Making Pediatric Neuroanesthesia Safer.

It a challenging task for a Neuroanaesthetist to do the tight rope walking of maintaining the homeostasis of the small baby and at the same time complying with to the demands of the surgery and the surgeon. With the advancement of surgical techniques and availability of safer anaesthetic drugs and equipments it is possible to provide anaesthesia to even premature babies. This article gives a comprehensive review of the anatomical and physiological differences between the adult and the pediatric population and the anaesthetic implications of the various neurosurgical disorders.

INTRODUCTION

It is a challenging task for a neuroanesthetist to maintain the homeostasis of the small baby while complying with the demands of the surgery and the surgeon. The era when anesthesiologist shied away from these children is gone. Today, we are willing to face the children with the most complicated pathology and not deprive them of the benefit of the surgeon’s knife.

To attain our goal, we have to meticulously delve first into the detailed anatomy, physiology, and complexity of the pathology of the child. Only then will we be entitled to handle them. Any lapse will invariably be catastrophic. No child should be handled by an anesthetist who does not have a full knowledge of the pathology of the child. This is the first and foremost word of caution for pediatric neuroanesthesia. A child is not a miniature adult. He/she is an entity in himself/herself. Therefore, all the parameters should be made available to the anesthetist. The notable variations in the context of neurosurgery are as follows:

Developmental considerations: Development of the central nervous system is incomplete at birth, and maturation continues till 1 year of age.

Cerebral blood flow (CBF): It is coupled tightly to metabolic demand and both increase proportionally immediately after birth.

Cerebral metabolic rate for oxygen (CMRO It is higher in children (5.2 mL/100 g/min) than in adults (3.5 mL/100 g/min); hence, they have less tolerance to hypoxia. Neonates have a lower CMRO2 (3.5 mL/100 g/min) with a relative tolerance to hypoxemia.[2]

Autoregulation: Range of autoregulation is narrow, between 20 and 40 mm Hg, in a normal newborn[3] as compared to that of an adult, in the range of 50–150 mm Hg. Sudden hypotension and hypertension at either end of the curve place the neonate at risk for cerebral ischemia and intraventricular hemorrhage.

Preoperative assessment and advice: Evaluation must include history and physical examination. Assessment of neurological status should include evidence of raised intracranial pressure (ICP), an age-specific Glasgow Coma Scale, and cranial nerve palsies.

Airway examination may be difficult in children.

History of snoring,[4] apnea, daytime somnolence, and stridor may be indicative of airway obstruction, which may be exaggerated after induction. Physical examination should include evaluation of the size and shape of head; gross facial features; size and symmetry of mandible; size of tongue; prominence of upper incisors; and range of motion in jaw, head, and neck.

An echocardiography is needed in case of murmurs.

Other preoperative concerns are the use of anticonvulsant therapy and its effect on neuromuscular functions.

The signs of dehydration and serum electrolytes should be assessed before surgery.

Laboratory investigations conducted preoperatively should include complete blood count, renal and hepatic profile, coagulation studies, and blood grouping and cross matching. In cases of pituitary tumors, endocrine evaluation should be conducted.

INTRAOPERATIVE MANAGEMENT

Preoperative fasting: Generally followed as 2 h for clear liquids, 4 h for breast milk, and 6 h for formula and solid food.

Premedication: Preoperative anxiety needs to be addressed in the pediatric patients. Sedatives and narcotics should be avoided in all patients suspected to have increased ICP.

Induction: The goal of induction is to avoid an increase in ICP. Induction can be performed by inhalation technique if patient does not have an intravenous (IV) cannula in situ. This will avoid the raised ICP associated with crying and struggling. A nondepolarizing muscle relaxant is then administered to facilitate tracheal intubation. Children at risk for aspiration should undergo a rapid sequence induction with cricoid pressure.

Airway management: There are some basic anatomical differences between children and adults, which are as follows:

Prominent occiput

Larger tongue

U-shaped and floppy epiglottis

A more anterior and cephalad larynx, C3-4 in children and C5-6 in adults

Smallest diameter at the cricoid ring

There is a debate regarding the use of cuffed versus uncuffed tubes in pediatric patients. Cuffed endotracheal tubes can be used provided the cuff pressure is checked regularly.

Armored tubes are preferred in the prone position because they do not kink, preventing pressure injury to the tongue.

In case of an anticipated difficult airway, gadgets such as a Bullard laryngoscope, optical stylet, light wand, or a flexible fiber-optic scope can be used. These gadgets are available with an option for pediatric sizes and some even come with a neonatal size.

Vascular access: Adequate IV access is mandatory before the start of surgery. Vein finders are available. These work using infrared light-emitting diode. A minimum of two large-bore IV cannulas are sufficient for most craniotomies. The femoral vein is preferred for central venous access as it is more accessible during cranial surgery; also, it does not impede venous drainage and avoids the risk of pneumothorax associated with subclavian catheters.

Maintenance of Anesthesia: Anesthesia is maintained either with volatile agents with minimum alveolar concentration of <1 or with total IV anesthesia. Nitrous oxide should be avoided because its use can lead to increases in CBF and CMRO2. It also increases the volume of gas-filled spaces, which increases the potential for raised ICP in pneumocephalus after surgery.[5] Relaxants should be withheld when assessment of motor function is carried out during surgery on the spinal cord.

Fluid management: The goal is to maintain normovolemia and hemodynamic stability. Hyperglycemia worsens reperfusion injury so glucose-containing fluids are generally avoided. Hypoosmolar fluids should be avoided. Normal saline is the most common crystalloid used, is mildly hyperosmolar, and prevents cerebral edema. Rapid transfusion of normal saline at 60 mL/kg can be associated with hyperchloremic acidosis. Craniotomies can cause significant blood loss; prior estimation of the patient’s blood volume is essential in determining the amount of allowable blood loss and the time to transfuse blood.

In neonate and premature infants, the danger of hypoglycemia should be borne in mind and blood glucose should be closely monitored along with a glucose infusion at 5–6 mg/kg/min.

Raised ICP due to brain edema can be managed initially with head elevation and hyperventilation. If these maneuvers fail, mannitol can be given at a dose of 0.25–1.0 g/kg IV. This agent helps to raise serum osmolality by 10–20 mOsm/kg. Furosemide at a dose of 0.1 mg/kg can be used to decrease ICP.

Analgesia: Pain in a child is often inadequately assessed and treated. Unmanaged pain can lead to anxiety and stress, and in the long-term, this can impact on the psychosocial health and development of a child.

There are numerous myths such as neonates do not feel much pain due to the immaturity of the nervous system or anesthesia itself will reduce pain without any need for other analgesics. All children including neonates need analgesics. Multimodal analgesia with acetaminophen and nonsteroidal anti-inflammatory drug combination is seen to decrease the need for opioid analgesics.

Pharmacological methods of pain relief: Some of the most commonly used drugs are as follows:

Not recommended in children <6 months. Dose: 300 μg, 1 mg/kg 8 hourly PO/PR; maximum daily dose, 3 mg/kg or 150 mg.

Any patient requiring a morphine infusion with complex medical or surgical needs will require management in an intensive care unit (ICU).

Children with opioid infusions should be managed in the ICU with adequate monitoring.

INTRAOPERATIVE MONITORING

Routine intraoperative monitoring can be done with the use of capnography, pulse oximetry, electrocardiography (ECG), temperature, and arterial blood pressure. Urethral catheterization is needed for prolonged procedures, in patients requiring mannitol or with diabetes insipidus.

A central venous catheter is sometimes required for rapid fluid administration, vasoactive drugs, and for treatment of venous air embolism (VAE).

Some centers use precordial Doppler ultrasonography to detect VAE.[6]

Neurophysiological monitoring can be used to detect any neurological injury. The modalities for monitoring include electroencephalography, somatosensory evoked potentials, motor evoked potentials, brainstem auditory evoked potentials, and transcranial Doppler.

Positioning

The general principles to be followed while positioning are maintaining adequate ventilation, avoiding venous congestion, and avoiding complications related to improper positioning. Proper protection of the eyes from cleaning solutions as well as padding of pressure points should be ensured. Access to IV lines as well as visualization of the child under surgical drapes should be possible.

Supine position: In this position, the head is most commonly turned to one side. The endotracheal tube should be fixed on the nondependent side of the mouth to prevent loosening of the adhesive tape used to fasten the tube.

Excessive rotation of the head should be avoided to prevent occlusion of the internal jugular vein.

Prone position: Excessive neck rotation or flexion should be avoided, and pressure on the abdomen should be avoided to prevent vena caval compression and bleeding from the epidural veins. Pressure on eyes should be avoided to avoid postoperative visual loss.

Sitting position: This position should be used in patients above 4 years of age for exploration of the posterior fossa and cervical spine surgery. This position is associated with complications such as cardiovascular instability, VAE, mid-cervical flexion myelopathy, and macroglossia. Lateral position is rarely used with ipsilateral posterior lesions or cerebellopontine angle tumors.

Emergence: The goals are prompt awakening for early assessment of neurological functions and hemodynamic stability. Straining on the tube and coughing should be avoided to prevent rise in ICP and bleeding.

The trachea is extubated after the patient responds to command or an infant or toddler opens their eyes. Some anesthesiologists might prefer to extubate the trachea when the patient is still deeply anesthetized if there are no contraindications such as loss of airway reflexes, preoperative poor condition, and intraoperative catastrophe.

POSTOPERATIVE MANAGEMENT

Pediatric neurocritical care has emerged as a highly specialized clinical discipline in recent times. Postoperative mechanical ventilation might be required in surgeries that interfere with cranial nerve nuclei and brainstem function with depressed respiratory drive.

Hemodynamic support: Even in very small preterm babies, dopamine and epinephrine can be used to support systemic pressure and restore CBF [Table 1].

Table 1

Cerebral blood flow according to age

It is prudent to closely monitor electrolyte levels in the postoperative period to prevent hyponatremia-induced seizures.

Pain control and sedation present unique challenges in the management of pediatric neurosurgical patients. The ideal agent should be short-acting or reversible agent.

The mainstay of sedation in pediatric ICU patients remains a combination of narcotic and benzodiazepine administered through continuous infusion. Neuromuscular blockers may be needed to maintain the patient on mechanical ventilation.

Anesthetic management in specific conditions

Neonatal emergencies: Neonatal surgeries are generally performed on an emergency basis, which lead to an increase in morbidity due to undiagnosed congenital anomalies and persistence of the transitional circulation in premature neonates.

Hydrocephalus and shunt: Hydrocephalus is the most common problem in pediatric neurosurgical group. The conditions such as hemorrhage (intraventricular or subarachnoid hemorrhage in the neonate), congenital problems (aqueductal stenosis), trauma, infections, and tumors (especially posterior fossa) can lead to hydrocephalus. Most common surgical procedure conducted is ventricular drain or ventriculoperitoneal shunt placement. There is a risk of pulmonary aspiration once feeding begins. Anesthesia-related problems include difficulty in head positioning for intubation due to an enlarged head and hydration maintenance. The complications such as bradycardia, other arrhythmias, hypothermia, and also VAE during shunt placement can occur. Patients should be observed carefully in the postoperative period due to the risk of aspiration [Figure 1].

Figure 1

Hydrocephalus

Craniofacial abnormalities: These abnormalities are an array of developmental errors, quite a few of which are amenable to surgery. The different syndromes are associated with a plethora of associated abnormalities and merit special examination.

Craniosynostosis is the premature fusion of one or more cranial sutures. Single-suture craniosynostosis usually occurs in healthy children. Multiple-suture disease occurs as part of syndromes such as Apert, Crouzon, or Pfeiffer [Figure 2].

Figure 2

Craniosynostosis

Anesthetic concerns are the following:

- Difficult airway if associated with syndromes.

- Sudden major blood loss—as surgery occurs at the nidus of physiological anemia at 2 and 6 months.

- VAE—risk during retraction of the scalp over the orbital ridge.

- Oculocardiac reflex—profound bradycardia during orbital manipulation.

- Positioning—it will vary with the procedure; care is needed to protect the eyes and to prevent excessive neck flexion and extension.

Blood transfusion may be required postoperatively if oozing from surgical site continues. Possible airway compromise due to facial edema might defer extubation.

Intracranial tumors: Brain tumors are the most common solid tumors of childhood. A majority of intracranial tumors occur in the posterior fossa [Figure 3].

Figure 3

Giant occipital encephalocele

Some unique challenges are as follows:

Intracranial hypertension due to obstructive hydrocephalus

Pressure responses to laryngoscopy, during Mayfield head-pin fixation

Sitting position and its related problems

Posterior fossa tumors posing an anesthetic challenge due to the involvement of the vital structures and their derangement during surgery. The brainstem and lower cranial nerves, especially vagus manipulation, may produce bradycardia and hypotension, which are indicators of the damage to the vital medullary centers. The surgeon has to be warned of such incidents

Craniopharyngiomas are the most common perisellar tumors and may need endocrine assessment and replacement both pre- and postoperatively. Steroid replacement is required because the integrity of the hypothalamic–pituitary–adrenal axis may be uncertain. In case diabetes insipidus develops, hypovolemia and electrolyte imbalance should be corrected before induction of the patient. Pharmacological treatment may be required if hypovolemia is not corrected with fluids.

Epilepsy surgery: This surgery is a tightrope walking, necessary in patients with medically intractable seizures owing to congenital disorders, birth trauma, or vascular malformations. Anesthetic concerns include perioperative seizures and the effects of anticonvulsant drugs. If intraoperative electrocorticographic (ECoG) monitoring is planned, sedatives and anticonvulsants should be withheld for 48 h preoperatively.[7] Inhaled anesthetics should be avoided during ECoG recordings. Nitrous oxide should be avoided until the dura is opened because nitrous oxide causes rapid expansion of air cavities and results in tension pneumocephalus.

Trauma: Head injury in children may give rise to intracranial hematoma or diffuse axonal injury and edema. Intracranial compliance and autoregulation may be impaired. Basic life-support algorithms should be applied to ensure patient airway, breathing, and circulation. Immobilization of the cervical spine is necessary to avoid cord injury. Hemodynamic stability should be maintained with adequate fluid resuscitation. Sometimes, children with head trauma may present with depression of ST segment in the ECG.[8] These ST-T changes are due to the sympathetic hyperactivity associated with raised ICP. Anesthetic goal is to prevent secondary injuries such as hypoxia, hyperthermia, hypotension, hypoglycemia, and hyperglycemia. Blood should be crossmatched and made available during evacuation of extradural hematoma.

Spine surgery: The primary indication for laminectomies in pediatric patients is spinal dysraphism. These patients might have a history of meningomyelocele (MMC) and other corrective surgeries. Latex allergy may be an associated complication. Patients might have anaphylaxis that requires identification and management with fluid and vasopressors.

Neuromuscular disorders: Pediatric muscle disorders encompass myasthenic syndromes, myotonias, dystrophies, and mitochondrial myopathies. In myasthenic syndromes, caution during the administration of muscle relaxants is prudent; also, respiratory system may be highly sensitive to the depressant effect of anesthetics. In the case of known cases, tailoring of anesthetics can be done, but in an undiagnosed patient, management of such a patient may be difficult. Vigilance is essential. In all boys, a family history of neuromuscular disease or adverse reaction to anesthesia should provoke suspicion. Developmental milestones should be assessed and examination must assess tone and include an inspection for calf hypertrophy. If any suspicion arises, screening of creatine kinase may guide management. The absence of family history in a hypotonic child with other organ system involvement should provoke suspicion of mitochondrial myopathy, in which case preoperative lactate levels may be useful. It is possible that the greatest challenge lies in managing the undiagnosed patient who may develop a catastrophic reaction to a chosen anesthetic.[9]

Meningomyelocele and encephalocele: Failure of fusion of embryogenic neural tube causes herniation of meninges with (MMC) or without (meningocele) neural elements in any level of the spinal cord. When defect occurs in cranium, it is called encephalocele [Figures 4–6].

Figure 4

Meningocele

Figure 6

Encephalocele

MMC is usually associated with Arnold–Chiari malformation (ACM) (most commonly Type II) and hydrocephalus.[10]

Pseudomeningocele

These children may present with features of brainstem compression such as apnea, vocal cord palsy causing stridor,[11] autonomic instability, and abnormal respiration.

Following are the anesthetic concerns:

- Positioning: difficulty in positioning due to the swelling can be overcome by placing it in a doughnut.

- Electromyography monitoring to identify functional nerve roots is done intraoperatively [Figure 7].

Figure 7

Intraoperative neural monitoring

- Sudden blood loss.

- VAE.

- Children having an increased risk of latex allergy, although it is rarely encountered in Indian context.[10]

Children with posterior encephalocele are intubated commonly in lateral decubitus position, or with the swelling supported by a doughnut, and even by placing the child’s head beyond the edge of the table, supported by an assistant.

Intraoperative hemodynamic disturbances are commonly encountered during encephalocele repair. Apart from having a strong vagal tone, children with Chiari malformation may experience bradycardia during laryngoscopy and intubation due to compression of the brainstem. Cardiac arrest is also observed.

Neuroendoscopy and neuroradiology: Minimally invasive endoscopic surgery has entered the pediatric neurosurgical arena. Anesthetic considerations are the same as in other neurological procedures. In procedures such as the endoscopic third ventriculostomy and choroid plexus coagulation for treatment of obstructive hydrocephalus, complications such as arrhythmias and neurogenic pulmonary edema may occur. These are due to the manipulation of the floor of the third ventricle.

Neuroradiological procedures in children may require sedation or general anesthesia. General anesthesia is typically used in patients who are uncooperative or have coexisting medical problems, to minimize motion artifact and for potentially painful procedures, such as intravascular embolization of vascular lesions.[12] Because of the distance between the patient and the anesthesia provider, it is suitable to secure the airway in the radiology suite. In case of hybrid procedures consisting of angiography, embolization and surgical resection require a multidisciplinary team approach between radiologist, neurosurgeons, and intensivists.

A crisis management plan should also be there in case of any untoward incidents.

CONCLUSION

Pediatric neuroanesthesia balances the difficulties of an immature nervous system and the physiology of a child. Surgeries have evolved into complex undertakings, which require detailed and thorough perioperative management. Training in pediatric anesthesia can be of great assistance in the evolution of a pediatric neuroanesthesiologist. Advances in anesthetic agents, techniques, and monitoring aim to improve perioperative outcomes in this set of children. As the future beckons, a set of trained anesthesiologists will likely provide safer anesthesia to neurosurgical patients.

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Nil.

Conflicts of interest

There are no conflicts of interest.