Advances in neuro anesthesia monitoring
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The document discusses various techniques for monitoring the brain during anesthesia to prevent neurological insults. It describes electroencephalography (EEG) techniques like raw EEG, bispectral index, and entropy which can detect cerebral ischemia. It also discusses evoked potentials like somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) using electrical stimulation to assess spinal cord and brain function. Additional monitoring methods covered are intracranial pressure (ICP), cerebral blood flow (CBF), brain oxygenation, and electromyography (EMG) for nerve function. The document emphasizes multimodal monitoring as the gold standard to reduce intraoperative neurological injury.
Advances in neuro anesthesia monitoring
- 1. Advances in Neuro-Anesthesia Monitoring Something in the market? Wesam Farid Mousa Proffessor of Anesthesia & Surgical ICU Tanta University, Egypt
- 2. The anaesthetized brain is vulnerable to ischemic insults, which could result in neuropsychological disturbances, stroke and even death.
- 3. The anesthesiologist plays a pivotal role in instituting neuro protective strategies
- 4. He has to rely on neuromonitoring to prevent intraoperative neurological insult.
- 6. Secondary prevention include early detection of neuro-ischemia Secondary prevention needs efficient monitoring tests and tools. So
- 7. EMG Early detection of surgically induced nerve damage and assessment of level of nerve function intra-operatively. Active or passive. Uses: 1.Facial nerve monitoring 2.Trigeminal nerve monitoring 3.Spinal Accessory nerve The brain can be monitored in terms of:- Function ICP & CBF Brain oxygenation
- 8. EMG Early detection of surgically induced nerve damage and assessment of level of nerve function intra-operatively. Active or passive. Uses: 1.Facial nerve monitoring 2.Trigeminal nerve monitoring 3.Spinal Accessory nerve The brain can be monitored in terms of:- Function ICP & CBF Brain oxygenation
- 9. Monitoring of function:- 1)Wake up test 2) Electroencephalogram EEG Raw EEG Bispectral index Entropy 3) Evoked Potentials: SEP: SSEP Visual Auditory MEP: Transcranial magnetic / Transcranial electric
- 10. Lightening anesthesia during the procedure and observing the patient’s ability to move to command. It was first described in 1973. Disadvantages: Evaluates gross functional integrity of motor pathway Provides information at the time of the wake-up only Does not assess sensory pathways Wake-up test
- 12. Monitoring of function:- 1)Wake up test 2) Electroencephalogram EEG Raw EEG Bispectral index Entropy 3) Evoked Potentials: SEP: SSEP Visual Auditory MEP: Transcranial magnetic / Transcranial electric
- 13. “Recording brain's spontaneous electrical activity over a period of time from multiple electrodes placed on the scalp” Electroencephalography EEG
- 14. Intraoperatively, EEG can be used to : Indirectly measures blood flow Measures anesthetic effects Detect cerebral ischemia
- 15. Intraoperatively, EEG can be used to : Indirectly measures blood flow Measures anesthetic effects Detect cerebral ischemia
- 16. Intraoperatively, EEG can be used to : Measures aneIndirectly measures blood flow sthetic effects Detect cerebral ischemia EEG criteria for ischemic changes e.g. in CEA: Attenuation of 8-15 Hertz activity to minimal or nil and/or Two-fold or more increase of delta activity at one Hertz or less
- 17. Limitation: *Expert encephalographer is required *Affected by Artefacts, Anesthesia, Hypoxemia Hypotension Hypothermia Hyper-Hyporcarbia
- 18. “raw EEG” was converted to a “processed” one that needs less experience to interpret
- 19. Bispectral Index (BIS), Entropy These monitors provide a number derived from EEG, which indicates level for general anesthesia
- 20. BIS
- 21. RE Fast matching parameter used to detect activation of facial muscles SE Used to assess the hypnotic effects of anesthestic drugs on the brain Entropy
- 22. During awake state and induction there is a difference between the two entropies indicating muscle activity on the face
- 23. Decrease in the entropy measurement may enable the anesthetist to observe the moment when patient loses responsiveness
- 24. Both entropies stabilize during the operation. Sudden peaks in RE during surgeryare caused by activation of FEMG
- 25. Burst suppression can be selected on the screen to indicate the silent periods in the EEG
- 26. In patients with raised ICP, where anesthesia is titrated according to BIS or entropy values, they suddenly increases after cranial decompression, reflecting decrease in CPP. 37/33 94/83 40/40 (RE) / (SE) Following the removal of the bone flap Before the removal of the bone flap After increasing anesthetic depth BIS and Entropy can be used as an indirect indicators of increased CBF and ICP
- 27. Detection of Gas Embolism by BIS & Entropy
- 28. Monitoring of function:- 1)Wake up test 2) Electroencephalogram EEG Raw EEG Bispectral index Entropy 3) Evoked Potentials: SEP: SSEP Visual Auditory MEP: Transcranial magnetic / Transcranial electric
- 29. Somatosensory evoked potentials SSEPs Electrical activity of the brain that results from the stimulation of touch
- 30. In the 1970’s, SSEPs were used to avoid paralysis in scoliosis surgeries and became the standard of care for a wide variety of spinal and other surgeries.
- 31. SSEPs provide monitoring to the dorsal columns of spinal cord. The stimulus applied to the peripheral N (tibial or ulnar) Recording electrodes placed: scalp or exposed dura Responses are recorded intermittently during surgery
- 32. SSEPs A reduction in the amplitude by 50% and an increase in the latency by 10% are considered significant. Latency – time from stimulus to onset of SER Amplitude – voltage of recorded response
- 33. Indications Scoliosis correction Spinal cord decompression Brachial plexus exploration Resection of spinal cord tumor Resection of intracranial lesions
- 34. SSEP help to recognize any deterioration in CBF and indicate intermittent reperfusion during: clipping of intracranial aneurysms, carotid endarterectomy and thoracic aortic aneurysm repair,
- 35. Limitations of SSEPs Motor ventral corticospinal tracts are away from the sensory dorsomedial tracts So: It is possible to have normal SSEPs recordings throughout surgery, but to face a paraplegic patient postoperatively.
- 36. During the 1990s, "motor evoked potentials", were recorded from peripheral nerves, following direct electrical stimulation of the spinal cord. Motor evoked potentials MEP
- 37. Central stimulation Direct: exposed motor cortex Transcranial: either magnetic or electrical
- 38. Peripheral responses Myogenic: from muscles Neurogenic: from peripheral nerves or spinal cord
- 39. Transcranial magnetic stimulation is generally unsuitable intraoperatively because it is sensitive to anesthesia Electrical stimulation is painful for clinical use in awake patient Thus, electrical stimulation being the choice for intraoperative monitoring, and magnetic for clinical applications.
- 40. The primary problem that has slowed widespread application of the intraoperative SSEPs and MEPs is anesthetic induced depression
- 42. Multimodal monitoring has become the gold standard of care and is the preferred method for detection and reduction of intraoperative neurological injury.
- 43. Visual Evoked Potential (VEP) Flash stimulation of light changes occipital EEG
- 44. VEP waveform induced by flash stimulation
- 45. Comparison of the average latency of major positive vertices of VEP induced by flash stimulation
- 46. VEP nomenclature is determined by using capital letters stating whether the peak is positive (P) or negative (N) followed by a number which indicates the average peak latency for that particular wave. For example, P100 is a wave with a positive peak at approximately 100 ms following stimulus onset. The average amplitude for VEP waves usually falls between 5 and 20 microvolts. Upward is negative
- 47. A significant decrease in flash VEP is defined as a decrease in peak-to-peak distance between N75 and P100 by at least 50% from the reference amplitude. Flash VEP waveform.
- 48. Beneficial in procedures that could cause postoperative visual impairment, such as prone position, transsphenoidal surgery
- 49. Auditory Evoked Potential (AEP) Repetitive clicks delivered to the ear reflects the VIII nerve & brainstem “well-being”
- 50. Typical AEP record with its subcortical and cortical components
- 51. Beneficial in Procedures near auditory pathway and posterior fossa, decompression of CN VII, resection of acoustic neuroma
- 52. EMG Early detection of surgically induced nerve damage and assessment of level of nerve function intra-operatively. Active or passive. Uses: 1.Facial nerve monitoring 2.Trigeminal nerve monitoring 3.Spinal Accessory nerve The brain can be monitored in terms of:- Function CBF & ICP Brain oxygenation
- 53. Monitoring of ICP:- Invasive 1.Intraventricular catheter 2.Subdural catheter 3.Epidural sensor 4.Subdural screw (blot) 5.Intraparynchymal sensor Non-invasive 1.Non-contrast CT scan 2.MRI 3.TCD 4.Tympanic membrane displacement 5.Optic nerve sheath diameter
- 54. INTRAVENTRICULAR CATHETER -Most accurate monitoring method -A hole is drilled through the skull. The catheter is inserted through the brain into the lateral ventricle -Can also be used to drain fluid out
- 55. Subdural Catheter •Inserted through a hole drilled in the skull •No parynchymal injury •An epidural sensor is inserted between the skull and dura
- 56. Epidural Sensor •Inserted through a hole drilled in the skull •An epidural sensor is inserted between the skull and dura •Allows recording not drainage
- 57. Subdural Screw (BOLT) Inserted through a hole drilled in the skull It is placed through the dura. Allows recording not drainage
- 58. Intraparynchymal fiberoptic device It has no chance of catheter occlusion or leakage Neurological injury is minimal because of small probe diameter Allows recording not drainage
- 59. ICP waveforms ICP shows a pulsatile recording with slow respiratory component superimposed on a biphasic recording synchronous with cardiac cycle P1 (correlating with the arterial pulse); P2 (relating to the cerebral compliance); P3 (corresponding to aortic valve closure)
- 61. Monitoring of ICP:- Invasive 1.Intraventricular catheter 2.Subdural catheter 3.Epidural sensor 4.Subdural screw (blot) 5.Intraparynchymal sensor Non-invasive 1.Non-contrast CT scan 2.MRI 3.TCD 4.Tympanic membrane displacement 5.Optic nerve sheath diameter
- 62. Non-contrast CT scan fast cost-effective - Gross evaluation - Difficult to repeat Findings suggestive of a high ICP include cerebral oedema, midline shift, effacement of basal cisterns, loss of grey-white differentiation, and loss of normal gyri and sulci pattern
- 63. Dynamic MRI This method utilizes the fluctuations in intracranial volume occur with each heartbeat. A mean ICP value is then derived from the linear relationship between ICP and elastance (a change in pressure due to a small change in volume). The MRI study provides a single time point measurement The change in pressure dP due to change in unit volume dV (=Elastance) increases linearlywith increased ICP
- 64. TCD Elevated ICP can be estimated from TCD as it impedes CBF and consequently decreases the blood flow velocity Requires training and inter-observer variations may be seen
- 65. Changes in TCD flow velocity waveform associated with a progressive increase in ICP
- 66. Tympanic membrane displacement (TMD) Increase in ICP is directly transmitted to the footplate of the stapes and thereby affecting the response to a sound and hence audiogram Inaccurate of ± 15 mm Hg, which is not sufficient for a reliable assessment of ICP
- 67. Optic nerve sheath diameter (ONSD) Optic nerve is a part of CNS and the space between the optic nerve and its sheath is a continuation of the subarachnoid space, filled with CSF, whose pressure is equal to the ICP
- 68. Optic nerve sheath diameter In increased ICP, the ONSD increases, and the blood flow through the central retinal vein that courses through the sheath gets impeded (causing papilloedema).
- 69. Optic nerve sheath diameter Can be conveniently measured by transocular sonography >5 mm corresponding to an ICP of 20 mm Hg or higher.
- 70. Monitoring of CBF Transcranial doppler sonography Thermal diffusion cerebral blood flow monitoring
- 71. Measure flow velocity in MCA, and thus CBF Sensitive method to detect cerebral emboli Doubtful efficacy in detecting cerebral ischemia Transcranial doppler sonography (TCD)
- 72. The rate at which heat dissipates in a tissue depends on the tissue’s thermal conductive properties and the blood flow in that area. Thermal diffusion cerebral blood flow monitoring
- 73. Flexible catheter with two thermistors (proximal & distal) Distal thermistor is heated to 2°C above tissue temp. Power dissipated by the heated thermistor provides a direct measure of the tissue’s ability to transport heat. The proximal thermosensor is located outside the thermal field allowing continuous monitoring of tissue temperature
- 74. EMG Early detection of surgically induced nerve damage and assessment of level of nerve function intra-operatively. Active or passive. Uses: 1.Facial nerve monitoring 2.Trigeminal nerve monitoring 3.Spinal Accessory nerve The brain can be monitored in terms of:- Function CBF & ICP Brain oxygenation
- 75. Monitoring of cerebral oxygenation Direct brain tissue partial pressure oxygen monitoring Cerebral microdialysis brain tissue biochemistry Jugular bulb venous oximetry monitoring Near Infrared Spectroscopy (NIRS)
- 76. Tissue partial pressure oxygen monitoring A catheter is placed into the brain tissue through drill hole into the subcortical white matter
- 77. The diffusion of oxygen molecules through an oxygen-permeable membrane into an electrolyte solution causes an electric current that is proportional to Po2.
- 78. In patients with cerebral ischaemia the values are 10 ± 5 mmHg as against 37 ± 12 mmHg in normal individuals
- 79. Cerebral microdialysis brain tissue biochemistry Small catheter inserted with ICP/tissue PO2 monitor
- 80. 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 ○Glutamate: neuronal injury a
- 81. Jugular venous oximetry Continuous monitoring of jugular venous oxygen saturation (SjVO2 ) is carried out by a catheter placed retrograde through the internal jugular vein into the jugular bulb.
- 82. 1.Jugular venous oxygen saturation (SjVO2) 2.Cerebral arteriovenous oxygen difference (A-VDO2) (difference between arterial and jugular venous oxygen content) 3.Cerebral oxygen extraction(CEO2) (the difference between SaO2 and SjVO2). Indices obtained from SjVO2
- 83. Near infrared spectroscopy “NIRS” “cerebral oximetry” cerebral oximetry is non-invasive and continuous “real-time” detection of cerebral oxygen saturation (SctO2)
- 84. Light travels from the sensor’s light emitting diode to either a proximal or distal detector, permitting separate data processing of shallow and deep optical signals
- 85. Thus, cerebral oximetry measures venous and arterial blood and includes contributions from both of them in a 3:1 ratio
- 86. Data from the scalp and surface tissue are subtracted and suppressed, reflecting rSO2 in deeper tissues
- 88. LIMITATIONS: the sensors are placed over the frontal lobes and cannot detect involvement of other brain parts
- 89. LIMITATIONS: What is the cause Know how Different Organs Behave Under Different Conditons Ischemia (Poor Flow) Vs Hypoxia (No Oxygen) Vs Venous Congestion