Neuroprotection during pediatric cardiac surgery

RAMI .M. WAHBA, M.DLecturer 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