25. Neurophysiology

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25. Neurophysiology Anesthesia

• R1 ???

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CEREBRAL PHYSIOLOGY

• CEREBRAL METABOLISM
• ?? total body oygen? 20? ????
• ?? 60? ATP? ????? ????
• NEURONAL ELECTRICAL activity
• hippocampus? cerebellum? ?? ??
• irreversible cellular injury?????
• cerebral perfusion 10?
• blood flow 3-8?
• primary energy source  glucose
• hypoglycemia hypoxia?? ??
• hyperglycemia cerebral acidosis cellular
  injury
• --gt global focal
  hypoxic injury    

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CEREBRAL PHYSIOLOGY

• CEREBRAL BLOOD FLOW
• CBF ? metabolic activity ? ??? flow??? cerebral
  metabolic rate?????
•   
• REGULATION OF CEREBRAL BLOOD FLOW (1)
•   1.Cerebral Perfusion Pressure(CPP)
•      CPP MAP ICP (or CVP)
•       ?, CVP? ICP?? ??? ?? ? CVP??
•      CPP? 80-100mmHg
•      ?? ICP? 10mmHg?? ??
•      ???? CCP? MAP?? ????
•       
•   2.Autoregulation
•      ???? ???????? ??? ? ???? blood flow? ? ???
  ??
•      ?? ?? CPP? ?? ?? cerebral vasodilation? ???
  ??
•      CBF ? MAP 60160mmHg????? ?????
•      ???? ?? flow? pressure ? ??? ??
•      BBB? disrupt??? cerebral edema?? hemorrhage?
  ?? ??

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CEREBRAL PHYSIOLOGY

• REGULATION OF CEREBRAL BLOOD FLOW (2)
• 3.Extrinsic Mechanism
•    Respiratory Gas Tensions
•       ?? PaCO2??, CBF ??? ??? ?? ? ???
•       20-80mmHg????, CBF? PaCO2? ??
•       ????? CSF ? ?  ??? pH? ??? ???
•        
•     Temperature
•        CBF ? ??1?? ??? ?? 5-7? ???
•        Hypothermia CMR? CBF? ??
•        
•     Viscosity
•         viscosity? ????? hematocrit ??
•         ????? CBF ? ? ??? ??
• Autonomic influences
•         brain injury? stroke? vasospasm? ??? ???
  ??

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CEREBRAL PHYSIOLOGY

•    BLOOD-BRAIN BARRIER
• ?? ???? vascular endothelial cell???
  junction??
•   
•  lipid barrier?? lipid soluble substances?
  ?????
•    ionized??large molecular weight ? ?? ??? ????
•    ? ??,charge,lipid solubility,??? protein
  binding? ??? ????
•   
•   CO2, O2, lipid soluble substances(???? ????)?
  ?????
•  
•   water freely across
•  
•   electrolyte? osmolality??? ????, sodium??
  glucose?? ??? ????  
•   mannitol?? BBB?? ??? water content? ???? ?? 

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CEREBRAL PHYSIOLOGY

•   
• CEREBROSPINAL FLUID
• CNS ? trauma??? ??
•     ???? ? 21mL/h ????
• ??? ?150ml????

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CEREBRAL PHYSIOLOGY

•    INTRACRANIAL PRESSURE
• Cranial vault? rigid structure?? brain(80),
  blood(12), CSF(8)? ??
•    ???? ???? ????? ???? ??? ?? ICP ? ????
•    ICP? ??? supratentorial CSF pressure? ???
• lateral ventricle?? cerebral cortex??
  ???? ?? 10mmHg??
•      ??? lumbar CSF pressure? ????? ??
•    major compensatory mechanism
•      (1) initial displacement of CSF (from
  cranial to spinal compartment)
•      (2) CSF ? ?? ??
•      (3) CSF ?? ??
•      (4) total cerebral blood volume? ??
•    ??? compliance? arterial blood pressure?  
• PaCO2? ??? ??
  ?????
•      blood pressure? ???
  vasoconstriction, vasodilation

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INHALATION AGENTS (1)
• 1.Volatile Anesthetics
•    Cerebral Metabolic Rate
•      dose-dependent ?? ??
•      Isoflurane? ?? ??(50?? ??)
•         
•    Cerebral Blood Flow Volume
•      cerebral blood vessels? dilatation,
  autoregulation? impair by dose-dependent
•      halothane CBF ? ?? ? ?? (200?? ??)
•                   cf.Isoflurane? 20??
•      time-dependent 2-5???? ????? ???
• blood flow? ????
  ???? ????
•      hyperventilation (hypocapnia) ? ?????? CBF ?
  ??????
•        
             ????? ??? ???? -gtICP ??? ??
•                 
•   
•      

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INHALATION AGENTS (2)
• Cerebrospinal Fluid Dynamics
•         CSF? ??? ??? ??
•         Isoflurane ??? ??
•  Intracranial Pressure
•        ?????? ????? CBF ? ?????
•        ??? CSF dynamics, arterial CO2 tension?
  ?????
•         choice - isofluane
• 2.Nitrous Oxide
•      intravenous agent? ??? minimal effect on
  CBF, ?, and ICP
•       ?? ??? ICP??

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INTRAVENOUS AGENTS (1)
• 1.Induction Agents (1)
•     Ketamine? ????? ?? ?????? CMR, CBF? ?? ???
  ???
•          ??? ?????
•     cerebral autoregulation? CO2???? ????
•     ???, blood flow? metabolic rate? parallel??
•      
•    Barbiturates
•       CNS ? 4?? ??
•          (1) hypnosis
•          (2) CMR? ??
•          (3) CBF ? ????? cerebral vascular
  resistance? ??
•          (4) anticonvulsant activity
•       CMR, CBF? ??? EEG? isoelectric????
  dose-dependent (?? 50??)
•       barbiturate-induced vasoconstriction
• -gtnormal? ????
  ishemia? ???? ??????
•       CSF? ??? ?? -gt lower ICP
•                

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INTRAVENOUS AGENTS (2)
• 1.Induction Agents (2)
• Opioids
•       CBF , CMR ,ICP? ????? ??????
•       ??????? CO2? ????
•  Etomidate
•       CMR CBF ICP ??
•        induction ? myoclonic movement ?? ???
  ??????
•        (?? seizure?? ????)
•        epilepsy Hx?????? avoid
•   Propofol
•        CBF CMR ??
•        Anticonvulant activity? ??
•        short elimination half-life
•                  

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INTRAVENOUS AGENTS (3)
• 1.Induction Agents (3)
• Benzodiazepines
•        barbiturates, etomidate, and propofol ???
  ????,
• CBF CMR ? ??
•        anticonvulsant properties
•        midazolam? short half-life??? choice???
•        ?? ???? unstable ???? CPP? ????
• 
  emergence? ????              
•      Ketamine
•        cerebral vasculature? ????? CBF ? ?????
•        seizure activity? ???
•        Intracranial compliance? ????? ??? ???
• CBF ????? ICP ??
•                  

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EFFECT OF ANESTHETIC AGENTS ON CEREBRAL PHYSIOLOGY

• EFFECT OF INTRAVENOUS AGENTS (4)
• 2.Anesthetic Adjuncts
•       Iv lidocaine ??????? ??? CMR CBF ICP??
•      systolic toxicity?
  seizures ???? ?? repeat dose??
•  3.Vadopressors
•      MAP? 50-60mmHg?? ?? 150-160mmHg??? ?? CBF ??
  
•      
•  4.Vasoilators
•      Hypotension? ?? ??, ???? vasodilators?
  cerebral vasodilation?
•       ???? CBF ? dose-relate?? ?? ???
•       
•  5.Neuromuscular Blocking Agents
•      succinylcholine - ?? ??
•      (thiopental or propofol? ???,
  hyperventilation?? ??? ??)
•      ICP? ??? ?? ??? ???????
•      hypercapnia?? hypoxemia? acute ?? ?? ? ? ??
•                  

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PHYSIOLOGY OF BRAIN PROTECTION

• PATHOPHYSIOLOGY OF CEREBRAL ISCHEMIA
•  ?? ?? ??? glucose metabolism??? ischemic injury?
  ????
• ex. interruption of cerebral perfusion,
  metabolic substrate, or hypoxemia
• STRATEGIES  FOR BRAIN PROTECTION (1)
•   1.Hypothermia
•      focal and global ischemia? most effective
  method
•      profound hypothermia? ?? total circulatory
  arrest???
•       neurologic impairment?? 1???? ????
•      basal and electrical metabolic requirements?
  ?????
•      mild hypothermia(33-35?) - some protective
  effect? ???
•      
  adverse effect? profound hypothermia?? ??

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PHYSIOLOGY OF BRAIN PROTECTION

• STRATEGIES  FOR BRAIN PROTECTION (2)
•   2. Anesthetic Agents
•      barbiturates,etomidate,propofol, and
  isoflurane
•        - complete electrical silence of the
  brain
•          eliminate the metabolic cost of
  electrical activity
•      barbiturates produce inverse steal
•                    reduce cerebral edema and
  calcium influx
•                   inhibit free radical
  formation
•                    blockade of sodium
  channels
•            -- effective brain
  protection in focal ischemia
•      anesthetic agents? global ischemia?? ??? ??
  (only hypothermia)
•  
• 3. Specific Adjuncts
•      calcium channel blockers
•         cerebral vasodilation but CBF ??
•         neurologic outcome? ?? ???? ???

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PHYSIOLOGY OF BRAIN PROTECTION

• STRATEGIES  FOR BRAIN PROTECTION (3)
•  4.General Measures
•     ??? CPP??? ????
•        1) arterial blood pressure normal or
  slight elevated
•        2) avoid - venous and ICP ??
•        3) oxygen carrying capacity
• normal arterial tension
  hematocrit 30
•  
•  Hyperglycemia neurologic injury ??
•     normocarbia?? hypo? cerebral
  vasoconstriction -gt ischemia ??
•                        hyper? steal
  phenomena ?? acidosis ??

  
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PHYSIOLOGY OF BRAIN PROTECTION

• EFFECT OF ANESTHESIA
• ON ELECTROPHYSIOLOGICAL MONITORING
• CNS ? ??? ??
• ?? EEG ?? Evoked potentials??
• anesthetic depth- dose- related change
•   blood pressure, body temperature,
• respiratorygas tension? ????
•    recording? bilateral,??? event?
• ???? ???? ??? ??

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PHYSIOLOGY OF BRAIN PROTECTION

• ELECTROENCEPHALOGRAPHY (1)
• EEG cerebral perfusion? ??
•   carotid endarterectomy(CEA), controlled
  hypotension ? ??
•   ???? ?????? biphasic pattern? ????
•     dose-dependent depression ? ?? initial
  activation? EEG?? ???? 
•   
• 1.Inhalation Anesthetics
•     Isoflurane high dose(1-2 MAC)???
  isoelectric EEG? ???? ??? ??
•     Sevo and Des burst suppression pattern at
  high dose
•  2.Intravenous Agents
•     Benzodiazepines typicalbiphasic pattern on
  EEG
•     Barbiturates, etomidate, and propofol
  typical biphasic pattern
•                            high dose??? burst
  suppression and electrical silence

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PHYSIOLOGY OF BRAIN PROTECTION

• EVOKED POTENTIALS
•     somatosensory evoked potentials(SSEPs)
•         dorsal spinal columns? sensory cortex?
  ??? ??
•          spinal tumor? resection and spine, CEA,
  aortic surgery? ???
• ? ????
•     
•  brain stem auditory evoked potentials
•           8th nerve and auditory pathway above
  pons
•    
•   visual evoked potentials optic nerve and
  upper brain stem  
•   
•    EEG ?? more complicated??
•       ??? ?? short and intermediate potentials?
  ???? ? ? ??