SUMMARY: - Neurophysiologic monitoring not universally adopted but in many centers has become routine monitor for some surgical procedures - Ideal neurophysiologic monitoring in the neurosurgical procedure should be: non-invasive (v.s invasive), high sensitivity & specificity, cost effective, easy to use, simple instrumentation, and real time or continous monitoring.

1. Pertemuan Ilmiah Berkala PERDATIN 2014
Grand Clarion Hotel and Convention-Makassar
Syafruddin Gaus
Dept. of Anesthesiology, Intensive Care, and Pain Management
Faculty of Medicine, Hasanuddin University

2. Introduction
 Patients with neurologic disease undergoing
surgical procedures have increased risk of
ischemic / hypoxic damage to the CNS
 Risk may be related to hemodynamic /
embolic events associated with:
* non-neurosurgical operation (CPB)
* neurosurgical procedure (temporary
clipping during cerebral aneurysm surgery

3. Introduction
 Intraoperative neurophysiologic monitoring
may improve patient outcome by:
 allowing early diagnosis of ischemia/hypoxia
before irreversible damage occurs
 enabling surgeons to provide optimal operative
treatment as indicated by the monitoring
parameter.

4. Introduction
 The brain can be monitored in terms of:
 function
 cerebral blood flow (CBF) & intracranial
pressure (ICP)
 brain oxygenation and metabolism

5. Monitoring of Function
 Electroencephalograms (EEG)
 Raw EEG
 Computerized Processed EEG: Compressed
spectral array, Density spectral array, Aperiodic
analysis, Bispectral analysis (BIS)
 Evoked Potential
 Sensory EP:
○ Somatosensory EP
○ Visual EP
○ Brain stem auditory EP
 Motor EP:
- Transcranial magnetic MEP
- Transcranial electric MEP
- Direct spinal cord stimulation
 EMG
- Cranial nerve function (V, VII, IX, X, XI, XII)

6. EEG
 Result of excitatory postsynaptic potential
 EEG Waves :
 Beta: high freq, low amp (awake state)
 Alpha: med freq, high amp (eyes closed while
awake)
 Theta: Low freq (not predominant)
 Delta: very low freq hugh amp (depressed
functions/deep coma)
 EEG waves reflects state of arousal and
metabolism depends on energy
substrates supply  blood flow

7. EEG
 Sudden development of delta waves
coincident with surgical manuver 
injury warning
 In penumbra region, EEG poorly predict
brain damage
 Anesthetics & hypothermia causes EEG
changes  multifactorial interpretation

8. EEG
 Indication:
 Surgery that place the brain at risk
(difficulties: restricted access)
 Anesthesia induced metabolic suppresion
 Seizure monitoring in ICU

9. Indication for EEG
Monitoring  Carotid endarterectomy
 Cerebral aneurysm surgery when
temporary clipping is used.
 Cardiopulmonary bypass
procedure
 Extracranial-intracranial bypass
procedure
 Deliberate metabolic supression
for cerebral protection.
Newfield P, Cottrell JE. Handbook of
Neuroanesthesia;2012

10. Bispectral Index
 Bispectral analysis (BIS)
 Monitor degree of hypnosis (40-60 
adequate hypnosis)
 Doesn’t detect ischemia

11. Evoked Potential Monitoring
 Sensory Evoked Potential (SEP)
 Time-locked, event related, pathway specific
EEG in respones of peripheral stimulus
 Resistant to IV anesthetics, recordable in
inhalation anesthetics (dose related)
 Monitor integrity of the pathway from
periphery to the cortex

12. Evoked Potential Monitoring
• Somatosensory Evoked Potential (SSEP)
○ Electrical stimulator placed at median, ulnar, or
posterior tibial nerves.
○ Used in spinal column surgery to asses potential
risk to the spinal cord
• Visual Evoked Potential (VEP)
○ Using LED goggles to create stimulus
○ Difficult to perform
• Brainstem Auditory Evoked Potential (BAEP)
○ Repetitive clicks delivered to the ear
○ Reflects the VIII nerve & brainstem “well-being”

13. Indication for SEP Monitoring
SSEP Monitoring:
 Spinal column surgery
 Carotid endarterectomy
 Cerebral aneurysm
surgery
BAEP Monitoring:
 Acoustic neurinoma
 Vertebral-basilar
aneurysm
 Other posterior fossa
procedure.
SSEP: somatosensory evoked potential
BAEP: brain stem auditory evoked potential

14. Evoked Potential Monitoring
 Motor Evoked Potential (MEP)
 Monitors motoric pathway  as a
complement of SSEP
 Basically an electromyographic using train
of four stimuli
 Instant feedback
 Can’t be recorded if muscle relaxant used

15. Monitoring of CBF and ICP
 Absolute CBF.
 Nitrous oxide wash in (jugular bulb
cannulation) invasive
 Xenon clearance non invasive
 Relative CBF
 Laser Doppler Flowmeter (LDF) measure
flow quantitatively (1 mm brain tissue).
 Requires a burr hole.

16. Monitoring of CBF and ICP
 Transcranial Doppler (TCD) –overview-
 Measure CBF velocity in the Circle of Willis
noninvasively and continuously
 Intraoperative middle cerebral artery
measured by placing probe over zygomatic
arch
 Qualitative assesment tools for ICP
 Detects air / particulate emboli

17. Monitoring of CBF and ICP
 Transcranial Doppler (TCD) –principles-
 Flow can be measured if the vessel diameter
remain constant Basal Cerebral Arteries
 The diameter remain constant as the vascular
resistance changes or during administration of
IV or inhaled anesthetics
 The diameter only constricts during vasospasm
in subarachnoid hemorhage
 Once confirmed by angiography, TCD can track
patient’s response to therapy of the vasospasm
 Changes in flow velocity correlates with CBF

18. Monitoring of CBF and ICP
 Transcranial Doppler (TCD) –clinical app-
 Carotid endarterectomy:
○ Detection of ischemia if 60% Vmca decrease from
baseline
○ Detection of microemboli
○ Diagnosis of postoperative hyperperfusion syndrome
○ Diagnosis of postoperative intimal flap or thrombosis
 Cardiac Surgery (cognitive dysfunction 30-70%):
○ Cerebral emboli during cardiopulmonary bypass
○ Cerebrl perfusion during cardiopulmonary bypass
 Closed Head Injury:
○ Assess autoregulation, diagnose hyperemia,
vasospasm, and intracranial circulatory arrest
Diagnosis of brain death

19. Monitoring of CBF and ICP
 ICP monitoring:
 Optimizes Cerebral Perfusion Pressure
(CPP)
 Prevents possible herniation
 Methods: ventriculostomy, subarachnoid
bolt, epidural sensor, fiberoptic
intraparenchymal monitor (commonly used)
 Can be incorporated with LDF, brain
temperature, PaO2, PaCO2, and pH
monitoring

20. Monitoring of Cerebral
Oxygenation and Metabolism
 Invasive monitoring:
 Brain tissue oxygenation
 Jugular bulb venous oximetry monitoring
 Microdialysis catheter
 Non-Invasive monitoring:
 Near Infrared Spectroscopy (NIRS)

21. Monitoring of Cerebral
Oxygenation and Metabolism
 Brain tissue oxygenation (Po2)
 Po2 monitor is useful to assess O2 demand and
supply
 The tissue Po2 monitor is placed intraparenchymal-ly
in conjunction with ICP monitor.
 Reveals regional or local O2 levels
 O2 tension 10 mmHg: threshold for brain hypoxia

22. Monitoring of Cerebral
Oxygenation and Metabolism
 Brain tissue oxygenation (Po2)
 Po2 : increasing supply O2 (supplemental O2,
raising CPP, treating anemia)
 Po2 : decreasing demand (propofol or barbiturate
therapy)
 Loss of cerebral autoregulation: may demonstrate
hyperoxia that could occur with cerebral hyperemia
 Monitor placement ? Normal brain parenchyma or
adjacent to the injured brain

23. Monitoring of Cerebral
Oxygenation and Metabolism
 Jugular bulb venous oximetry monitoring
 Provide GLOBAL cerebral oxygen
demand and supply
 Relative CBF estimated by calculation of
arteriovenous oxygen content
difference reflects oxygen balance
 Intraoperative cerebral ischemia can be
diagnosed readily
 Limitation: unable to detect focal
ischemia

24. Monitoring of Cerebral
Oxygenation and Metabolism
 Interpretation of jugular venous oxygen
saturation (SjvO2)
 Increased values: >90% indicates absolute/relative
hyperemia
○ Reduced metabolic need  comatose/brain death
○ Excessive flove  sever hypercapnia
○ AVM
 Normal Values: 60-70%  focal ischemia?
 Decreased Values: <50%  increased O2 extraction,
indicates a potential risk of ischemia injury
○ Increased demand: seizure / fever
○ Decreased supply: decreased flow, decreased hematocrit
 As ischemiaprogress to infarction: O2
consumption decreases

25. Monitoring of Cerebral
Oxygenation and Metabolism
 Microdialysis catheters
 Small catheter inserted with ICP/tissue PO2
monitor
 Artificial cerebrospinal fluidequilibrates with
extracellular fluid chemical composition
analysis
 Markers:
○ Lactate/pyruvate ratio  onset of ischemia
○ High level glycerol inadequate energy to
maintain cellular integrity membrane
breakdown
○ Glutamate neuronal injury and a factor in its
exacerbation
 Catheter placement is important small
coverage

26. Monitoring of Cerebral
Oxygenation and Metabolism
 Near-infrared Spectroscopy (NIRS)
 Transcranial oximetry
 Measure cerebral regional O2 reflected
by the chromophobes in the brain
 Limits:
○ Intersubject variability
○ Potential contamination from
extracranial blood
○ Lack definable threshold
 Might be promising in neonate & infant
due to thin skull & scalp

27. Summary
 Neurophysiologic monitoring not universally
adopted but in many centers has become
routine monitor for some surgical procedures
 Ideal neurophysiologic monitoring in the
neurosurgical procedure should be: non-invasive
(v.s invasive), high sensitivity &
specificity, cost effective, easy to use, simple
instrumentation, and real time or continous
monitoring.