1. Monitoring during neurosurgeryBy
Dr. Mai Mohsen Abdel Aziz
Lecturer of anesthesia , Ain Shams University

2. The CNS can sometimes be insufficiently monitored leading to grave postoperative complications

3. Why do we need it ?
Monitor functional integrity of neural structures (nerves, spinal cord, certain brain areas)
Reduce the risk of iatrogenic damage to the nervous system
Provide functional guidance to the surgeon and anesthiologist
Locate neural structures (eg. Locate cranial n. during skull base surgery)
Reduce morbidity and mortality without introducing additional risks

4. What do we want to monitor?
A. Monitor of brain electrical activity
Electroencephalography
Evoked potentials:
I. Sensory evoked potentials
. Visual
. Somatosensory
. Auditory
II. Motor evoked potentials
3. Bispectral index

5. B. Monitor of intracranial pressure and blood flow dynamics:
Intracranial pressure monitoring
Jugular venous oximetry
Transcranial doppler sonography
Brain tissue oxygen tension monitor
Near-infrared spectroscopy

6. 1. Electroencephalography
Value:
1.Measures electrical function of brain
2.Indirectly measures blood flow
3.Measures anesthetic effects
4.Guide reduction of cerebral metabolism prior to induced reduction of blood flow
5.Predict neurologic outcome after brain insult
6.During cortical mapping in surgery for epilepsy .
7. In cardiac surgery : to determine the end point for hypothermia during circulatory arrest by EEG isoelectricity ( EEG burst suppression).

7. 3 parameters of the signal:
Amplitude – size or voltage of signal
Frequency – number of times signal oscillates
Time – duration of the sampling of the signal

8. . Epilepsy . Global ischemia
Abnormal EEG detect
Regional Global
. Epilepsy Global ischemia
. Focal ischemia . Hypoxemia

9. Anesthetic Agents and EEG
Light anesthesia : Larger voltage, slower frequency
General anesthesia : Irregular slow activity
Deeper anesthesia : Alternating activity
Very deep anesthesia : Burst suppression  eventually isoelectric

10. Anesthetic drugs affect frequency and amplitude of EEG waveforms eg
Anesthetic drugs affect frequency and amplitude of EEG waveforms eg.barbiturates produce initial activation, then dose-related depression while ketamine activates EEG at low doses and cannot achieve electrocortical silence.

11. Non-anesthetic Factors Affecting EEG
Surgical
Cardiopulmonary bypass
Occlusion of major cerebral vessel (carotid cross-clamping, aneurysm clipping)
Retraction on cerebral cortex
Surgically induced emboli to brain
Pathophysiologic Factors
Hypoxemia
Hypotension
Hypothermia
Hypercarbia and hypocarbia

12. What to do if EEG technician indicates a possible problem?
Check to see if anesthetic milieu is stable
Rule out hypoxemia, hypotension, hypothermia, hypercarbia and hypocarbia
Raise the MAP, obtain ABG
See if there is a surgical reason

13. 2. Evoked potentials I. Somatosensory evoked potentials (SSEP)
What does it monitor?
Monitor dorsal column-medial lemniscus pathway to assess spinal cord function
Stimulus is applied to a nerve distal to surgical site and recording is made from the cerebral cortex or other locations rostral to surgery
Baseline is obtained, significant changes amplitude >50%
Latency >10%

14. When do we use it? Is it specific? The response is non-specific.
spinal surgery…
deliberate hypotension…
Thoracic aortic aneurysm…
Carotid endarterectomy…
Cerebral aneurysm…
Is it specific?
The response is non-specific.
Can be affected by hypoperfusion,
temperature changes, changes in anesthetic drugs

15. II. Visual evoked potential (VEP)
Visual stimuli from flashing diodes in goggles measures intactness of visual pathways from optic nerve to occipital cortex
Very sensitive to anesthetic drugs and variable signals
When can we use it?
Trans-sphenoidal …
anterior fossa surgeries…

16. III. Auditory evoked potentials (AEP)
Auditory signal transmitted to patient follows auditory pathways CN VIII, cochlear nucleus, rostral brain stem, inferior colliculus, auditory cortex
It is resistant to anesthetic drugs
When do we use it?
Decompression of CN VIII…
Resection of acoustic neuroma..

17. Anesthetic Agents and SEPs
Most anesthetic drugs increase latency and decrease amplitude
Volatile agents: increase latency, decrease amplitude
Barbituates: increase in latency, decrease amplitude
Exceptions:
Nitrous oxide: latency stable, decrease amplitude
Etomidate: increases latency, increase in amplitude
Ketamine: increases amplitude
Opiods: no clinically significant changes
Muscle relaxants: no changes

18. Physiologic Factors and SEP’s
Hypotension
Hyperthermia and hypothermia
Hypoxemia
Hypercapnea
Significant anemia (HCT <15%)
Technical factor: poor electode-to skin-contact and high electrical impedence (eg electrocautery)

19. How do we manage?
. First rule out systemic factors:
improve neural tissue blood flow and nutrient delivery
Intravascular volume and cardiac performance optimized (crystalloid/colloid or blood) to increase oxygen-carrying capacity – optimal HCT 30% or higher
Elevate MAP
Blood gas – assure oxygenation, normocarbia to help improve collateral blood supply if hypocarbic
Consider steroids (shown to work with traumatic spinal cord injury)
Mannitol – improve microcirculatory flow and reducing interstitial cord edema
. Second rule out neurological factors: ischemia or nerve compression

20. IV. Motor evoked potentials
Spinal cord monitoring esp. motor tracts not covered by SSEP monitoring
Substituted old-fashioned Stagnara wake-up test
It is the reverse of SSEP, motor cortex is stimulated transcranially
Recordings are made from muscles in the limb or from spinal cord caudal to surgical site
When can we use it?
Spine surgeries

21. Is it sensitive?
More sensitive in detecting post-operative motor deficits
Intravenous agents produce significantly less depression
Muscle relaxants interfere

22. 3. Bispectral index (BIS)
integrates single-channel EEG
The BIS value of 100 indicate the patient is fully awake. The BIS value of 0 indicated absence of brain activity.
used to monitor depth of anesthesia (with a target of less than 60)

23. Value? reduce the overall anesthetic dose and its related side effects
Decreases the incidence of postoperative awareness
shorten emergence time
and allow early postoperative recovery

24. Monitors of blood flow dynamics 1.Transcranial doppler
Direct, noninvasive measurement of CBF
Sound waves transmitted through
thin temporal bone contact blood,
are reflected, and detected
Most easily monitor middle
cerebral artery

25. When is it used?
evaluate integrity of cerebral vasculature in carotid endarterectomy surgery.
In cardiac surgery: can be used as a tool to detect and quantify embolic phenomena in MCA.
Detection of vasospasm

26. 2. Cerebral Oximetry (Near infrared spectroscopy)
determine cerebral saturation
uses a similar principle to pulse oximetry by using multiple wave lengths of near infrared light , the absorption of this light by oxygenated and deoxygenated haemoglobin determines
the overall saturation
of the blood present within
the brain tissues.

27. Is it sensitive? When is it used ? High intersubject variability
Low specificity
When is it used ?
cardiac surgery to detect the cerebral desaturation (20% from the base cerebral saturation) with CPB .
carotid endarterectomy

28. 3. Jugular venous oxygen saturation (SjVO2)
The jugular bulb is the dilated portion of the jugular vein just below the base of the skull which contain blood with little extra cerebral contamination.
Measurement of oxygen saturation of the jugular bulb provide information about the global oxygenation state of the brain.

29. Analysis of the bulb saturation can be performed by: Intermittent blood sampling via standard intravascular catheters Continuous fiberoptic jugular probes placed retrograde via the internal jugular vein in the jugular bulb.
Was primarily employed in cardiac surgery: SjvO2 was used to study the cerebral desaturation with the CPB
relatively invasive and insensitive technique.
has been replaced by noninvasive cerebral oximetery.

30. 4.Direct tissue oxygen monitoring
Direct measurement of brain O2 level (PO2) with small oxygen electrodes placed through a burrhole.
It is used mainly in traumatic brain injury (TBI) to prevent secondary cerebral ischemia .

31. decrease in direct brain PO2 less than 20 mmHg should be treated by improving oxygen delivery
-ICP <20mmHg
-CPP >60mmHg,
-increasing FiO2, hemoglobin and decreasing oxygen demand with sedation

32. Conclusion
Multimodality in monitoring the brain is important as no single monitor provides definite information regarding brain function. However integrating the information from several monitors may provide a therapeutic guide for intervention and reducing morbidity and mortality.

33. If we care, we can
Thank You