SEP Monitoring. Outline. Outline 1/22/2015. Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring

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SEP Monitoring Andres A Gonzalez, MD Director, Surgical Neurophysiology Keck Medical Center of USC University of Southern California Outline Development of SEPs Stimulation and

1 SEP Monitoring Andres A Gonzalez, MD Director, Surgical Neurophysiology Keck Medical Center of USC University of Southern California Outline Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring Outline Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring 1

ORIGINS OF EVOKED POTENTIALS 1947 Dawson was the first to described changes in the electrical potentials in response to stimulation of peripheral

D.: Cerebral Responses to Electrical Stimulation of Peripheral Nerve in Man. J. Neurol., Neurosurg. and Psychiat., 10: 137-140, 1947.

Stagnaraet al Wake up test in 124 patients Goal: discontinue general anesthesia after placement of hardware and asses neurological function

; and JOUVINROUX, P.: Functional Monitoring of Spinal Cord Activity During Spinal Surgery. Clin. Orthop., 93:173-178, 1973.

2 ORIGINS OF EVOKED POTENTIALS 1947 Dawson was the first to described changes in the electrical potentials in response to stimulation of peripheral nerves 1969 Donaghyand Numotowas probably first one to discuss the prognosis significance of SSEPs in animal following spinal cord injury. Dawson, G. D.: Cerebral Responses to Electrical Stimulation of Peripheral Nerve in Man. J. Neurol., Neurosurg. and Psychiat., 10: , Early Monitoring Prior to the use of EPs the technique used to to functionally monitor the nervous system during done spinal cord procedure was Stagnaraet al Wake up test in 124 patients Goal: discontinue general anesthesia after placement of hardware and asses neurological function Advantages: simple, easy to undo procedure if problems detected Disadvantages: cooperative patient, one time assessment VAUZELLE, C.; STAGNARA, P.; and JOUVINROUX, P.: Functional Monitoring of Spinal Cord Activity During Spinal Surgery. Clin. Orthop., 93: , Somatosensor y 1973 D`Angelo studies (in cats) demonstrated that SSEPs corresponded to ipsilateral posterior column. Also, the severity of SEP changes correlated with the severity of spinal cord damage 2

3 SEP monitoring Introduced in the early 1980 s Early report successful monitoring in 50-80% of cases However, with improved training, anesthetic protocols and equipment resulted in more reliable monitoring Advantages of SSEP monitoring No need to wake up the patient Patient cooperation not required Provides continuous assessment of cord function Outline Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring 3

4 SEP modalities UPPER Median Nerve (C6,7,8, T1) Surgeries above C6 Ulnar Nerve (C8, T1) Sxabove C8 LOWER Posterior tibial (L4,5,S1,2) Peroneal (L4,5,S1) only when PT unavailable Stimulation parameters Constant current stimulator Monophasic square wave current μs Intensity ma Cathode: proximal between the PL-FCR Anode: 2-3 cm distal Stimulation rate: 2-8/sec (avoid multiple of 60) Recording potentials An Evoked Potential is an electrical response to sensory stimulation: vision (VEPs), sensation (SSEP), hearing (BAERs). Size of signals: amplitudes of EP are small Motor NC:> 4000 μv Sensory NC: > 15 μv (or > 6 for sural) EEG: PDR: μv VEPs: ~ 10 μv (photic driving response) SSEPs: 0.8 μv BAERs: 0.2 μv times small 4

5 Recording Parameters Number of repetitions: (SNR) Analysis time: 50 ms (uppers), 100 ms (lowers) Filters: 30-1 khz Montages Typical Upper Limb Montage CPc-FPz = scalp channel (N20, N18, P14) CPc-CPi = scalp channel (isolated N20) CPi-EPc = scalp-non-cephalic channel (N18, P14) C5s-Epc = the cervical channel (N13 ) EPi-EPc = the erb point channel (N9) Localization of SEP Waveforms 5

scalp non cephalic channel (P31, N34) T12 IC = lumbar channel (N22)

6 1/22/2015 Typical montage. CPi FPz = coronal scalp channel (P37) better. CPi (rather than CPc dipole. CPz FPz = midline scalp channel (P37) FPz C5sp= cervical channel or scalp non cephalic channel (P31, N34) T12 IC = lumbar channel (N22) LP PF K = popliteal fossa (N8) Location of Lower Extremity SEP Comparison Arm Leg Cortical N20 P37 Thalamus N18 N34 Posterior column Distal N13 N22 (LP) N9 (EP) N8 (pop) 6

7 SEP Montage SEP Montage Channel Considerations Multiple channels for lower extremity P37-N45 recommended 7

Channel Considerations If C5Sp-FPz channel is used, a collection of N13, inverted P14 are consolidated into one larger waveform Channel Considerations Usefulness of two peripheral potentials:

8 Channel Considerations If C5Sp-FPz channel is used, a collection of N13, inverted P14 are consolidated into one larger waveform Channel Considerations Usefulness of two peripheral potentials: ERBspoint (EP) Popliteal Fossa(PF) potential Channel Considerations ERBspoint intact, loss of subcortical and cortical channels= spinal cord dysfunction Loss of ERBs, subcortical and cortical= limb malposition Loss cortical, preserved subcortical= cerebral ischemia Loss cortical bilateral, preserved subcortical= anesthetic effect 8

9 Outline Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring Intraoperative Neurophysiological Monitoring Electrophysiological testing during operations in which portions of the nervous system are specifically at risk in order to minimize the probability of neurological damage Clinical Efficacy of SSEP Based on a study by Nuweret al. in 1995 Survey of spine surgeons and neurophysiologists regarding 51,263 spine surgeries performed Sensitivity of 92% Specificity of 98.9% High negative predictive value (99.93%), and low positive predictive value (42%) Can reduce major neurologic deficit by 60% M.R. Nuwer et al. / Electroencephalography and clinical Neurophysiology 96 (1995)

10 50/10 Criteria 50% drop in amplitude 10 % increase in latency Caveats on reading the literature False positive caveat: IOM changeswakes up no deficits. In literature is considered a false positive ( instead, should be true positive?) Caveats on reading the literature False positive caveat: IOM changeswakes up no deficits. In literature is considered a false positive ( instead, should be true positive) False negative caveat: No SSEPs changes wake up paralyzed. Is really not a failure of the test. 10

11 SSEPs alone Nevertheless, at a practical level SSEP monitoring is an acceptable indicator of overall spinal cord function Supported by sensitivity % to detect postoperative neurological deficits 2004 Wiedemayer H. J Neurol Neurosurg Psych SSEP only Wiedemayer, H. et al, 2004 Overall Predictive Value SSEP Sensitivity Specificity Reference Scoliosis % 98.90%Nuwer, M.R. et al., clinical neurophysiology, 96(1), pp Carotid Endarterectomy 52% 99%Florence, G., Clinical neurophysiology, 34(1), pp Intracranial and Spinal Tumors 79% 96%Wiedemayer, H. et al., Journal of neurology, neurosurgery, and psychiatry, 75(2), pp Skull Base 58% 100%Bejjani, G.K. et al., Neurosurgery, 43(3), pp discussion Cervical Spine 52% 100%Kelleher, M.O. et al., Spine, 8(3), pp Lumbar Spine 28% 98%Gunnarsson, T. et al., Spine, 29(6), p.677. Tethered Cord 50% 100%Paradiso, G. et al., Spine, 31(18), pp Gonzalez et al. SEP Monitoring. In Husain 2015 andresgo@usc.edu 11

SSEPs alone In addition, reports of false negative outcomes when using SSEP alone illustrated the need for multimodal monitoring Other Modalities Numerous monitoring methods are now available

12 SSEPs alone In addition, reports of false negative outcomes when using SSEP alone illustrated the need for multimodal monitoring Other Modalities Numerous monitoring methods are now available including Motor Evoked Potentials (MEPs) Continuous free running EMG (femg) Evoked or triggered EMG (temg) Other (epidural, mapping, etc) None of this test individually provide global function, but in combination Combined Value of SEP Gonzalez et al. Neurosurgical focus

13 SEP SEP has been the primary spinal cord monitoring modality for decades Serves as a surrogate marker for global spinal cord function It has been complemented by the introduction of MEP, free run and trigger EMG. Advantages of SEP monitoring Has a definable amplitude or latency criteria The signals are reasonably stable Can be continuous Multiple recording sites allow anatomical precision of injury Is capable of recording from peripheral to central somatosensory pathways Outline Development of SEPs Stimulation and recording techniques Predictive value of SEP Uses of SEP monitoring 13

Utility of SEP monitoring Given that SEPsaffect all levels of the

neuromonitoring configurations Hemispheric Deep brain surgeries

Spinal nerve root surgeries Peripheral nerve surgeries Anterior

14 Utility of SEP monitoring Given that SEPsaffect all levels of the neuroaxis it is no surprise that SEP are the staple of most neuromonitoring configurations Hemispheric Deep brain surgeries Posterior fossa surgery Cervical or thoracic spinal surgeries Spinal nerve root surgeries Peripheral nerve surgeries Anterior Lumbar Interbody Fusion (ALIF) Significant changes see in left lower extremity SSEP ALIF 14

ALIF According to Salvador et l, 57% of patients undergoing ALIF at the L4 L5 level are subject to compression of the iliac vessel and oxygen desaturation Vascular Compromise correlated with changes

15 ALIF According to Salvador et l, 57% of patients undergoing ALIF at the L4 L5 level are subject to compression of the iliac vessel and oxygen desaturation Vascular Compromise correlated with changes in the lower extremity SSEP These changes are usually transient and resolve with removal or replacement of the retractor If SSEP recovery is not seen, need to rule out thrombosis Salvador et al. 2003, The Spine Journal Risk of Neurological Deficit Scoliosis surgery % Surgical decompression for spinal tumors 20% Descending thoracic aorta ~40% 2009 ACNS Guidelines 11B Abdominal Aortic Aneurysm Repair with Loss of Lower Extremity SSEP 15

16 1/22/2015 Central Sulcus Localization SSEPs can be recorded directly from the cortical surface A recorded N20 response can be seen in the somatosensory cortex and a P20/P22 response recorded over the motor cortex The place in between where a change in polarity is seen is considered the central sulcus Central Sulcus Localization Positivity up. Loftus CM, 1994 Central Sulcus Localization 1/22/

to the cortex Use of SEPs has not diminished even with the advent of other modalities

17 Central sulcus localization Gugino, Gonzalez et al, 2001 Conclusions Are vital to IOM SSEPsare a reliable way to monitor the somatosensory pathway from the peripheral nerve up to the cortex Use of SEPs has not diminished even with the advent of other modalities (MEPs) Can be used in a wide variety of surgeries, including central sulcus localization 1/22/

SEP Monitoring. Andres A Gonzalez, MD Director, Surgical Neurophysiology Keck Medical Center of USC University of Southern California

SEP Monitoring. Andres A Gonzalez, MD Director, Surgical Neurophysiology Keck Medical Center of USC University of Southern California SEP Monitoring Andres A Gonzalez, MD Director, Surgical Neurophysiology Keck Medical Center of USC University of Southern California Outline Development of SEPs Stimulation and recording techniques Predictive