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

§         Results:

·         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

o        Emboli

§         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