Neuroprotection during pediatric cardiac surgery RAMI .M. WAHBA, M.D Lecturer of Anesthesia and Intensive care Ain Shams University

Introduction Concern towards long-term functional neurological morbidities . this review is foccussing on : adverse neurologic outcomes. factors associated with brain injury. neuroprotection .

Neurologic Outcome early postoperative period (stroke and seizures) longer-term issues (abnormal school performance, learning disabilities,and behavioral issues) cognitive abilities childhood development

Aetiology cerebral injury may occur before, during and after heart surgery. consequences of hypoxic/ischaemic/reperfusion injury may evolve during the postoperative period over several days.

Brain monitoring Real-time neurologic monitoring should be an integral part of neuroprotective strategies . Several monitoring modalities are available.

Electroencephalographic Monitoring signal is affected by electrical interference, patient temperature, anesthetic agents, and CPB. Newer devices use processed EEG technology .

The Bispectral Index (BIS) BIS is used to detect electrical silence during deep hypothermia. BIS values BIS monitoring is reported to detect cerebral hypoperfusion and cerebral air embolism. EEG monitoring is best combined with other neurologic monitoring modalities.

Near infrared spectroscopy (NIRS) A new clinical monitor The NIRS displays a numeric value, the regional cerebral saturation index (rSO2i) rSO2i reflects brain tissue oxygen content influenced by cerebral oxygen delivery, oxygen consumption, and arterial/venous blood volume ratio

Transcranial Doppler Ultrasound sensitive,real-time monitor of cerebral blood flow velocity (CBFV) and emboli . CBF autoregulation is lost at profound hypothermia. Transcranial Doppler ultrasound is used to determine the threshold of detectable cerebral perfusion during low-flow CPB

Multimodality Neurologic Monitoring processed EEG, NIRS, and TCD—measure different aspects of neurologic function . They are complementary rather than exclusive. 90% of abnormal events are detected by NIRS and 10% by TCD (emboli, potential overperfusion of the brain). If resources are limited, NIRS offers the most clinical information to the clinician

Brain Protection Good appreciation of the interplay of factors that influence cerebral metabolism and blood flow is important for brain protection.

Hypothermia and Deep Hypothermic Circulatory Arrest Electrocerebral silence occurs at about 17°C nasopharygeal temperature. deep brain cools faster than the subcortical areas. Current practice is to cool for about 20 minutes to deep hypothermia (15°C to 20°C) .

DHCA causes an immediate cellular energy supply-demand imbalance . the safe period might be 20 to 30 minutes, but this is controversial. Alternatives to DHCA : intermittent cerebral perfusion,regional cerebral perfusion, and low-flow CPB

Intermittant Cerebral Perfusion Cerebral energy metabolism becomes anaerobic with 20 minutes of DHCA. intermittent systemic recirculation during DHCA preventes : -cerebral anaerobic metabolism -improves brain histology and neurologic outcome when compared with DHCA.

Low-flow Cardiopulmonary Bypass low-flow CPB was superior to DHCA with respect to: -High-energy phosphate preservation -Cerebral oxygen metabolism -CBF -Cerebral vascular resistance -Brain lactate levels.

Regional Cerebral Perfusion During aortic arch surgery, DHCA can be avoided by using antegrade cerebral brain perfusion. Continuous regional brain perfusion is achieved at flows of 20 to 30 mL/kg/min.

Hemodilution In the past, hematocrit values have ranged from 10% to 30% when DHCA is utilized Recent data suggest a hemacrit close to 30% might be advantageous.

Acid-base Management on Cardiopulmonary bypass During deep hypothermia, pH-stat management in children : -improves CBF - more effectively cools the brain. -The oxygen dissociation curve shifts rightward, increasing oxygen availability. -There is a more rapid recovery of high-energy phosphates after DHCA. These advantages outweigh the disadvantage of an increase in the embolic load

Compared with a-stat, infants managed with pHstat had lower postoperative morbidity and shorter recovery time to first EEC activity after DHCA. Some advocate that pH-stat should be switched to alpha-stat management when cooling has been achieved.

Glucose Management In 1988 hyperglycemia was reported associated with increased risk of brain injury in children. the Boston Circulatory Arrest Study did not find any relationship between hyperglycemia and neurologic injury in children. avoiding hypoglycemia might be preferable to restricting glucose in infants undergoing heart surgery.

Anti-inflammatory Therapies A study in 29 children undergoing continuous flow CPB found dexamethasone administration before CPB led to a reduction in the post-CPB inflammatory response. Ultrafiltration hemoconcentrates and removes some anti-inflammatory mediators. Leukocyte filtration has improved neurologic outcome after DHCA

Pharmacologic Neuroprotection Agents such as barbiturates, propofol, volatile anesthetics, lidocaine, benzodiazepines, and calcium channel blockers have been shown experimentally to attenuate the neurologic injury from CPB and DHCA. volatile agents,barbiturates, and propofol reduce ischemic neuronal injury after a short postischemic recovery period.

Conclusion Extracorporeal circulation increases the likelihood of neurologic injury, and DHCA represents additional risk. Most children with surgically repaired CHD function within the normal IQ range but do have considerable neurodevelopmental problems.

THANK YOU