Transcript neuroprotection in pediatric cardiac surgery

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 .
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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.
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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 lowflow 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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