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Craig Sims, Dana Weber and Chris Johnson (eds.) A Guide to Pediatric Anesthesiahttps://doi.org/10.1007/978-3-030-19246-4_23

23. Pediatric Neuroanesthesia

Mairead Heaney^{1, 2}

(1)

Paediatric Critical Care Unit, Perth Children’s Hospital, Nedlands, WA, Australia

(2)

Department of Anaesthesia and Pain Management, Perth Children’s Hospital, Nedlands, WA, Australia

Mairead Heaney

Email: Mairead.Heaney@health.wa.gov.au

Keywords

Pediatric neuroanesthesiaCerebral perfusion pressure in childrenAnesthesia children traumatic brain injuryAnesthesia spina bifida

Despite the evolution of anesthetic and surgical techniques over time, the goals of pediatric neuroanesthesia remain unchanged—to provide effective anesthesia and analgesia, reduce intracranial pressure, maintain cerebral perfusion pressure, and to allow rapid recovery after surgery.

23.1 Anatomy

The child’s brain and central nervous system is the fastest growing organ in the body. As in adults, brain tissue and extracellular fluid occupy 80% of the intracranial compartment, and cerebrospinal fluid (CSF) and blood occupy 10% each. The brain can grow during infancy because the cranial suture lines are not fused. The child’s skull however, is pliable and incomplete, and offers less protection than an adult’s. The posterior fontanelle closes by the second month of life. The anterior fontanelle stays open until approximately 18 months and it allows assessment of intracranial pressure (ICP) or ultrasound imaging of intracranial structures. The child’s brain is incompletely myelinized, has a higher water content than an adult’s, and is more homogenous and susceptible to diffuse axonal injury and cerebral edema. The blood brain barrier is freely permeable to water, and rapid changes in plasma osmolarity greatly affect the water content of the brain.

23.2 Physiology

Compared with adults, neonates have lower, and children higher, cerebral blood flow (CBF) and cerebral metabolic oxygen consumption (CMRO₂) (neonate < adult < child) (Table 23.1). The pediatric brain is probably less tolerant to reduced cerebral blood flow than the adult brain. Cerebral autoregulation occurs, but the pressure limits of regulation are not known with certainty. In neonates and infants, the lower limit of autoregulation is closer to the baseline mean arterial pressure than in older children—a fall in neonatal blood pressure is likely to reduce cerebral blood flow.

Table 23.1

Differences between adult and pediatric brain blood flow

	Brain mass (% body weight)	Cerebral blood flow (mL/100 g brain tissue/min)	Percentage of cardiac output	CMRO₂ (mL/100 g/min)
Adult	2	55	15	3.5
Child	10	100	25	5.5
Term neonate	15–20	40		Lower than adult
Preterm neonate	15–20	12		Lower than adult

Intracranial pressure in neonates and infants is normally between 0 and 6 mmHg. In older children and adults, the range is between 13 and 15 mmHg. In infants, a gradual increase in intracranial volume will expand the head with only a small increase in ICP, such as with hydrocephalus. If volume rises rapidly, however, the non-elastic pericranium and dura mater means ICP rises rapidly, ultimately causing herniation of the brain stem through the foramen magnum. In infants, an increase in intracranial volume of only 10 mL results in a 10 mmHg increase in intracranial pressure, which is the reason children rapidly deteriorate after intracranial hemorrhage . The cerebral perfusion pressure is lower in younger children than adults (Table 23.4).

Keypoint

When intracranial pressure gradually rises in an infant, the fontanelles bulge, the suture lines open and the increase in ICP is accommodated. When intracranial pressure suddenly rises in an infant, the inelastic pericranium cannot suddenly stretch, and just as in adults, the ICP suddenly increases.

23.3 Pharmacology

The inhalational and intravenous anesthetics have broadly the same effects on cerebral blood flow and CMRO₂ in children and adults. All inhalational agents increase CBF and reduce CMRO₂. Low concentrations of isoflurane and sevoflurane (less than 1 MAC) with ventilation to maintain normocarbia minimally affect CBF and ICP. Propofol is a cerebral vasoconstrictor that reduces CBF and CMRO₂ while preserving autoregulation in both children and adults. Ketamine does not increase ICP when ventilation is controlled, has favorable effects on cerebral perfusion pressure and may have neuroprotective effects. Fentanyl and remifentanil have only minor effects on CBF and CMRO₂ in children and adults.

23.4 Pediatric Brain Tumors

Intracranial tumors are the second commonest childhood cancer after leukemia.

23.4.1 Background

Most pediatric brain tumors are primary tumors and more than half occur in the posterior fossa. The peak incidence is between 3 and 8 years of age. The commonest types in the posterior fossa are medulloblastoma, pilocytic (low grade) astrocytoma , glioma and ependymoma (Table 23.2). Supratentorial tumors are more common in infants and older children.

Table 23.2

Types of brain tumors in children and their incidence

Tumor type	Incidence
Posterior fossa tumors Medulloblastoma (PNET of cerebellum) Pilocytic (low Grade) astrocytoma Brain stem glioma Ependymoma	55–60% (usually children 3–8 years) 20% 20% 15% 5%
Supratentorial tumors Astrocytoma Glioblastoma	40–55% (usually infants and older children) 15% 10%
Midline
Craniopharyngioma Optic glioma	5% 3%

Tumor type

Incidence

Posterior fossa tumors

Medulloblastoma (PNET of cerebellum)

Pilocytic (low Grade) astrocytoma

Brain stem glioma

Ependymoma

55–60% (usually children 3–8 years)

20%

15%

Supratentorial tumors

Astrocytoma

Glioblastoma

40–55% (usually infants and older children)

15%

10%

Midline

Craniopharyngioma

Optic glioma

PNET primitive neuroectodermal cell tumor

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