstrating a Chiari II malformation with a caudally displaced cerebellum and associated hydrocephalus.

Spinal cord manifestations depend on the lesion level. Thoracic myelomeningocele can result in significant neurological impairment and patients are frequently wheelchair bound. Lumbosacral myelomeningocele is the most common. It has a varied clinical presentation. Some patients can achieve full ambulation but others may have significant disabilities. The degree of motor function is influenced by complications such as hydrocephalus, musculoskeletal issues and pressure sores. Although deficits in myelomeningocele are usually severe, certain segments of the spinal cord may retain partial function, allowing for voluntary control of isolated movements or limited sensation.^17,18 Sensation and pain perception vary greatly. Afferent pathways can be disrupted, leading to absence of pain perception, but spinal reflexes can be preserved. The level of myelomeningocele also affects bladder and bowel function.

Brainstem dysfunction is caused by Chiari malformation in most. Neonates may present with vocal cord dysfunction leading to stridor, swallowing difficulties or apnoea, in isolation or in symptom complexes. Apnoeic episodes can be central or obstructive.¹⁹ The incidence of hydrocephalus is around 80–90% in myelomeningocele and 60–70% in all SB patients.^17,20 It is associated with Chiari II malformation.²¹ It can be present at birth or occur as a consequence of closure. Hydrocephalus is the leading cause of neurological disability in SB. Presenting features range from subtle cognitive defects to severe neurological impairment. Rapid increase in head circumference, vomiting, irritability, somnolence and sun setting eyes indicate acutely raised intracranial pressure (ICP).²⁰ This is a neurosurgical emergency and warrants rapid investigation to prevent worsening neurological injury.²¹ In older patients, headaches, cognitive disturbances, behavioural changes and cerebellar signs can indicate evolving hydrocephalus. Treatment of hydrocephalus is traditionally with a VP shunt, which allows venting of CSF above a set pressure. Shunt malfunction should be considered in anyone presenting unwell. Its risk is between 25% and 40% in the first year and 5% per year thereafter.²² An endoscopic third ventriculostomy (ETV) is an alternative treatment. An opening is created in the floor of the third ventricle allowing CSF flow to the basal cisterns. An ETV may be preferred when the obstruction to flow is below the level of the third ventricle.²³ Learning disability and cognitive challenges are commonplace as children develop. Patients with myelomeningocele are affected to a greater extent.^24,25 Full neuropsychological assessment facilitates early recognition and intervention to optimise cognitive development and independence.²⁶ There is also an increased risk of seizure disorders in patients with SB.²⁷

Urinary tract complications present in 91% of patients.²⁸ Spinal cord dysfunction leads to incontinence or retention. Vesicoureteric reflux can lead to renal injury. Early urological assessment is advocated. Clean intermittent catheterisation may prevent dysfunction. Anticholinergics lower bladder filling pressures, and minimise reflux. Bladder augmentation can be considered in patients with high urinary tract pressures despite optimal medical management.^29,30

Bowel dysfunction occurs in 87% of patients with SB, significantly affecting quality of life and emotional wellbeing.²⁸ The level of the lesion determines presenting symptoms. Those above the conus medullaris result in increased sphincter tone and constipation. Lesions at or below the conus lead to sphincter flaccidity and incontinence. Management includes fibre intake, laxatives, enemas and manual disimpaction. Transanal irrigation and surgical intervention (antegrade continence enema) can be used in resistant cases and are associated with increased quality-of-life scores.³¹ An individualised approach to managing bowel and bladder function is essential for long-term quality of life and independence.

Orthopaedic complications significantly affect mobility, function and gait. Scoliosis and kyphosis may affect respiratory function adversely. Hip and foot deformities such as hip dislocation, talipes equinovarus (clubfoot) and congenital vertical talus (rocker bottom foot) significantly affect walking. Rotational deformities such as tibial torsion can impair gait and balance. Management necessitates a multidisciplinary approach. Physiotherapy, orthotics and surgical corrections are integral parts of treatment, with the aim of optimising mobility, function and quality of life.³²

Pressure ulcers affect those with limited mobility and sensory impairment developing over bony prominences. In a United States registry 15.6% of patients with myelomeningocele experienced a pressure ulcer in the preceding 12 months.²⁸ Untreated, pressure ulcers can lead to severe infection and osteomyelitis and have severe effects on life expectancy and healthcare costs. Prevention includes skin checks, adequate nutrition, pressure mattresses and regular repositioning. A multidisciplinary team approach including dressings, antibiotics and debridement is needed.²⁴

Cardiorespiratory complications are multifactorial. Brainstem dysfunction can cause apnoeas, vocal cord palsies, poor cough and atypical responses to hypoxia and hypercarbia. Scoliosis may precipitate restrictive lung disease. Immobility and poor cough lead to frequent lower respiratory tract infections. Sleep-related breathing disorders are common. Right ventricular dysfunction can develop. Autonomic dysreflexia may be present with thoracic myelomeningocele or brainstem anomalies.

Perioperative management

Children can present for multiple neurosurgical procedures including antenatal or postnatal closure, VP shunt insertion and revision, Chiari II release, tethered cord release and MRI. Other typical procedures include urological, lower limb orthopaedic and scoliosis surgery (Table 1).

Table 1.

Preoperative, intraoperative and postoperative key points. ABG, arterial blood gas; OSA, obstructive sleep apnoea; PFTs, pulmonary function tests.

Preoperative	•Motor and sensory level •Hydrocephalus •Shunt presence and function •Chiari II malformation and bulbar palsy •Epilepsy •Restrictive lung defects •Spo2, ABG, PFTs •Functional assessment •Echocardiography if limited mobility •Baseline renal function •Care with creatinine interpretation (low body mass)
Intraoperative	•Positioning difficulties •Videolaryngoscopy to limit movement of the neck •Endobronchial intubation risk •Lung protective ventilation •Cautious fluid management •Consider invasive arterial pressure monitoring •Temperature monitoring •Difficult i.v. access •Consider analgesia requirements •Risk of autonomic dysreflexia •Care with nephrotoxic drugs
Postoperative	•Multimodal analgesia •Caution with doses of opioids in OSA •Anticipate longer recovery time

Preoperative assessment

For elective procedures, patients should ideally attend a consultant-led preoperative assessment clinic. This permits identification and optimisation of any associated comorbidities. A thorough history, examination and appropriate investigation is necessary. Neurological status should be assessed and any sensory or motor deficits, presence of hydrocephalus or prior intervention should be documented. A CSF diversion procedure is preferable before major elective surgery. Chiari II malformation predisposes patients to risk of brainstem herniation. Compliance with medication and seizure frequency should be determined for those with epilepsy.

Airway assessment should consider potential difficulty with positioning which may be because of relative macrocephaly, kyphoscoliosis, contractures or pressure areas. Caution with excess neck extension should be considered in those with Chiari II. Respiratory assessment should include assessment of bulbar function and any restrictive lung defects. If present, baseline oxygen saturation, arterial blood gas and pulmonary function testing should be considered. These can help guide postoperative care.³³

Cardiovascular assessment should include baseline functional status and assessment of metabolic equivalents if practicable. If patients are wheelchair-bound, an echocardiogram should be considered. Presence of significant respiratory compromise should prompt investigation of right heart dysfunction. A history of bladder dysfunction should prompt evaluation of baseline renal function. Creatinine level should be carefully interpreted in the context of low muscle mass. Renal ultrasound may be performed in high-risk patients.

If notes are unavailable or detailed past medical history cannot be provided, neurosurgical review is recommended before urgent or elective procedures to assess the presence and functional status of or requirement for shunt.

Intraoperative management

Patients with SB require a latex-free environment to reduce the likelihood of developing latex allergy, the prevalence of which is as high as 64%.³⁴ Standard monitoring is recommended, and invasive arterial pressure monitoring considered for those with cardiorespiratory involvement. Core temperature should be monitored. Neurophysiological monitoring may be indicated for spinal surgery. Difficult i.v. access should be anticipated and ultrasound imaging available. Positioning should be optimised for airway management. Multiple pillows are helpful for patients with kyphoscoliosis, contractures and pressure sores. An appropriate shoulder roll aids head positioning with relative macrocephaly. Videolaryngoscopy prevents excessive neck movement. Endobronchial intubation may be more likely because of a relatively short trachea. Bilateral air entry should be ensured with early recourse to flexible bronchoscopy to assess tube position. Bulbar palsy, vocal cord paralysis and raised ICP may increase the risk of aspiration. This should be balanced against the risk of desaturation in those with impaired respiratory function when considering rapid-sequence induction of anaesthesia. Mechanical ventilation can be challenging in patients with significant restrictive lung defects. Low-normal tidal volumes should be targeted (around 6–7 ml kg⁻¹) to prevent excessive airway pressures and permissive hypercapnia is acceptable. While an increase in ICP should be a consideration, a functioning shunt is protective. Meticulous care and attention are required when positioning patients for surgery to prevent injury. Additional supports for limbs with contractures may be necessary. Fluid management in patients with cardiac dysfunction should be cautious. Drugs excreted by the kidney should be used with care in those with renal dysfunction. Neuromuscular blocking agents should be fully antagonised at the end of surgery.

The use of neuraxial anaesthesia is controversial and evidence is limited to case reports. There is thought to be an increased risk of spinal cord damage, even in SB occulta. This is attributable to abnormalities of the cord such as tethering, low lying conus, diastematomyelia or associated intra-spinal abnormalities such as cysts or tumours.³⁵ However, there are published case reports describing the performance of successful, uncomplicated neuraxial anaesthesia in patients with SB.³⁶ We would not recommend this approach unless general anaesthesia is completely contraindicated.

Postoperative considerations

A multimodal approach to analgesia should be used. Requirements may be reduced depending on the degree of sensation at the surgical site. NSAIDs may be contraindicated in renal dysfunction. Careful titration of opioids is recommended with respiratory dysfunction. Patients may require prolonged care in the post-anaesthesia care unit and supplemental oxygen or CPAP. Those with hydrocephalus or Chiari malformation should be monitored for an extended period for neurological deterioration.

Specific surgical procedures

Closure of a myelomeningocele

Meningomyelocele closure is usually performed within 72 h of birth and this presents challenges of both neonatal and neurosurgical anaesthesia. Discussion with neurosurgeons is imperative to determine the presence and severity of any hydrocephalus and whether a CSF diversion procedure will be performed simultaneously. The closure strategy should be elucidated. Little blood loss can be expected with primary closure. If a local advancement tissue flap is planned, blood should be cross-matched and invasive arterial monitoring prepared. Significant blood loss can occur in this situation. Primary closure can affect ventilation with significant increases in airway pressures observed. Clear communication with the surgeon is vital. Suture tension should be reduced if airway pressure is incompatible with extubation. Postoperative care should be in a neonatal high dependency unit. Respiratory effort should be carefully observed. Patients are generally nursed prone with close monitoring for increased ICP, the risk of which is significantly increased post-closure. Analgesia should be titrated using an appropriate neonatal pain score with consideration given to sensation at the repair site because of the increased risk of postoperative respiratory events.

Posterior fossa decompressive craniectomy for Chiari II release

The surgical strategy is to increase the diameter of the foramen magnum and decompress the posterior fossa. Neck manipulation should be avoided as this may precipitate brainstem compression. Prone positioning and intraoperative neck flexion necessitate careful placement and fixation of the tracheal tube to minimise the risk of endobronchial migration. As with any paediatric posterior fossa surgery, blood loss can be rapid and haemostasis difficult to achieve. Blood products should be available. Intravenous access appropriate for massive transfusion and a fluid warmer should be prepared. Decompression of CSF may cause brainstem traction, which can lead to bradycardia and possible asystole. It is important to alert the neurosurgical team during periods of haemodynamic instability, which may improve with altering of manipulation. An infusion of adrenaline (epinephrine) should be available and central venous access strongly considered.

Tethered cord release

Tethered cord syndrome is attachment of the filum terminale to inelastic structures. This limits movement of the cord within the canal which can result in stretching of and damage to the cord. It is associated with SB and can cause progressive motor and sensory dysfunction. Diagnosis is confirmed with MRI. It is corrected with division and release of the filum. Surgery is only performed if clinical signs or symptoms of deterioration are present. Neurophysiological monitoring may be used; neuromuscular blocking agents and volatile anaesthetic agents. should be omitted. MAP should be controlled to maintain an age-appropriate spinal cord perfusion pressure. A prolonged procedure and significant patient exposure necessitate careful temperature management. The dura is opened during tethered cord release so postoperative CSF leakage is possible.³⁷

Spinal surgery

Scoliosis affects at least 30% of patients with SB. Posterior spinal fusion carries a higher risk of complications than in patients without SB. Rates of infection, instrumentation failure and non-union are higher with up to 50% of patients experiencing a major complication.³⁸ An anterior approach may necessitate one-lung ventilation. Patients and their parents should be counselled about this increased risk.

Kyphectomy, or removal of kyphotic vertebrae, is particularly high risk. Kyphosis occurs in up to 20% of SB patients. It can cause significant difficulty with upright positioning, sitting and lying supine. Patients are predisposed to pressure ulcers at the site of kyphotic vertebrae. Kyphectomy is performed to improve functional sitting position and reduce the risk of pressure ulcer.³⁹ Kyphectomy presents numerous risks both intraoperatively and after surgery. Patients with significant thoracic kyphosis are likely to have restrictive lung defects. Lung and right heart function should be assessed before surgery to determine fitness for surgery. The procedure carries a risk of significant blood loss and haemodynamic instability. There is also a significant risk of decreased or loss of spinal cord signals. A local protocol for management of this event is useful and should include anaesthesia factors such as target MAP, haemoglobin and corticosteroid use in addition to surgical steps such as reversal of immediate antecedent intervention. After surgery, the risk of wound breakdown, infection and failure of instrumentation is significant. Multiple returns to the operating theatre have been reported.⁴⁰ Excellent analgesia is essential to facilitate early transfer and positional change. ICU admission is strongly advised.

Advances in the management of SB

Fetoscopic surgery has led to significant improvement in neurological sequelae and quality of life. These advances come after the landmark Management of Myelomeningocele Study (MOMS) in 2011. This compared open prenatal (<26 weeks) repair of myelomeningocele to postnatal closure. It was stopped early for efficacy. Prenatal repair reduced the need for CSF shunting (68% vs 98%), hindbrain herniation and improved motor score and mental development. However, open prenatal surgery was associated with an increased risk of preterm delivery and uterine dehiscence.⁴¹

Complications associated with open prenatal repair led to the exploration of fetoscopic and hybrid (hysterotomy and trocar insertion) repair. These have demonstrated non-inferiority with regards to shunt placement and neurological function. Percutaneous fetoscopic repair was associated with higher rates of premature rupture of membranes (91% vs 36%, P<0.01) and preterm birth (96% vs 81%, P=0.04) compared with open repair, whereas fetoscopic repair via maternal laparotomy reduced preterm birth. The rate of dehiscence and leakage from the myelomeningocele repair site was higher after both types of fetoscopic surgery (30% vs 7%, P<0.01), while the rate of uterine dehiscence was higher after open repair (11% vs 0%, P<0.01).41, 42, 43

Anaesthesia for these procedures is complex and provides the unique challenge of dual patient anaesthesia. General anaesthesia is used. Maintenance is with volatile anaesthesia to promote uterine relaxation and is supplemented with remifentanil for both maternal and fetal analgesia and immobility. Tocolysis is with an oxytocin antagonist, glyceryl trinitrate or increased volatile and is continued after surgery. Fetal analgesia and neuromuscular blocking agents can be given via i.m. injection for open procedures.⁴⁴

Conclusions

Spina bifida is a multifaceted condition. Patients present for surgery throughout their lifetime. A thorough understanding of the systems affected and a holistic approach are required. Advances in surgical treatment are improving quality of life and changing the nature and timing of our interaction with these complex patients.

Declaration of interests

The authors declare that they have no conflicts of interest.

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.

Biographies

Sean Hartigan FCAI is a specialist registrar in anaesthesia. He is currently undertaking his training module in paediatric anaesthesia at Children's Health Ireland at Temple Street, the national referral centre for paediatric neurosurgery and spinal surgery in patients with spina bifida.

Bill Walsh FCAI FJFICMI is a consultant paediatric anaesthetist at Children's Health Ireland (CHI) at Temple Street, the national paediatric neurosurgery centre, and previously at the National Orthopaedic Hospital Cappagh, a tertiary centre for paediatric lower limb reconstruction. He is also an assistant professor in the School of Medicine, University College Dublin and the Irish representative on the council of the Association of Paediatric Anaesthetists of Great Britain and Ireland.

Matrix codes: 1A01, 2D02, 3D00