Anesthesia for Endoscopic Third Ventriculostomy in Children.

Neuroendoscopy has established itself as a routine neurosurgical procedure in pediatric population. To have an uneventful smooth perioperative course, it is important for anesthesiologist to know about the key steps, possible complications, and specific anesthetic requirements. Among neuroendoscopies, endoscopic third ventriculostomy is the commonly performed one.

INTRODUCTION

Endoscopic neurosurgical procedures are becoming more frequent in the pediatric population.[1] The advantage of this technique is that it allows intracranial intervention with minimal damage to healthy brain tissue. Also from the surgeon's perspective, it provides better visualization of the intracranial structures. Initially, neuroendoscopy was performed exclusively for endoscopic third ventriculostomy (ETV), for the treatment of obstructive hydrocephalus. However, it is being successfully employed recently in many types of neurosurgical procedures, either as a primary approach or as an adjunct.[2] For the past many years, it has proved its worth as a surgical approach for tumor biopsy or resection, cyst fenestration, and removal, evacuation of intraventricular hemorrhage and plexus coagulation.

Although most of these procedures have become established as a routine for the last 10–20 years, reports in the literature about basic anesthesia concepts for this particular technique is sparse.[3] Although a minimally invasive technique, with low morbidity and mortality even in patients younger than 24 months, a few complications have been reported in the literature.[4] For successful conduct of anesthesia, one should be aware of these problems as well as the basic surgical requirements. Among neuroendoscopic procedures, ETV is a commonly performed and well-established technique for noncommunicating hydrocephalus. It is also recommended in cases of shunt malfunction or infections.

Interestingly, the first endoscopic procedure in neurosurgery was performed by Victor Lespinasse about 100 years ago. He is reported to have used a cystoscope to fulgurate the choroid plexus in two infants.[5] Twelve years later, Walter Dandy repeated the same procedure.[6]

PROCEDURE

Basically, ETV involves establishing a connection between third ventricle and prepontine subarachnoid space, fenestrating the floor of third ventricle. This allows the flow of cerebrospinal fluid (CSF) from the third ventricle to basal subarachnoid space while bypassing the aqueduct.[7] After ventriculoscope insertion, the procedure can be viewed on a video screen.

Ventriculoscope is inserted through a frontal burr hole to the right (2–3 cm from midline) and in front of coronal suture, directed to the third ventricle Figure 1. Bupivacaine 0.25% with vasoconstrictor is infiltrated for analgesia and to reduce bleeding. Optimal surgical access is achieved in supine or semi-sitting with the head flexed so that the burr hole can be conveniently located at the apex. This will also help to minimize the loss of CSF.[8] Absolute immobility of the patient is required for the safe passage of scope through the brain tissue.[8] Measuring volume of fluid infused and ensuring adequate efflux is important to prevent any rise in intracranial pressure (ICP). Because of close proximity of the third ventricle to midbrain, any acute distension has the potential to precipitate cardiac arrhythmias.[9] Ringer Lactate at body temperature is the most commonly used irrigation fluid.

Figure 1

Direction of scope from frontal burr hole to the third ventricle.

PATIENTS

Usual clinical presentation is with features of hydrocephalus or for revision surgery with an in situ shunt. Associated congenital malformations such as meningomyelocele, congenital cardiopathies are also reported.[10]

PREOPERATIVE PLANNING

Dehydration and electrolyte abnormalities if present need to be corrected before surgery. Patient's neurological status is noted before accepting the case. Associated bulbar palsy and sleep disturbance are also noted. Patients are at higher risk of urinary tract infections or impaired renal function as a part of multisystem congenital syndromes. Usual surgical time is 20–60 min. Since rapid postoperative neurological assessment is desirable, agents such as high dose narcotics which can cause prolonged postoperative sedation need to be avoided.[11]

ANESTHETIC TECHNIQUE

If the child has got an intravenous (IV) line, induction with propofol or thiopental is ideal. But in children without IV access, inhalational induction is the logical option and is acceptable.[111213] Sevoflurane has got an edge over other inhalational agents in the context of pediatric practice, because of its well-tolerated odor which facilitates smooth induction. Incidence of laryngospasm, airway irritability, and breath holding is less with sevoflurane. However, the use of nitrous oxide is discouraged because of elevations in ICP, expansion of ventricular air bubbles and exacerbation of symptoms in the event of venous air embolism.[1415] For maintenance of anesthesia, both total IV anesthesia involving remifentanyl and volatile agents like sevoflurane have been described. One potential problem noted in pediatric patients is the incidence of hypotension and bradycardia with bolus doses of remifentanyl. This can be avoided by starting it as infusion at the time of induction and titrating with response. Inhalational agents can be used in <1 minimum alveolar concentration wherein there will not be any considerable increase in cerebral blood flow (CBF).[16] Care of thermoregulation is critical, especially in small children. Large exchange of irrigation fluid and wetting of surgical drapes expose the child to the risk of life threatening perioperative hypothermia.[17] Use of thermal blanket and warm irrigation fluids or fluid warmer is strongly advocated.

The largest possible catheter should be used to establish peripheral venous line, and access should be ensured throughout the procedure. The aim of IV fluid administration is to maintain normovolemia. In general, there is no requirement for blood transfusions. Routine and emergency drugs must be labeled and kept. Proper postoperative analgesia can be ensured by combinations of paracetamol and low dose opiates, without affecting postoperative neurologic evaluation.[13] Eyes should be protected from external pressure and surgical cleaning solutions. While positioning the child, care must be taken to ensure adequate ventilation and avoidance of venous congestion.

INTRAOPERATIVE MONITORING

A consensus on standard monitoring requirements has not yet established in the literature. Basic monitoring includes electrocardiography, pulse oximetry, capnography, temperature, and urine output monitoring. There are many authors who recommend invasive blood pressure monitoring by indwelling arterial catheter in all patients, irrespective of their age.[18] Abrupt changes in CBF due to changes in ICP is possible during the procedure. Transcranial Doppler is the fastest and most reliable method to detect any fluctuations in CBF due to changes in ICP.[19] It has got high sensitivity to changes in CBF. However, practical objections restrict it is routine use in neuroendoscopic procedures even though many consider it as a routine monitor in neuroendoscopy. Use of ICP monitoring and the methods employed is another debatable point. Even though several strategies to ICP monitoring are described, measuring through the rinsing channel of the endoscope is preferred in literature.

COMPLICATIONS

Fatal complications described in literature are rare.[20] However, Injury of the basilar artery is the most feared intraoperative complication. Artery is located under the floor of third ventricle and can be subjected to trauma by the catheter tip.[21] This can lead to massive intraventricular and subarachnoid hemorrhage, hemiparesis, and midbrain damage. Manipulation of delicate structures around the third ventricle (hypothalamus and brain stem) can occasionally lead to intraoperative bradyarrhythmias, hypotension, hypertension, and even cardiac arrest.[22] This procedure can also result in reduction of cerebral perfusion or even ischemia secondary to an increase in ICP. Other reported neurological complications are paralysis of III and VI nerves, delayed awakening, transitory mental confusion, headache, loss of memory, infection, convulsions, and pneumocephalus. Hypothermia is a potential complication that can result in delayed awakening and disordered coagulation. However, some of the commonly observed postoperative complications such as vomiting and respiratory problems are not specific to the procedure. Overall, a good long-term outcome after ETV is between 70% and 80% in most case series.[23] With expertise, complication rates are bound to come down. In fact it is now accepted as a therapeutic option ahead of shunt revision in cases of obstructive hydrocephalus.[24]

CONCLUSIONS

With improvements in technology, neuroendoscopy in pediatric population are now routinely performed in more and more centers. It is important for anesthesiologists to understand the particularities associated with this procedure to effectively navigate the patient in the perioperative settings. It is imperative to document extent of pre-existing neurological impairment and associated congenital defects. Any fluid and electrolyte abnormalities should be corrected before taking up for procedure. Attention should be given to problems specific to pediatric age group such as hypothermia and fluid overload. Absolute intraoperative immobilization, cardiovascular stability, and rapid recovery for neurological assessment are perceived anesthetic goals. Any rapid increase in ICP must be prevented, detected, or quickly managed. Fortunately, fatal complications are rare.

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Conflicts of interest

There are no conflicts of interest.