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25. Neurophysiology

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Title: 25. Neurophysiology


1
25. Neurophysiology Anesthesia
  • R1 ???

2
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    

3
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?
    ?? ??

4
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? ??? ???
    ??

5
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? ???? ?? 

6
CEREBRAL PHYSIOLOGY
  •   
  • CEREBROSPINAL FLUID
  • CNS ? trauma??? ??
  •     ???? ? 21mL/h ????
  • ??? ?150ml????

7
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

8
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 ??? ??
  •                 
  •   
  •      

9
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??

10
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
  •                

11
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
  •                  

12
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 ??
  •                  

13
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 ?? ?? ? ? ??
  •                  

14
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?? ??

15
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? ?? ???? ???

16
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 ??

  
17
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?
  • ???? ???? ??? ??

18
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

19
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?
    ???? ? ? ??
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