Scallan, MJH. (2003). Brain injury in children with congenital heart disease. Pediatric Anaesthesia. 13: 284-93.
Incidence of brain injury
· Incidence of brain injury in children after surgery for congenital heart disease is between 2-25%.
· Various studies show:
o Below expectation IQ scores, expressive language, visual motor integration, motor function, and oro-motor control at 4 years. Problems with attention, learning, and speech at 8 years.
o Increased frequency of developmental delay and cerebral palsy
o If surgery at <1month age - IQ 96 vs 90, CP incidence 25% vs 22%.
o Hypoplastic left heart syndrome worse prognosis (IQ 66, CP incidence 57%)
o Fontan procedure results in lower school performance than general population.
· Risk factors for lower achievement scores:
o Hypoplastic left heart
o Complex procedures
o Circulatory arrest
o Reoperation within 30 days
o Heart transplantation (vs. heart surgery)
· Newer techniques have also seemed to improve neurological outcome.
Etiology of brain injury
· Preoperative causes
o Developmental abnormalities
§ brain dysgenesis
§ genetic mutations, e.g., Down syndrome, 22q11
§ neural crest cells both (i) form cerebral muscular arteries (ii) important in early cardiac development
§ teratogens may affect both brain and heart
o Acquired lesions
§ Hemodynamic disturbances can affect cerebral perfusion
§ Poor brain growth, embolic infarctions, cerebrovascular thrombosis, abscess formation
· Impaired motor function
· Poor attention
· Low academic achievement
· Hypotonia, decreased LOC, convulsions
· Intraoperative causes
o Deep hypothermic circulatory arrest
§ “Safe” period of circulatory arrest is poorly defined – 45 minutes? 20 minutes?
§ Risk of injury increases with duration of circulatory arrest
§ Affects both cognitive and motor development
§ IQ falls by 0.53 points per minute circulatory arrest
o Low flow cardiopulmonary bypass
§ Extended period of suboptimal perfusion
§ Better results than complete circulatory arrest
o Aortopulmonary collaterals
§ Systemic blood that returns to heart without perfusing the systemic vascular bed (3% normal, 30-40% in cyanotic heart disease)
§ Collaterals decrease the rate of cerebral cooling and increase cerebral metabolic derangement
§ Associated with increased risk of choreoathetosis after circulatory arrest
§ Macroemboli or microemboli
§ AAir, fat, clot, platelets, etc.
o Inflammatory causes
§ Microcirculation compromised by vascular and extravascular inflammatory changes after bypass
· Postoperative causes
o Cascade of events occurring days to weeks after surgery due to hypoxia/ischemia/reperfusion injury
o Reperfusion delivers toxic mediators (activated neutrophils) to ischemic tissue
o Immature white matter is particularly vulnerable to free radical attack
o Mitochondrial function impaired after circulatory arrest
o Chronic metabolic derangements up to months after brain ischemia