LHSC Anesthesiology

1. 02/2009 LHSC Anesthesiology 1 Neuromonitoring in the Operating Room Dr. Gary Simon

2. 02/2009 LHSC Anesthesiology 2 Introduction Define neuromonitoring Risk of CNS damage Spinal cord anatomy Mechanisms of injury

3. 02/2009 LHSC Anesthesiology 3 Introduction Stagnara and Clonus testing Somatosensory evoked potentials Motor evoked potentials Electromyography

4. 02/2009 LHSC Anesthesiology 4 Define neuromonitoring Ensure that functional integrity is maintained Identify anatomical structures Detect injury patterns The SSEP also has been effective for assessing the viability of specific neural pathways (particularly identification of ischemia). Like EEG, SSEP remains normal until cortical blood flow is reduced to about 20 cc/min/100 g and is altered and then lost at blood flows between 15 and 18 cc/min/100 g, levels above those associated with irreversible cell death. Thus during axial surgery, SSEP monitoring can identify hypoperfusion caused by deliberate hypotension or anemia from hemodilution before permanent injury. Levels of hypotension or anemia not usually associated with injury may in a specific individual cause neuron damage and permanent injury if not corrected Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * The SSEP also has been effective for assessing the viability of specific neural pathways (particularly identification of ischemia). Like EEG, SSEP remains normal until cortical blood flow is reduced to about 20 cc/min/100 g and is altered and then lost at blood flows between 15 and 18 cc/min/100 g, levels above those associated with irreversible cell death. Thus during axial surgery, SSEP monitoring can identify hypoperfusion caused by deliberate hypotension or anemia from hemodilution before permanent injury. Levels of hypotension or anemia not usually associated with injury may in a specific individual cause neuron damage and permanent injury if not corrected Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD *

5. 02/2009 LHSC Anesthesiology 5 Risk of CNS damage Elective AAA (0.16%-0.25%) Scoliosis instrumentation (0.4%-1.6%) Coarctation of the aorta (0.4%-1.5%) Thoraco-abdominal aneurysm (16%-25%) Risk factors: dissection, hypotension, long period of aortic crossclamping, increased ICP, sacrifice of critical intercostal or lumbar arteries, and extent of aortic disease Thoraco-abdominal aneurysm spinal cord injury risk factors: dissection, hypotension, long period of aortic crossclamping, increased ICP, sacrifice of critical intercostal or lumbar arteries, and extent of aortic disease.Thoraco-abdominal aneurysm spinal cord injury risk factors: dissection, hypotension, long period of aortic crossclamping, increased ICP, sacrifice of critical intercostal or lumbar arteries, and extent of aortic disease.

6. 02/2009 LHSC Anesthesiology 6 High risk scoliosis procedures Combined anterior and posterior repair Hyperkyphosis Significant rigid curves Neuromuscular vs idiopathic

7. 02/2009 LHSC Anesthesiology 7 Spinal cord injury Ischemia, disruption, compression, concussion, or distraction. Type, intensity, location and duration of injury determines the extent of damage. Experienced neuromonitoring teams can decrease deficits by 50% for scoliosis surgery (ie 0.46% vs 1.04 %) Unable to reverse spinal cord tumor resection deficits.Unable to reverse spinal cord tumor resection deficits.

8. 02/2009 LHSC Anesthesiology 8 Spinal cord and brain anatomy Gray and white matter Motor and sensory Anterior and posterior spinal arteries Low thoracic/lumbar blood supply Anterior horn cell

9. 02/2009 LHSC Anesthesiology 9 Brain sensory & motor areas Precentral and postcentral gyrusPrecentral and postcentral gyrus

10. 02/2009 LHSC Anesthesiology 10 Brain sensory & motor areas

11. 02/2009 LHSC Anesthesiology 11 Brain anatomy

12. 02/2009 LHSC Anesthesiology 12 Spine Anatomy Grey and white matter The organization of the spinal cord is elegant. In cross-section, it looks like a butterfly on an oval background. The butterfly shape in the middle of the cord, or the gray matter, contains nerve cell bodies, and the surround, or white matter, has the axons, extensions from nerve cells that carry messages. In unstained tissue, the white matter appears white because axons are wrapped with an fatty insulating substance called myelin. Grey and white matter The organization of the spinal cord is elegant. In cross-section, it looks like a butterfly on an oval background. The butterfly shape in the middle of the cord, or the gray matter, contains nerve cell bodies, and the surround, or white matter, has the axons, extensions from nerve cells that carry messages. In unstained tissue, the white matter appears white because axons are wrapped with an fatty insulating substance called myelin.

13. 02/2009 LHSC Anesthesiology 13 In the section shown, axons are stained dark purple and the gray matter appears red. In the section shown, axons are stained dark purple and the gray matter appears red.

14. 02/2009 LHSC Anesthesiology 14 Sensory and motor pathways to and from the brain Three sensory modalities: Discriminative touch Touch, pressure and vibration Pain and temperature Free nerve endings are responsive to nerve damage, prostaglandins, histamine and substance P Proprioception It is thought that the incoming volley of neural activity from the upper extremity represents primarily the activity in the pathway of discriminative touch (proprioception and vibration) Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * modality It is thought that the incoming volley of neural activity from the upper extremity represents primarily the activity in the pathway of discriminative touch (proprioception and vibration) Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * modality

15. 02/2009 LHSC Anesthesiology 15 Discriminative touch Enter the cord and ascend on the ipsilateral side Synapse in the medulla and cross to the contralateral side Secondary afferents project to the ventroposterior lateral nucleus where they synapse and ascend to the cortex Therefore an injury on the ipsilateral side will be picked up on the contralateral cortex.Therefore an injury on the ipsilateral side will be picked up on the contralateral cortex.

16. 02/2009 LHSC Anesthesiology 16 Therefore an ipsilateral injury to the cord would result in changes on the ipsilateral cortex.Therefore an ipsilateral injury to the cord would result in changes on the ipsilateral cortex.

17. 02/2009 LHSC Anesthesiology 17 MEP requires direct stimulation of the motor cortex [29]. Transcranial stimulation can be achieved by either focused magnetic or electrical energy. This produces EMG responses through the motor pathway (Fig. 2). Cortical pyramidal cells are activated directly (producing descending D waves) or indirectly (producing descending I waves). Waves can travel down the spinal axonal motor pathways and be monitored with epidural electrodes. These responses temporally summate at the anterior horn cells and produce a peripheral nerve response that activates a compound muscle action potential, the more commonly used EMG response using needle pairs near the muscles [30]. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * MEP requires direct stimulation of the motor cortex [29]. Transcranial stimulation can be achieved by either focused magnetic or electrical energy. This produces EMG responses through the motor pathway (Fig. 2). Cortical pyramidal cells are activated directly (producing descending D waves) or indirectly (producing descending I waves). Waves can travel down the spinal axonal motor pathways and be monitored with epidural electrodes. These responses temporally summate at the anterior horn cells and produce a peripheral nerve response that activates a compound muscle action potential, the more commonly used EMG response using needle pairs near the muscles [30]. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD *

18. 02/2009 LHSC Anesthesiology 18 Spinal cord vascular supply Spinal cord vascular supply: Chest Mar 1996 Spinal cord blood supply is from arteries of the brain and from spinal branches of the subclavian, aorta, and iliac arteries. The spinal arteries enter the intervertebral foramina, cross the epidural space and enter the subarachnoid space to get to the spinal cord. * The vascular supply of the spinal cord is from two sources. The anterior spinal artery supplies the ventral 2/3 while the posterior spinal arteries supplies the dorsal sensory part of the spine. There are no communicating branches between the anterior and posterior spinal arteries. Two posterior spinal arteries arise from the posterior cerebellar arteries and descend along the spine sending blood vessels to the posterior white columns and the remainder of the gray posterior columns. These arteries are fed by 25-40 radicular arteries. The anterior spinal artery is a single midline artery formed from branches of each vertebral artery. Unlike the continuous posterior spinal artery, the anterior spinal artery is discontinuous and supplies the spinal cord in a segmental fashion.Spinal cord vascular supply: Chest Mar 1996 Spinal cord blood supply is from arteries of the brain and from spinal branches of the subclavian, aorta, and iliac arteries. The spinal arteries enter the intervertebral foramina, cross the epidural space and enter the subarachnoid space to get to the spinal cord. * The vascular supply of the spinal cord is from two sources. The anterior spinal artery supplies the ventral 2/3 while the posterior spinal arteries supplies the dorsal sensory part of the spine. There are no communicating branches between the anterior and posterior spinal arteries. Two posterior spinal arteries arise from the posterior cerebellar arteries and descend along the spine sending blood vessels to the posterior white columns and the remainder of the gray posterior columns. These arteries are fed by 25-40 radicular arteries. The anterior spinal artery is a single midline artery formed from branches of each vertebral artery. Unlike the continuous posterior spinal artery, the anterior spinal artery is discontinuous and supplies the spinal cord in a segmental fashion.

19. 02/2009 LHSC Anesthesiology 19 Spinal cord vascular supply It descends to the bottom of the cord and only about 6-7 of the radicular arteries supplies the anterior spinal artery.. Lower thoracic anterior cord has the poorest blood supply � typically one radicular artery at T7. Lower thoracic and lumbar cord supplied by one radicular artery (artery of Adamkiewicz 90% T12-L2 takeoff, but varies between T9 & L3). The combination of the variable origin of the feeding vessels, the segmental nature of the blood supply to the anterior spinal artery, and the discontinuous blood supply of the spinal cord by the anterior spinal artery, accounts for the failure to reliably predict the frequency of SCI after surgery on the descending aorta. Cephalad to caudad. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * The blood supply to the motor tracts consists of a single anterior spinal artery that continues from the foramen magnum to the filum terminate and is supplied by 5 to 10 radicular arteries. The anterior spinal artery supplies 75% of the cord including the descending motor tracts. The paucity of arterial supply in the anterior cord produces watershed areas, particularly in the thoracic spine. The anterior circulation supplies neurons and synapses that are more sensitive to hypoperfusion injury (eg, anemia, hypotension, blood vessel compression) than the posterior cord. The posterior spinal arteries provide relatively luxuriant flow to the posterior cord. Each vertebral body supplies the posterior vessels [27]. In the intracranial circulation, blood flow through the lenticulostriate vessels from the middle cerebral artery into the internal capsule again creates a watershed area making motor function more vulnerable to hypoperfusion than the ascending sensory tracts. MEP provides unique information about the functional status of the anterior spinal cord and internal capsule [9], [10], [28].It descends to the bottom of the cord and only about 6-7 of the radicular arteries supplies the anterior spinal artery.. Lower thoracic anterior cord has the poorest blood supply � typically one radicular artery at T7. Lower thoracic and lumbar cord supplied by one radicular artery (artery of Adamkiewicz 90% T12-L2 takeoff, but varies between T9 & L3). The combination of the variable origin of the feeding vessels, the segmental nature of the blood supply to the anterior spinal artery, and the discontinuous blood supply of the spinal cord by the anterior spinal artery, accounts for the failure to reliably predict the frequency of SCI after surgery on the descending aorta. Cephalad to caudad. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * The blood supply to the motor tracts consists of a single anterior spinal artery that continues from the foramen magnum to the filum terminate and is supplied by 5 to 10 radicular arteries. The anterior spinal artery supplies 75% of the cord including the descending motor tracts. The paucity of arterial supply in the anterior cord produces watershed areas, particularly in the thoracic spine. The anterior circulation supplies neurons and synapses that are more sensitive to hypoperfusion injury (eg, anemia, hypotension, blood vessel compression) than the posterior cord. The posterior spinal arteries provide relatively luxuriant flow to the posterior cord. Each vertebral body supplies the posterior vessels [27]. In the intracranial circulation, blood flow through the lenticulostriate vessels from the middle cerebral artery into the internal capsule again creates a watershed area making motor function more vulnerable to hypoperfusion than the ascending sensory tracts. MEP provides unique information about the functional status of the anterior spinal cord and internal capsule [9], [10], [28].

20. 02/2009 LHSC Anesthesiology 20 Spinal cord vascular supply

21. 02/2009 LHSC Anesthesiology 21 Anterior horn cell Anterior horn cell is the most sensitive structure in the cord to ischemia Axons (white matter) are relatively resistant to ischemia

22. 02/2009 LHSC Anesthesiology 22 Scoliosis etiology Idiopathic Neuromuscular (flaccidity, spasticity, dyskinesis) Neuropathic Upper motor neuron C.P., spinocerebellar deg., springomyelia, tumour, trauma Lower motor neuron Polio, trauma, spinal muscle atrophy, dysautonomia Myopathic Arthrogryphosis, muscle and myotonic dystrophy, cong. hypotonia, fibre type disproportion

23. 02/2009 LHSC Anesthesiology 23 Scoliosis etiology Congenital 20% have congenital GU malformations;10-15% have congenital heart disease; high association with spinal dysraphism Syndromes Neurofibromatosis Marfan syndrome Compensatory Leg-length discrepancy

24. 02/2009 LHSC Anesthesiology 24 Mechanisms of injury Ischemia, disruption, compression, concussion or distraction Distraction or compression affects region Extent of damage determined by- type, intensity, location and duration of insult Recovery depends on interval of time and reversal of precipitating events.

25. 02/2009 LHSC Anesthesiology 25 Stagnara wakeup test Stagnara wakeup � Clin Orthop 1973 Gold standard Difficulties Unsuitable patients Not able to provide ongoing monitoring Limited repetition capabilities Air embolism Extubation Recall Describe Stagnara test. Describe Stagnara test.

26. 02/2009 LHSC Anesthesiology 26 Clonus test Motor response to stretch reflex Clonus to rapid dorsiflexion of ankle Normal CNS prevents clonus by sending inhibitory potentials to that reflex area in the spinal cord Recovering from GA depresses central inhibition and allows clonus Problems � timing is everything! The ankle clonus test is not a clinically useful measure of spinal cord integrity in children. Ewen A - Can J Anaesth - 01-MAY-2005; 52(5): 524-9 Purpose: Bilateral flexion-induced ankle clonus has been proposed as a test of spinal cord integrity during anesthesia for scoliosis surgery. The purpose of this study was to establish the reliability of this test in normal children emerging from volatile anesthesia. A secondary objective was to determine if there was a difference in the validity of this test with either sevoflurane or isoflurane anesthesia. Methods: In a randomized, prospective blinded clinical trial, 32 healthy children aged three to 13 yr, were randomized to receive either isoflurane (Group I, n = 15) or sevoflurane (Group S, n = 17) for maintenance of anesthesia during dental restorative surgery. During emergence, an observer, blinded to group allocation, recorded ankle clonus scores (number of beats to a maximum of 5 on each side) at 60-sec intervals until tracheal extubation. End-tidal anesthetic concentration was measured contemporaneously. Results: Non-sustained ankle clonus was elicited in a majority of children during emergence: 13 (87%) patients in Group I and 15 (88%) in Group S demonstrated at least non-sustained or unilateral clonus. However, bilateral sustained (> 5 beats�min�1) ankle clonus occurred in only four (27%) patients in Group I and four (24%) patients in Group S (P = 0.83). Conclusion: We conclude that the specificity of the ankle clonus test is too low to be clinically useful as a measure of spinal cord integrity in children, both when isoflurane and sevoflurane are used as the primary anesthetic agent. The ankle clonus test is not a clinically useful measure of spinal cord integrity in children. Ewen A - Can J Anaesth - 01-MAY-2005; 52(5): 524-9 Purpose: Bilateral flexion-induced ankle clonus has been proposed as a test of spinal cord integrity during anesthesia for scoliosis surgery. The purpose of this study was to establish the reliability of this test in normal children emerging from volatile anesthesia. A secondary objective was to determine if there was a difference in the validity of this test with either sevoflurane or isoflurane anesthesia. Methods: In a randomized, prospective blinded clinical trial, 32 healthy children aged three to 13 yr, were randomized to receive either isoflurane (Group I, n = 15) or sevoflurane (Group S, n = 17) for maintenance of anesthesia during dental restorative surgery. During emergence, an observer, blinded to group allocation, recorded ankle clonus scores (number of beats to a maximum of 5 on each side) at 60-sec intervals until tracheal extubation. End-tidal anesthetic concentration was measured contemporaneously. Results: Non-sustained ankle clonus was elicited in a majority of children during emergence: 13 (87%) patients in Group I and 15 (88%) in Group S demonstrated at least non-sustained or unilateral clonus. However, bilateral sustained (> 5 beats�min�1) ankle clonus occurred in only four (27%) patients in Group I and four (24%) patients in Group S (P = 0.83). Conclusion: We conclude that the specificity of the ankle clonus test is too low to be clinically useful as a measure of spinal cord integrity in children, both when isoflurane and sevoflurane are used as the primary anesthetic agent.

27. 02/2009 LHSC Anesthesiology 27 Clonus test The ankle clonus test is not a clinically useful measure of spinal cord integrity in children. Ewen A - Can J Anaesth - 01-MAY-2005; 52(5): 524-9 Conclusion: We conclude that the specificity of the ankle clonus test is too low to be clinically useful as a measure of spinal cord integrity in children, both when isoflurane and sevoflurane are used as the primary anesthetic agent. Ewen A - Can J Anaesth - 01-MAY-2005; 52(5): 524-9 Purpose: Bilateral flexion-induced ankle clonus has been proposed as a test of spinal cord integrity during anesthesia for scoliosis surgery. The purpose of this study was to establish the reliability of this test in normal children emerging from volatile anesthesia. A secondary objective was to determine if there was a difference in the validity of this test with either sevoflurane or isoflurane anesthesia. Methods: In a randomized, prospective blinded clinical trial, 32 healthy children aged three to 13 yr, were randomized to receive either isoflurane (Group I, n = 15) or sevoflurane (Group S, n = 17) for maintenance of anesthesia during dental restorative surgery. During emergence, an observer, blinded to group allocation, recorded ankle clonus scores (number of beats to a maximum of 5 on each side) at 60-sec intervals until tracheal extubation. End-tidal anesthetic concentration was measured contemporaneously. Results: Non-sustained ankle clonus was elicited in a majority of children during emergence: 13 (87%) patients in Group I and 15 (88%) in Group S demonstrated at least non-sustained or unilateral clonus. However, bilateral sustained (> 5 beats�min�1) ankle clonus occurred in only four (27%) patients in Group I and four (24%) patients in Group S (P = 0.83). Conclusion: We conclude that the specificity of the ankle clonus test is too low to be clinically useful as a measure of spinal cord integrity in children, both when isoflurane and sevoflurane are used as the primary anesthetic agent. Ewen A - Can J Anaesth - 01-MAY-2005; 52(5): 524-9 Purpose: Bilateral flexion-induced ankle clonus has been proposed as a test of spinal cord integrity during anesthesia for scoliosis surgery. The purpose of this study was to establish the reliability of this test in normal children emerging from volatile anesthesia. A secondary objective was to determine if there was a difference in the validity of this test with either sevoflurane or isoflurane anesthesia. Methods: In a randomized, prospective blinded clinical trial, 32 healthy children aged three to 13 yr, were randomized to receive either isoflurane (Group I, n = 15) or sevoflurane (Group S, n = 17) for maintenance of anesthesia during dental restorative surgery. During emergence, an observer, blinded to group allocation, recorded ankle clonus scores (number of beats to a maximum of 5 on each side) at 60-sec intervals until tracheal extubation. End-tidal anesthetic concentration was measured contemporaneously. Results: Non-sustained ankle clonus was elicited in a majority of children during emergence: 13 (87%) patients in Group I and 15 (88%) in Group S demonstrated at least non-sustained or unilateral clonus. However, bilateral sustained (> 5 beats�min�1) ankle clonus occurred in only four (27%) patients in Group I and four (24%) patients in Group S (P = 0.83). Conclusion: We conclude that the specificity of the ankle clonus test is too low to be clinically useful as a measure of spinal cord integrity in children, both when isoflurane and sevoflurane are used as the primary anesthetic agent.

28. 02/2009 LHSC Anesthesiology 28 SomatoSensory Evoked Potentials History Time locked neural patterns vs EEG Comparison of electrical potentials: EKG: 1000�V EEG: 10-100�V SSEP: 0.1-10 �V History Sensory evoked potentials were identified as early as 1875. Signal averaging defined in 1950�s but remained a research laboratory tool until the 1970�s when computer technology developed sufficiently to this monitoring into the OR�s. History Sensory evoked potentials were identified as early as 1875. Signal averaging defined in 1950�s but remained a research laboratory tool until the 1970�s when computer technology developed sufficiently to this monitoring into the OR�s.

29. 02/2009 LHSC Anesthesiology 29 Homunculus

30. 02/2009 LHSC Anesthesiology 30 International 10-20 markings

31. 02/2009 LHSC Anesthesiology 31 International 10-20 markings Electrodes are placed either 10% or 20% of the distance between landmarks on the skull. Sagittal - a.of or pertaining to the suture between the parietal bones at the roof of the skull or to a venous canal within the skull and parallel to this suture. b.(in direction or location) from front to back in the median plane or in a plane parallel to the median. Coronal - A coronal plane through the body is a vertical plane from head to foot and parallel to the shoulders Electrodes are placed either 10% or 20% of the distance between landmarks on the skull. Sagittal - a.of or pertaining to the suture between the parietal bones at the roof of the skull or to a venous canal within the skull and parallel to this suture. b.(in direction or location) from front to back in the median plane or in a plane parallel to the median. Coronal - A coronal plane through the body is a vertical plane from head to foot and parallel to the shoulders

32. 02/2009 LHSC Anesthesiology 32 Somatosensory evoked potentials Repetition and averaging Stimulating and recording electrodes Latency and amplitude

33. 02/2009 LHSC Anesthesiology 33 SomatoSensory Evoked Potentials Approximately 100 � 500 stimulus repetitions. Nerve conduction velocity is fairly constant Evoked potentials can be monitored from the periphery to the surface of brain. Stimulation of the peripheral nerve causes a response that ascends the ipsilateral dorsal column, has synapses near the nucleatus cuneatus, decussates near the cervico�medullary junction, ascends by means of the contralateral medial lemniscus, has synapses in the ventroposterolateral nucleus of the thalamus, and finally projects to the contralateral parietal sensory cortex. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD * Stimulation of the peripheral nerve causes a response that ascends the ipsilateral dorsal column, has synapses near the nucleatus cuneatus, decussates near the cervico�medullary junction, ascends by means of the contralateral medial lemniscus, has synapses in the ventroposterolateral nucleus of the thalamus, and finally projects to the contralateral parietal sensory cortex. Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD *

34. 02/2009 LHSC Anesthesiology 34 Somatosensory evoked potentials Negative predictive value � 99.9% Positive predictive value � 42% Factors that can alter traces: Technical Physiologic: temperature, hemoglobin, BP Anesthetic effect on traces: Pentothal, propofol, narcotics and benzodiazepines

35. 02/2009 LHSC Anesthesiology 35 Somatosensory evoked potentials Factors that can alter traces: Anesthetic: inhalational agents and N2O Ketamine and etomidate (familal myoclonic epilepsy) Volatile <= 1 MAC or < 0.5 MAC with nitrous oxide. Peterson et al: Effects of halothane, enflurane, isoflurane and nitrous oxide on somatosensory evoked potentials in humans. Anesthesiology 1986; 65:35-40. Etomidate can increase cortical SSEP by up to 400%. High incidence of myoclonic movements. Familial myoclonic epilepsy patients have abnormally large EP's. TIVA + two IV linesVolatile <= 1 MAC or < 0.5 MAC with nitrous oxide. Peterson et al: Effects of halothane, enflurane, isoflurane and nitrous oxide on somatosensory evoked potentials in humans. Anesthesiology 1986; 65:35-40. Etomidate can increase cortical SSEP by up to 400%. High incidence of myoclonic movements. Familial myoclonic epilepsy patients have abnormally large EP's. TIVA + two IV lines

36. 02/2009 LHSC Anesthesiology 36 Normal UL SSEP�sNormal UL SSEP�s

37. 02/2009 LHSC Anesthesiology 37 Normal LL SSEP�s.Normal LL SSEP�s.

38. 02/2009 LHSC Anesthesiology 38 Loss of UL SSEP due to overextended shoulder. Recovery after repositioning to 90 degrees. Arterial line tracings not affected.Loss of UL SSEP due to overextended shoulder. Recovery after repositioning to 90 degrees. Arterial line tracings not affected.

39. 02/2009 LHSC Anesthesiology 39 Somatosensory evoked potentials Warning � latency increase by 10% Amplitude decrease by 50% Interventions Check equipment, physiology, anesthesia Increase blood pressure, reverse manipulation Limitations Afferent impulses are conducted nonsynaptically. Ten plus minutes needed for SSEP�s to deteriorate. Posterior columns only are monitored

40. 02/2009 LHSC Anesthesiology 40 Motor evoked potentials Electrical or magnetic energy Stimulating sites: Transcranial electrical stimulation (TCES) Neurogenic �motor� evoke potentials Cervical or thoracic spinal cord Nerve root or fibre Free running or triggered EMG

41. 02/2009 LHSC Anesthesiology 41 Motor evoked potentials-TCES Exclusively motor potential Paralysis Specific risk to motor cord Intramedullary tumour Vascular abnormalities Thoraco-abdominal aneurysm Certain spinal corrections

42. 02/2009 LHSC Anesthesiology 42 Motor evoked potentials-TCES Stimulation over pre-central motor strip 3-5 short duration but high voltage pulses Facilitation of cortical neurons Spatial and temporal summation Amplification of myogenic response Not ECT � seizure should not occur Not an ECTNot an ECT

43. 02/2009 LHSC Anesthesiology 43 Motor evoked potentials-TCES Stimulus through the skull to motor cortex. Response can be monitored in epidural space or at the level of muscle. Motorevoked potentials are produced by stimulation of the motor cortex (arrow).The response can be recorded epidurally over the spinal column as a D wave followedby a series of I waves. The pathway synapses in the anterior horn of the spinal cordand the response travel to the muscle by means of the neuromuscular junction (NMJ).The response typically is recorded near the muscle as a compound muscle action potential(CMAP). Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD *Motorevoked potentials are produced by stimulation of the motor cortex (arrow).The response can be recorded epidurally over the spinal column as a D wave followedby a series of I waves. The pathway synapses in the anterior horn of the spinal cordand the response travel to the muscle by means of the neuromuscular junction (NMJ).The response typically is recorded near the muscle as a compound muscle action potential(CMAP). Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD *

44. 02/2009 LHSC Anesthesiology 44 Motor evoked potentials-TCES Recording sites- Epidural: resistant to anesthetic, more consistent Muscle: anterior horn cell, lateralizing information Anesthesia agents Inhalational agents, N2O TIVA drugs Muscle Relaxants Muscle includes anterior horn cell Vascular compromise detected in minutes More sensitive to inhalational agents and nitrous than SSEP Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD Developing standardized criteria for significant tceMEP change has proven difficult because of the large variability in response even in normal awake subjects, a situation that is magnified during general anesthesia. TIVA using propofol or propofol/ketamine mixture plus narcotic usually is used to obtain stable reproducible tceMEP. Exposure to volatile anesthetics significantly reduces amplitude or eliminates tceMEP (Fig.�3) [24], [32], [33]. Benzodiazepines, etomidate, barbiturates, and even high-dose propofol decrease the probability of generating a tceMEP. Only ketamine decreases the threshold for the MEP response [24], [34]. Neuromuscular-blocking drugs must be avoided or their effects very carefully monitored to guarantee EMG change is not caused by neuromuscular blockade. TIVA anesthesia, multiple stimuli, and a stimulus voltage limited to 400V have been reported to produce a tceMEP in 92% of patients. Failures were related to pre-existing neurologic disorders (1.9%) or equipment difficulties Muscle includes anterior horn cell Vascular compromise detected in minutes More sensitive to inhalational agents and nitrous than SSEP Anesthesiology Clinics of North America Volume 24 � Number 4 � December 2006 Monitoring of the Brain and Spinal Cord - Leslie C. Jameson, MD Developing standardized criteria for significant tceMEP change has proven difficult because of the large variability in response even in normal awake subjects, a situation that is magnified during general anesthesia. TIVA using propofol or propofol/ketamine mixture plus narcotic usually is used to obtain stable reproducible tceMEP. Exposure to volatile anesthetics significantly reduces amplitude or eliminates tceMEP (Fig.�3) [24], [32], [33]. Benzodiazepines, etomidate, barbiturates, and even high-dose propofol decrease the probability of generating a tceMEP. Only ketamine decreases the threshold for the MEP response [24], [34]. Neuromuscular-blocking drugs must be avoided or their effects very carefully monitored to guarantee EMG change is not caused by neuromuscular blockade. TIVA anesthesia, multiple stimuli, and a stimulus voltage limited to 400V have been reported to produce a tceMEP in 92% of patients. Failures were related to pre-existing neurologic disorders (1.9%) or equipment difficulties

45. 02/2009 LHSC Anesthesiology 45 Motor evoked potentials-TCES Warning signs � present/absent Risks include: Seizures, skin burns, electrode site infections, patient movement, tongue lacerations and jaw fracture Contraindications: Epilepsy, convexity skull defects, increased ICP, significant cardiac disease, intracranial electrodes, vascular clips, shunts, pacemakers or other biomedical devices ECT Frequency � 80 Hz Pulse duration 0.8-1 msec Duration 3 sec Current 800 mA ECT Frequency � 80 Hz Pulse duration 0.8-1 msec Duration 3 sec Current 800 mA

46. 02/2009 LHSC Anesthesiology 46 Normal TCESNormal TCES

47. 02/2009 LHSC Anesthesiology 47 11 y/o female with neuromuscular scoliosis 15 lb traction on skull and legs TCES disappeared after traction applied. Returned in ten minutes after traction removed. NB get more details of SSEP�s11 y/o female with neuromuscular scoliosis 15 lb traction on skull and legs TCES disappeared after traction applied. Returned in ten minutes after traction removed. NB get more details of SSEP�s

48. 02/2009 LHSC Anesthesiology 48 11 y/o female with neuromuscular scoliosis 15 lb traction on skull and legs TCES disappeared after traction applied. Returned in ten minutes after traction removed. NB get more details of SSEP�s 11 y/o female with neuromuscular scoliosis 15 lb traction on skull and legs TCES disappeared after traction applied. Returned in ten minutes after traction removed. NB get more details of SSEP�s

49. 02/2009 LHSC Anesthesiology 49 Motor evoked potentials-TCES Charles Dong: Ann Thoracic Surgery 74:S1873-6,2002. Intraoperative Spinal Cord Monitoring During Descending Thoracic and Thoracoabdominal Aneurysm Surgery. 16 of 56 showed MEP evidence of spinal cord ischemia while only four of them had delayed associated SSEP changes. 13 had reversal of MEP changes with (a) implantation of more segmental arteries (b) increasing blood flow (c) increase BP or (d) DHCA. None were paraplegic post-op. 3 had no recovery of MEP traces and all awoke paraplegic (SSEP�s relatively preserved) TCES 50�sec 250-100 volts 0.4Hz MEP�s classified as present or absent (no effort to measure amplitude due to significant variability)7 patients: Low distal DBP remedied by increasing distal bypass flow so DBP >60 mm Hg (needed to be increased to >90 mmHg in one patient). 2 patients: loss of MEP�s occurred after 10 minutes of cross clamping resulted in �increased urgency to implant segmental arteries�. (Do the surgeons dilly-dally under normal circumstances??) Shortly after the anastomosis of multiple segmental arteries to the graft, the MEP�s returned. 4 patients: abrupt loss of leg MEP�s after cross clamping suggesting critical segmental arteries were located within the occlude aortic segment. Prompt release of clamps resulted in restoration of MEP�s. Repair under deep hypothermic cardiac arrest (15� C). MEP�s returned after rewarming and no paraplegia on awakening.TCES 50�sec 250-100 volts 0.4Hz MEP�s classified as present or absent (no effort to measure amplitude due to significant variability)7 patients: Low distal DBP remedied by increasing distal bypass flow so DBP >60 mm Hg (needed to be increased to >90 mmHg in one patient). 2 patients: loss of MEP�s occurred after 10 minutes of cross clamping resulted in �increased urgency to implant segmental arteries�. (Do the surgeons dilly-dally under normal circumstances??) Shortly after the anastomosis of multiple segmental arteries to the graft, the MEP�s returned. 4 patients: abrupt loss of leg MEP�s after cross clamping suggesting critical segmental arteries were located within the occlude aortic segment. Prompt release of clamps resulted in restoration of MEP�s. Repair under deep hypothermic cardiac arrest (15� C). MEP�s returned after rewarming and no paraplegia on awakening.

50. 02/2009 LHSC Anesthesiology 50 Motor evoked potentials- EMG Monitor individual nerve roots Electrodes are placed in muscle at risk Quadriceps femoris: L2-L4 Anterior tibialis: L4-L5 Biceps femoris: L5-S1 Gastrocnemius: S1-S2 Patients are not (or partially) paralysed

51. 02/2009 LHSC Anesthesiology 51 Motor evoked potentials- EMG Free running EMG is based on irritated or injured nerves having neural discharges Burst activity suggesting transient irritation Sustained or train activity suggesting more significant injury

52. 02/2009 LHSC Anesthesiology 52 Motor evoked potentials- EMG Triggered EMG can determine proximity to a nerve root Electrical is applied to a pedicle screw or probe. Intact pedicle wall provides a barrier to transmission. EMG activity at less than 4 mA suggests direct contact with the nerve root.

53. 02/2009 LHSC Anesthesiology 53 Neuromonitoring in the Operating Room Define neuromonitoring Risk of CNS damage Spinal cord anatomy Mechanisms of injury Stagnara and Clonus testing Somatosensory evoked potentials Motor evoked potentials