Presentation on theme: "Monitoring during neurosurgery"— Presentation transcript:
1Monitoring during neurosurgery ByDr. Mai Mohsen Abdel AzizLecturer of anesthesia , Ain Shams University
2The CNS can sometimes be insufficiently monitored leading to grave postoperative complications
3Why 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 systemProvide functional guidance to the surgeon and anesthiologistLocate neural structures (eg. Locate cranial n. during skull base surgery)Reduce morbidity and mortality without introducing additional risks
4What do we want to monitor? A. Monitor of brain electrical activityElectroencephalographyEvoked potentials:I. Sensory evoked potentials. Visual. Somatosensory. AuditoryII. Motor evoked potentials3. Bispectral index
61. Electroencephalography Value:1.Measures electrical function of brain2.Indirectly measures blood flow3.Measures anesthetic effects4.Guide reduction of cerebral metabolism prior to induced reduction of blood flow5.Predict neurologic outcome after brain insult6.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).
73 parameters of the signal: Amplitude – size or voltage of signalFrequency – number of times signal oscillatesTime – duration of the sampling of the signal
8. Epilepsy . Global ischemia Abnormal EEG detectRegional Global. Epilepsy Global ischemia. Focal ischemia . Hypoxemia
9Anesthetic Agents and EEG Light anesthesia : Larger voltage, slower frequencyGeneral anesthesia : Irregular slow activityDeeper anesthesia : Alternating activityVery deep anesthesia : Burst suppression eventually isoelectric
10Anesthetic 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.
11Non-anesthetic Factors Affecting EEG SurgicalCardiopulmonary bypassOcclusion of major cerebral vessel (carotid cross-clamping, aneurysm clipping)Retraction on cerebral cortexSurgically induced emboli to brainPathophysiologic FactorsHypoxemiaHypotensionHypothermiaHypercarbia and hypocarbia
12What to do if EEG technician indicates a possible problem? Check to see if anesthetic milieu is stableRule out hypoxemia, hypotension, hypothermia, hypercarbia and hypocarbiaRaise the MAP, obtain ABGSee if there is a surgical reason
132. Evoked potentials I. Somatosensory evoked potentials (SSEP) What does it monitor?Monitor dorsal column-medial lemniscus pathway to assess spinal cord functionStimulus is applied to a nerve distal to surgical site and recording is made from the cerebral cortex or other locations rostral to surgeryBaseline is obtained, significant changes amplitude >50%Latency >10%
14When 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
15II. Visual evoked potential (VEP) Visual stimuli from flashing diodes in goggles measures intactness of visual pathways from optic nerve to occipital cortexVery sensitive to anesthetic drugs and variable signalsWhen can we use it?Trans-sphenoidal …anterior fossa surgeries…
16III. Auditory evoked potentials (AEP) Auditory signal transmitted to patient follows auditory pathways CN VIII, cochlear nucleus, rostral brain stem, inferior colliculus, auditory cortexIt is resistant to anesthetic drugsWhen do we use it?Decompression of CN VIII…Resection of acoustic neuroma..
17Anesthetic Agents and SEPs Most anesthetic drugs increase latency and decrease amplitudeVolatile agents: increase latency, decrease amplitudeBarbituates: increase in latency, decrease amplitudeExceptions:Nitrous oxide: latency stable, decrease amplitudeEtomidate: increases latency, increase in amplitudeKetamine: increases amplitudeOpiods: no clinically significant changesMuscle relaxants: no changes
18Physiologic Factors and SEP’s HypotensionHyperthermia and hypothermiaHypoxemiaHypercapneaSignificant anemia (HCT <15%)Technical factor: poor electode-to skin-contact and high electrical impedence (eg electrocautery)
19How do we manage?. First rule out systemic factors:improve neural tissue blood flow and nutrient deliveryIntravascular volume and cardiac performance optimized (crystalloid/colloid or blood) to increase oxygen-carrying capacity – optimal HCT 30% or higherElevate MAPBlood gas – assure oxygenation, normocarbia to help improve collateral blood supply if hypocarbicConsider 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
20IV. Motor evoked potentials Spinal cord monitoring esp. motor tracts not covered by SSEP monitoringSubstituted old-fashioned Stagnara wake-up testIt is the reverse of SSEP, motor cortex is stimulated transcraniallyRecordings are made from muscles in the limb or from spinal cord caudal to surgical siteWhen can we use it?Spine surgeries
21Is it sensitive?More sensitive in detecting post-operative motor deficitsIntravenous agents produce significantly less depressionMuscle relaxants interfere
223. Bispectral index (BIS) integrates single-channel EEGThe 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)
23Value? reduce the overall anesthetic dose and its related side effects Decreases the incidence of postoperative awarenessshorten emergence timeand allow early postoperative recovery
24Monitors of blood flow dynamics 1.Transcranial doppler Direct, noninvasive measurement of CBFSound waves transmitted throughthin temporal bone contact blood,are reflected, and detectedMost easily monitor middlecerebral artery
25When 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
262. Cerebral Oximetry (Near infrared spectroscopy) determine cerebral saturationuses 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 determinesthe overall saturationof the blood present withinthe brain tissues.
27Is it sensitive? When is it used ? High intersubject variability Low specificityWhen is it used ?cardiac surgery to detect the cerebral desaturation (20% from the base cerebral saturation) with CPB .carotid endarterectomy
283. 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.
29Analysis 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 CPBrelatively invasive and insensitive technique.has been replaced by noninvasive cerebral oximetery.
304.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 .
31decrease 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
32ConclusionMultimodality 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.