monitoring during neurosurgery by dr. mai mohsen abdel aziz lecturer of anesthesia, ain shams...
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Monitoring during Monitoring during neurosurgeryneurosurgery
Monitoring during Monitoring during neurosurgeryneurosurgery
ByByDr. Mai Mohsen Abdel AzizDr. Mai Mohsen Abdel Aziz
Lecturer of anesthesia , Ain Shams UniversityLecturer of anesthesia , Ain Shams University
The CNS can sometimes be insufficiently monitored leading to grave postoperative complications
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
What do we want to monitor?
A. Monitor of brain electrical activity
1. Electroencephalography2. Evoked potentials: I. Sensory evoked
potentials . Visual
. Somatosensory
. Auditory II. Motor evoked
potentials 3. Bispectral index
B. Monitor of intracranial pressure and blood flow dynamics:
1. Intracranial pressure monitoring2. Jugular venous oximetry3. Transcranial doppler sonography4. Brain tissue oxygen tension monitor5. Near-infrared spectroscopy
1. Electroencephalography
Value:1.Measures electrical function of brain 2.Indirectly measures blood flow3.Measures anesthetic effects4.Guide reduction of cerebral metabolism prior to
induced reduction of blood flow5.Predict neurologic outcome after brain insult
6.During cortical mapping in surgery for epilepsy . 6.During cortical mapping in surgery for epilepsy .
7. In cardiac surgery : to determine the end point 7. In cardiac surgery : to determine the end point for hypothermia during circulatory arrest by EEG for hypothermia during circulatory arrest by EEG isoelectricity ( EEG burst suppression).isoelectricity ( EEG burst suppression).
• 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
Abnormal EEG detect
Regional Global . Epilepsy . Global ischemia
. Focal ischemia . Hypoxemia
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
•Anesthetic drugs affect frequency and
amplitude of EEG waveformseg.barbiturates produce initial activation, then dose-related depression while ketamine activates EEG at low doses and cannot achieve electrocortical silence.
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
• 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
2. Evoked potentialsI. 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%
When do we use it?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
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…
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..
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
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)
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
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
Is it sensitive?• More sensitive in detecting post-operative
motor deficits• Intravenous agents produce significantly less
depression• Muscle relaxants interfere
3. Bispectral index 3. Bispectral index (BIS)(BIS)
• integrates single-channel EEG integrates single-channel EEG • The BIS value of The BIS value of 100 100 indicate the patient is indicate the patient is
fully awake.fully awake.The BIS value of The BIS value of 00 indicated absence of brain indicated absence of brain activity.activity.
• used to monitor depth of anesthesia (with a used to monitor depth of anesthesia (with a
target of less than target of less than 6060) )
Value?• reduce the overall anesthetic dose and its reduce the overall anesthetic dose and its
related side effectsrelated side effects• Decreases the incidence of postoperative Decreases the incidence of postoperative
awarenessawareness• shorten emergence time shorten emergence time • and allow early postoperative recoveryand allow early postoperative recovery
Monitors of blood flow Monitors of blood flow dynamicsdynamics
1.Transcranial doppler1.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
When is it used?• evaluate integrity of cerebral vasculature in evaluate integrity of cerebral vasculature in
carotid endarterectomy surgery.carotid endarterectomy surgery.• In cardiac surgery: can be used as a tool to In cardiac surgery: can be used as a tool to
detect and quantify embolic phenomena in detect and quantify embolic phenomena in MCA. MCA.
• Detection of vasospasm
2. Cerebral Oximetry (Near infrared spectroscopy)
• determine cerebral saturation • uses a similar principle to pulse oximetryuses a similar principle to pulse oximetry
bby using multiple wave lengths of near y using multiple wave lengths of near infrared lightinfrared light , , the absorption of this light by the absorption of this light by oxygenated and deoxygenated haemoglobinoxygenated and deoxygenated haemoglobin determines determines
the overall saturation the overall saturation of the blood present withinof the blood present within
the brain tissues.the brain tissues.
Is it sensitive?– High intersubject variability– Low specificity
When is it used ?– cardiac surgery to detect the cerebral cardiac surgery to detect the cerebral
desaturation (20% from the base cerebral desaturation (20% from the base cerebral saturation) with CPB .saturation) with CPB .
– carotid endarterectomycarotid endarterectomy
3. Jugular venous oxygen saturation (SjVO2)
The jugular bulb is the dilated portion of the The jugular bulb is the dilated portion of the jugular vein just below the base of the skull jugular vein just below the base of the skull which contain blood with little extra cerebral which contain blood with little extra cerebral contamination. contamination.
Measurement of oxygen saturation of the jugular Measurement of oxygen saturation of the jugular bulb provide information about the global bulb provide information about the global oxygenation state of the brain.oxygenation state of the brain.
• Analysis of the bulb saturation can be performed Analysis of the bulb saturation can be performed by:by: -Intermittent blood sampling via standard -Intermittent blood sampling via standard intravascular catheters. intravascular catheters. -Continuous fiberoptic jugular probes placed -Continuous fiberoptic jugular probes placed retrograde via the internal jugular vein in the retrograde via the internal jugular vein in the jugular bulb. jugular bulb.
• Was primarily employed in cardiac surgery: SjvO2 Was primarily employed in cardiac surgery: SjvO2 was used to study the cerebral desaturation with was used to study the cerebral desaturation with the CPB the CPB
• relatively invasive and insensitive technique. relatively invasive and insensitive technique. • has been replaced by noninvasive cerebral has been replaced by noninvasive cerebral
oximetery.oximetery.
4.Direct tissue oxygen 4.Direct tissue oxygen monitoringmonitoring
• Direct measurement of brain O2 level (PO2) Direct measurement of brain O2 level (PO2) with small oxygen electrodes placed through a with small oxygen electrodes placed through a burrhole.burrhole.
• It is used mainly in traumatic brain injury (TBI) It is used mainly in traumatic brain injury (TBI) to prevent secondary cerebral ischemia .to prevent secondary cerebral ischemia .
• decrease in direct brain PO2 less than 20 decrease in direct brain PO2 less than 20 mmHg should be treated by improving oxygen mmHg should be treated by improving oxygen delivery delivery
-ICP <20mmHg-ICP <20mmHg
-CPP >60mmHg, -CPP >60mmHg,
-increasing FiO2, hemoglobin and decreasing -increasing FiO2, hemoglobin and decreasing oxygen demand with sedationoxygen demand with sedation
Conclusion Multimodality in monitoring the brain is Multimodality in monitoring the brain is
important as no single monitor provides important as no single monitor provides definite information regarding brain definite information regarding brain function.function.
However integrating the information However integrating the information from several monitors may provide a from several monitors may provide a therapeutic guide for intervention and therapeutic guide for intervention and reducing morbidity and mortality. reducing morbidity and mortality.
If we care, we can
Thank You