neuroprotection during pediatric cardiac surgery
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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. - PowerPoint PPT PresentationTRANSCRIPT
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.
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