Pediatric Neuroanesthesia and Critical Care

Neurosurgical lesions in infants and children have distinct manifestations and management issues. Age-related differences in the surgical lesions, anatomy and physiological responses to surgery and anesthesia underlie the clinically relevant differences between pediatric patients and their adult counterparts. Technical advances in neurosurgery and subspecialization in pediatric neurosurgery, anesthesiology and critical care have dramatically improved the outcome in pediatric patients with surgical lesions of the central nervous system (CNS). The perioperative management should be based on the developmental stage of the patient with the caveat that neonates may be vulnerable to iatrogenic CNS injury. The aim of this chapter is to highlight these age- dependent differences and their effects on the management of the pediatric neurosurgical patient during the perioperative period.

Developmental considerations

Differences in cerebrovascular physiology and cranial bone development distinguish infants and children from adults. Cerebral blood flow (CBF) is coupled tightly to metabolic demand, and both increase proportionally immediately after birth. CBF varies with the age of the patient. Computed tomography perfusion scans show that CBF peaks between 2 and 4 years and settles at 7–8 years ( Fig. 20.1 ). These changes mirror those in neuroanatomical development. The idealized autoregulatory range of blood pressure in a normal newborn is between 20 and 60 mmHg, which reflects the relatively low cerebral metabolic requirements and blood pressure during the perinatal period. More importantly, the slope of the autoregulatory curve drops and rises significantly at the lower and upper limits of the curve, respectively ( Fig. 20.2 ).

Cerebral autoregulation is intact in healthy full-term neonates. However, critically ill premature neonates have a linear correlation between CBF and systemic blood pressure. This pattern of CBF pressure-passivity occurs in premature neonates with low gestational age and birth weight, and systemic hypotension. It should be noted that systolic arterial blood pressure is a poor surrogate of cerebral perfusion pressure in premature infants. An assessment of the diastolic blood pressure and CBF velocity may be a better marker of cerebral perfusion pressure in this population. Therefore, tight blood pressure control is essential in the management of neonates to minimize both cerebral ischemia and intraventricular hemorrhage.

Transcranial Doppler studies demonstrated that the lower limit of cerebral autoregulation was equivalent among older and younger children. These observations suggest that children younger than 2 years may have lower autoregulatory reserve because of their relatively low baseline mean arterial pressures and may be at greater risk of cerebral ischemia. Multimodal analysis of cerebral perfusion in infants and children undergoing cardiopulmonary bypass surgery reveal a wide range of lower limits of autoregulation. This observation demonstrates variability in pediatric patients and highlights the limitations of current monitors to optimize cerebral perfusion.

Adults and infants differ in the percentage of cardiac output directed to the brain. CBF is 10–20% of the cardiac output during the first 6 months and peaks at 55% between the second and fourth years. CBF settles to the adult levels of 15% by 7–8 years. The head of the infant and child also accounts for a large percentage of the body surface area and blood volume ( Fig. 20.3 ). This feature places the young child at risk for significant hemodynamic instability during neurosurgical procedures.