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Questions and Answers
What is considered significant regarding SSEP signals?
What is considered significant regarding SSEP signals?
Which cranial nerves are classified as motor only?
Which cranial nerves are classified as motor only?
What does a significant increase in BAEP latency indicate?
What does a significant increase in BAEP latency indicate?
What should be avoided during neural monitoring with NIM ETTs?
What should be avoided during neural monitoring with NIM ETTs?
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Which monitoring technique correlates flow velocity and flow itself for cerebral blood flow?
Which monitoring technique correlates flow velocity and flow itself for cerebral blood flow?
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Which factor does NOT influence cerebral blood flow (CBF)?
Which factor does NOT influence cerebral blood flow (CBF)?
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What is a significant limitation of Transcranial Doppler (TCD) monitoring?
What is a significant limitation of Transcranial Doppler (TCD) monitoring?
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During which procedure is TCD monitoring primarily utilized for detecting ischemia and microemboli?
During which procedure is TCD monitoring primarily utilized for detecting ischemia and microemboli?
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Which of the following statements about microdialysis catheters is correct?
Which of the following statements about microdialysis catheters is correct?
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Indocyanine Green Video Angiography is primarily used for which type of assessment?
Indocyanine Green Video Angiography is primarily used for which type of assessment?
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What is the typical failure rate of Transcranial Doppler in the operating room?
What is the typical failure rate of Transcranial Doppler in the operating room?
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What does intracranial volume consist of?
What does intracranial volume consist of?
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Which aspect of cerebral blood flow monitoring is still considered to be evolving?
Which aspect of cerebral blood flow monitoring is still considered to be evolving?
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Which is NOT a clinical indication for TCD monitoring?
Which is NOT a clinical indication for TCD monitoring?
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What characterizes the qualitative assessment capabilities of TCD?
What characterizes the qualitative assessment capabilities of TCD?
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What is a primary goal of neuromonitoring during anesthesia?
What is a primary goal of neuromonitoring during anesthesia?
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Which monitoring technique specifically measures electrical activity in the brain?
Which monitoring technique specifically measures electrical activity in the brain?
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What waveform is dominant in an awake EEG, indicating high frequency and low amplitude?
What waveform is dominant in an awake EEG, indicating high frequency and low amplitude?
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Which of the following is a common category of neurophysiologic monitors?
Which of the following is a common category of neurophysiologic monitors?
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What EEG pattern indicates a state of suppressed electrical activity due to increased ischemia or hypoxia?
What EEG pattern indicates a state of suppressed electrical activity due to increased ischemia or hypoxia?
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What factor is critical to the functioning of EEG monitoring?
What factor is critical to the functioning of EEG monitoring?
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What is the main purpose of intraoperative neuromonitoring?
What is the main purpose of intraoperative neuromonitoring?
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Which of the following EEG waveforms is typically associated with deep coma or severe metabolic disturbance?
Which of the following EEG waveforms is typically associated with deep coma or severe metabolic disturbance?
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What EEG interpretation outcome reflects a condition of prolonged oxygen deficiency?
What EEG interpretation outcome reflects a condition of prolonged oxygen deficiency?
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Which monitoring technique specifically measures cerebral blood flow (CBF)?
Which monitoring technique specifically measures cerebral blood flow (CBF)?
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What advantage does the use of Transcranial Doppler sonography provide?
What advantage does the use of Transcranial Doppler sonography provide?
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Which wave pattern indicates decreased brain activity and is pertinent during anesthesia monitoring?
Which wave pattern indicates decreased brain activity and is pertinent during anesthesia monitoring?
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What is the primary concern related to patients with neurologic diseases undergoing surgery?
What is the primary concern related to patients with neurologic diseases undergoing surgery?
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What monitoring technique is utilized to assess brain metabolism non-invasively?
What monitoring technique is utilized to assess brain metabolism non-invasively?
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Which method primarily utilizes a catheter for continuous monitoring of intracranial pressure (ICP)?
Which method primarily utilizes a catheter for continuous monitoring of intracranial pressure (ICP)?
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Which monitoring technique is employed to determine cerebral blood flow (CBF) using Doppler principles?
Which monitoring technique is employed to determine cerebral blood flow (CBF) using Doppler principles?
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Which EEG wave pattern is typically observed during deep sleep or anesthesia, characterized by low frequency and low to high amplitude?
Which EEG wave pattern is typically observed during deep sleep or anesthesia, characterized by low frequency and low to high amplitude?
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What type of monitor categorizes EEG, evoked potentials, and electromyography?
What type of monitor categorizes EEG, evoked potentials, and electromyography?
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Which parameter is critical for assessing the patient's metabolic needs during anesthesia monitoring?
Which parameter is critical for assessing the patient's metabolic needs during anesthesia monitoring?
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What is a key feature of absolute cerebral blood flow (CBF) monitors?
What is a key feature of absolute cerebral blood flow (CBF) monitors?
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Which type of monitoring technique is NOT primarily associated with detecting changes in intracranial pressure (ICP)?
Which type of monitoring technique is NOT primarily associated with detecting changes in intracranial pressure (ICP)?
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Which monitoring technique allows for the discrimination of cerebral blood flow in specific regions compared to overall flow?
Which monitoring technique allows for the discrimination of cerebral blood flow in specific regions compared to overall flow?
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What type of EEG waves are typically observed in a state of relaxed wakefulness?
What type of EEG waves are typically observed in a state of relaxed wakefulness?
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What is an important characteristic of monitors used for assessing neural integrity?
What is an important characteristic of monitors used for assessing neural integrity?
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Study Notes
Goals of Neuroanesthesia
- Goal of neuroanesthesia is to provide sufficient oxygen and glucose to fulfill the brain's metabolic demands.
- Perioperative goals:
- Ensure a favorable supply/demand relationship by controlling brain hemodynamics.
- Prevent brain herniation when the skull is closed, using techniques like hyperventilation.
- Provide relaxation with neuromuscular blocking agents (NMB) to reduce demand.
Importance of Neuromonitoring
- Patients undergoing neurosurgical procedures with neurologic disease have an increased risk of ischemic and hypoxic damage.
- Intraoperative monitoring may improve patient outcomes.
- Early detection aids in tailoring anesthetic and surgical procedures to patient status.
Routine Anesthesia Monitors
- Electrocardiogram (ECG)
- Non-invasive blood pressure (NIBP)
- Fraction of inspired oxygen (FiO2)
- End-tidal carbon dioxide (EtCO2)
- Oxygen saturation (SaO2)
- Precordial or esophageal stethoscope
Expanded Anesthesia Monitors
- Arterial pressure monitoring
- Central venous pressure (CVP) monitoring
- Pulmonary artery (PA) monitoring
- Precordial Doppler
3 Categories of Neurophysiologic Monitors
-
Monitors of function:
- Electroencephalogram (EEG)
- Evoked potentials
- Electromyography (EMG)
-
Monitors of blood flow:
- Nitrous oxide wash-in
- Radioactive xenon clearance
- Laser Doppler blood flow
- Transcranial Doppler sonography
- Microvascular Doppler ultrasound
- Indocyanine green videoangiography
- Intracranial pressure (ICP) alone
- Intraventricular catheter
- Fiberoptic parenchymal catheter
- Subarachnoid bolt
- Epidural catheter
-
Monitors of metabolism:
- Invasive: intracerebral PO2 electrode
- Non-invasive:
- Transcranial cerebral oximetry (near-infrared spectroscopy)
- Jugular venous oximetry
Monitors of Function - EEG
- EEG measures electrical activity of the brain, specifically the pyramidal cells in the cerebral cortex.
- EEG is dependent on an adequate supply of oxygen and glucose.
- Electrode placement follows the International 10:20 system for standardization and consistency.
- Letters: F (frontal), T (temporal), C (central), P (parietal), O (occipital)
- Distance: 10% or 20% of total front to back or left to right side of the skull.
- Evens: right hemisphere
- Odds: left hemisphere
- Nasion: depressed area between the eyes
- Inion: lowest point of the skull
- EEG interpretation considers amplitude (height), wave shapes, and frequencies (fast or slow).
- Beta wave: high frequency, low amplitude, dominant during awake state.
- Alpha wave: medium frequency, higher amplitude, seen in the occipital cortex with eyes closed while awake (relaxation).
- Theta wave: low frequency, not predominant in any condition, seen in general anesthesia (GA) and children during sleep.
- Delta wave: very low frequency, low to high amplitude, signifies depressed functions, consistent with deep coma, anesthesia, metabolic factors, or hypoxia.
- EEG is a reflection of the brain's wakefulness and metabolic activity.
- Depression of the EEG is caused by a decrease in blood flow, oxygen, or glucose.
- Hypoxia/ischemia leads to:
- Transient increase in beta activity.
- Slow waves (theta) with large amplitude.
- Disappearance of beta activity.
- Delta waves with low amplitude (representing suppression).
- EEG states of awareness
- Abnormal EEG patterns:
- Generalized slowing (background slowing, intermittent slowing, continuous slowing)
- Focal or localized slow activity
- More severe patterns: periodic patterns (burst suppression, background suppression, electro-cerebral inactivity (ECI))
- Abnormal EEG patterns:
- Continued ischemia/hypoxia can progress to:
- Suppression of electrical activity → burst suppression.
- Complete flat electrical silence = flat EEG.
- This signifies the beginning of irreversible brain damage.
- Burst suppression is a significant finding that requires immediate action by the anesthesia team.
- A 10% increase in latency of somatosensory evoked potentials (SSEP) signals is significant in some centers.
- Increased latency of brainstem auditory evoked potentials (BAEP) > 2 milliseconds is significant.
Monitors of Function - Electromyography (EMG)
- Operations in the posterior fossa and lower brain stem have a high potential for injury to the cranial nerves.
- Cranial nerves with motor components (3, 4, 5, 6, 7, 9, 10, 11, 12) are monitored during surgery.
- Motor-only cranial nerves: (3, 4, 6, 11, 12) are monitored with EMG.
- Monitoring EMG helps to identify and preserve cranial nerves by recording their integrity.
Neural Nerve Integrity Monitoring with NIM ETTs
- Two types of potentials, spontaneous and evoked, can be recorded.
- Spontaneous activity helps detect injury potential.
- Evoking the nerve with electrical stimulations helps identify and preserve the cranial nerve.
- During this type of monitoring, neuromuscular blocking agents (NMBAs) cannot be used.
- This monitoring helps to prevent injury to laryngeal nerves, particularly the recurrent laryngeal nerve (RLN).
Monitors of CBF/ICP
- Absolute cerebral blood flow (CBF) monitors:
- Provide real-time continuous perfusion
- Correlate flow velocity and flow itself.
- Relative CBF monitors:
- Compare flow in an area with the total blood flow.
- Laser Doppler flowmetry
- Transcranial Doppler ultrasonography
- Limitations:
- Volume of tissue monitored is limited to 1 mm.
- Requires a burr hole for insertion.
- Limited use currently.
- ICP Monitors
Review of CBF
- CBF is determined by:
- Blood viscosity.
- Vessel length.
- Degree of dilation of the blood vessel (radius).
- CBF is influenced by:
- Cerebral perfusion pressure (CPP).
- Body temperature.
- Blood gas content.
- Cardiac output.
- Altitude.
- Autoregulation and flow metabolism coupling.
- Chemical mediators.
Monitoring of CBF and ICP - Transcranial Doppler (TCD)
- TCD measures CBF velocity in the Circle of Willis noninvasively and continuously.
- Intraoperatively, the middle cerebral artery is measured by placing a probe over the zygomatic arch.
- TCD provides a qualitative assessment of ICP.
- Detects air/particulate emboli.
- TCD sonography measures relative changes in CBF and provides a qualitative assessment of ICP/CPP.
- It can be used to determine cerebral autoregulation and CO2 reactivity.
- TCD cannot measure CBF.
Clinical Intraoperative Indications for Transcranial Doppler Monitoring
- Carotid endarterectomy for detection of ischemia and/or microemboli.
- Diagnosis and treatment of postoperative hyperperfusion syndrome.
- Diagnosis and treatment of postoperative intimal flap or thrombosis.
- Cardiac surgery: Cerebral emboli detection during cardiopulmonary bypass (CPB) and cerebral perfusion during CPB (validity for this purpose is still unclear).
- Closed head injury: to assess autoregulation and diagnose hyperemia and vasospasm.
- May be useful in head injured patients undergoing non-neurosurgical procedures.
Limitations of TCD in the OR
- Most monitors are designed as diagnostic tools.
- A fixation device is required, interfering with the procedure and preventing continuous, reliable recording.
- Skill and training is required.
- Successful ultrasound transmission through the skull depends on the thickness of the skull.
- Failure rate is 5-20%.
Microdialysis Catheters
- Semi-quantitative technique.
- 20 MHz probe applied directly to the surface of the vessel.
- Used to determine vessel patency and flow in the aneurysmal sac during aneurysm repair.
- Enables sampling and collecting from the interstitial space.
- Monitors and quantifies neurotransmitters, neuropeptides, hormones, and other molecules in brain interstitial tissue fluid.
Indocyanine Green Video Angiography
- Qualitative technique to assess blood flow during aneurysm surgery.
- Complements the microvascular Doppler ultrasound.
- Removes the need for intraoperative angiography to determine parent vessel patency and placement of clips postoperatively.
- Used in:
- Spinal surgery involving vascular lesions, aneurysm, and arteriovenous malformation (AVM) repair.
- Extracranial-intracranial (EC-IC) bypass surgeries.
Intracranial Pressure Measurement
- Supratentorial pressures are measured in the lateral ventricle and subarachnoid space over the convexity of the cerebral cortex.
- Intracranial volume consists of:
- Brain tissue.
- Blood volume.
- Cerebrospinal fluid (CSF) volume.
Importance of Intracranial Pressure Monitoring
- It influences patient outcomes.
- It aids in the management of patient care.
- Early detection of changes helps to optimize cerebral perfusion pressure.
Goals of Neuroanesthesia
- Overall goal: Ensure adequate oxygen and glucose supply to meet the brain's metabolic demands.
-
Perioperative goals:
- Maintain a favorable supply/demand relationship by controlling brain hemodynamics.
- Prevent brain herniation during skull closure.
- Provide relaxation to reduce metabolic demand.
Importance of Neuromonitoring
- Increased risk of ischemic or hypoxic damage to the CNS in patients with neurological diseases undergoing surgery.
- Intraoperative monitoring improves patient outcomes through early detection and tailoring anesthetic and surgical procedures to patient status.
Routine Anesthesia Monitors
- Electrocardiogram (ECG)
- Non-invasive blood pressure (NIBP)
- Fraction of inspired oxygen (FiO2)
- End tidal carbon dioxide (EtCO2)
- Oxygen saturation (SaO2)
- Precordial or esophageal stethoscope
Expanded Anesthesia Monitors
- Arterial pressure monitoring
- Central Venous Pressure (CVP) monitoring
- Pulmonary Artery (PA) monitoring
- Precordial Doppler (used in neurological and sitting cases)
Categories of Neurophysiologic Monitors
-
Monitors of Function:
- Electroencephalography (EEG)
- Evoked potentials
- Electromyography (EMG)
-
Monitors of Blood Flow:
- Nitrous Oxide wash-in
- Radioactive xenon clearance
- Laser Doppler blood flow
- Transcranial Doppler sonography
- Microvascular Doppler ultrasound
- Indocyanine green videoangiography
- Intracranial pressure (ICP) monitoring:
- Intraventricular catheter (most common)
- Fiberoptic parenchymal catheter
- Subarachnoid bolt
- Epidural catheter
-
Monitors of Metabolism:
- Invasive: Intracerebral PO2 electrode (Paratrend, Licox)
-
Non-invasive:
- Transcranial cerebral oximetry (near infrared spectroscopy)
- Jugular venous oximetry
EEG
-
Measures the electrical activity of the brain.
-
Produced by pyramidal cells in the cerebral cortex, providing no information about subcortical tissue, spinal cord, or cranial nerves.
-
Dependent on adequate oxygen and glucose supply.
-
Monitored from the scalp and forehead using surface or needle electrodes.
-
Electrode placement follows the international 10:20 system.
-
Amplitude, wave shapes, and frequencies are analyzed.
-
Waveforms:
- Beta wave: 13-30 Hz, high frequency, low amplitude, dominant during awake state.
- Alpha wave: 9-12 Hz, medium frequency, higher amplitude, seen in the occipital cortex with eyes closed while awake.
- Theta wave: 4-8 Hz, low frequency, not predominant in any condition.
- Delta wave: 0-4 Hz, very low frequency, low to high amplitude, signifies depressed functions.
-
Waveforms:
-
EEG interpretation:
- Reflects the brain's wakefulness and metabolic activity.
- Represents the summation of excitatory and inhibitory postsynaptic potentials of pyramidal cells.
- Depression of the EEG indicates a decrease in blood flow, oxygen, or glucose.
- Awake EEG shows predominantly beta activity.
- Hypoxia or ischemia leads to:
- Transient increase in beta activity
- Slow waves (theta) with large amplitude
- Disappearance of beta activity
- Delta waves with low amplitude.
-
EEG States of Awareness: These are not specifically described in the text.
-
Abnormal EEG patterns:
- Generalized slowing: background slowing, intermittent slowing, continuous slowing.
- Focal or localized slow activity.
- More severe patterns: periodic patterns, burst suppression, background suppression, electrocerebral inactivity (ECI).
-
Ischemia/Hypoxia and EEG interpretation:
- Continued ischemia or hypoxia can progress to suppression of electrical activity, resulting in burst suppression.
- Ultimately, complete flat electrical silence (flat EEG) represents the beginning of irreversible brain damage.
-
Burst suppression:
- Technician informs the surgeon.
- Surgeon adjusts surgical approach to minimize nerve damage.
Electromyography (Cranial Nerve Function)
- Operations in the posterior fossa and lower brainstem have a high potential for injury to the cranial nerves.
- Cranial nerves with motor components: 3, 4, 5, 6, 7, 9, 10, 11, 12.
- Cranial nerves with only motor function: 3, 4, 6, 11, 12.
-
Monitoring EMG potential for motor cranial nerves:
- Allows for monitoring and recording the integrity of the nerves.
- Protects against nerve damage.
Neural Nerve Integrity Monitoring with NIM ETTs
- Two types of potentials (spontaneous and evoked) can be recorded.
- Spontaneous activity: injury potential can be detected when a surgical instrument approaches a cranial nerve.
- Evoked activity: electrical stimulation helps identify and preserve cranial nerves.
- During NIM monitoring, neuromuscular blocking agents cannot be used due to risks of facial drooping or vocal hoarseness.
- This monitoring helps prevent injury to laryngeal nerves, particularly the Recurrent Laryngeal Nerve (RLN).
Monitors of Cerebral Blood Flow (CBF) and Intracranial Pressure (ICP)
-
Absolute CBF monitors: provide real-time continuous perfusion measurements.
-
Relative CBF monitors: compare flow in a specific area to total blood flow.
- Laser Doppler flowmetry: surface probe that measures local CBF.
- Transcranial Doppler ultrasonography: limitations include limited volume of tissue monitored and requirement of a burr hole.
-
ICP monitors: Various methods are used, including:
- Intraventricular catheter
- Fiberoptic parenchymal catheter
- Subarachnoid bolt
- Epidural catheter
Review of CBF
-
Determined by:
- Blood viscosity
- Vessel length
- Degree of dilation of the blood vessel
-
Influenced by:
- Cerebral perfusion pressure (CPP)
- Body temperature
- Blood gas content
- Cardiac output
- Altitude
- Autoregulation and flow metabolism coupling
-
Chemical mediators can also influence CBF.
Transcranial Doppler (TCD)
- Measures CBF velocity non-invasively and continuously in the Circle of Willis.
- During surgery, the middle cerebral artery is monitored by placing a probe over the zygomatic arch.
- Qualitative assessment tools for ICP
- Useful for detecting air/particulate emboli.
-
Clinical indications for TCD monitoring:
- Carotid endarterectomy
- Detection of ischemia and/or microemboli
- Diagnosis and treatment of postoperative hyperperfusion syndrome
- Diagnosis and treatment of postoperative intimal flap or thrombosis
- Cardiac surgery
- Cerebral emboli detection during cardiopulmonary bypass (CPB)
- Cerebral perfusion during CPB
- Closed head injury
-
Limitations of TCD in the OR:
- Most monitors are designed for diagnostic purposes.
- A fixation device is required, which can interfere with the procedure.
- Skill and training are required.
- Ultrasound transmission through the skull depends on its thickness, leading to a 5-20% failure rate.
Microdialysis Catheters
- Semi-quantitative technique.
- A 20 MHz probe is applied directly to the surface of the vessel. - Allows neurosurgeons to determine vessel patency and flow in the aneurysmal sac during aneurysm repair.
- Enables sampling and collecting from the interstitial space.
- Monitors neurotransmitters, neuropeptides, hormones, and other molecules in brain interstitial tissue fluid.
Indocyanine Green Video Angiography
- Qualitative technique for assessing blood flow during aneurysm surgery.
- Used to complement microvascular Doppler ultrasound and remove the need for intraoperative angiography.
-
Uses:
- Spinal surgery involving vascular lesions, aneurysm, and arteriovenous malformation (AVM) repair.
- Extracranial-intracranial bypass surgeries.
Intracranial Pressure Measurement
- Supratentorial pressures are measured in the:
- Lateral ventricle
- Subarachnoid space over the convexity of the cerebral cortex
- Intracranial volume consists of:
- Brain tissue
- Blood volume
- Cerebrospinal fluid (CSF) volume
Why is Intracranial Pressure Monitoring Important in Neuroanesthesia?
- ICP monitoring helps manage pressure changes and prevent brain herniation.
- Elevated ICP compromises cerebral perfusion and can lead to neurological damage.
- ICP monitoring allows for early identification of potential issues and interventions.
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Description
This quiz covers the fundamental goals of neuroanesthesia, including oxygen delivery and brain protection during surgeries. It also discusses the significance of neuromonitoring in improving patient outcomes and the routine anesthesia monitors used in the operating room.
