SlideShare a Scribd company logo
1 of 36
Somatosensory evoked
potentials
BY AHMED ABD EL HADY
Definition
“E.Ps. are the measurement of the electrical potentials produced in response
to stimulating the nervous system (evoked) by sensory, electrical, magnetic
or cognitive stimulation”
Evoked potentials are used to detect conduction disturbances in the central
nervous system.
Evoked responses used for determining:
1- prognosis for severely brain-damaged patients
2-assessment of demyelinating diseases.
Classification
Classification of evoked potentials
Sensory EP Motor EP Event related EP
Visual EP Auditory EP Somatosensory EP
Motor evoked potentials
Motor evoked potentials (MEP) are used to test conductivity in
corticospinal pathways by stimulating the cortex from the outside of
the head by transcranial magnetic stimulator or electrical pulses.
This is a sort of «reversed evoked potential», because the evoked
potentials are recorded from muscles.
Event-related potentials
Event-related potentials (ERP) are evoked when a subject performs a task
which involves responding rapidly and correctly to a stimulus.
The change in the electrical activity of the brain is measured
simultaneously for about one second.
The P300 is the most common event-related potential.(ERP) are used to
judge attention and more complex cognitive processes.
Sensory Evoked potentials
EEG is recorded during repetitive natural stimulation (eg. tap on skin
or flash of light)
Sensory EP is a change in EEG resulting from stimulation of a sensory
pathway:
Visual pathway→ VEP
Auditory pathway → ABR
post.column →SSEP
• The somatosensory-evoked potential (SEP) is the response to electrical stimulation of peripheral
nerves. Stimulation of almost any nerve is possible, although the most commonly studied nerves
are:
• Median
• Ulnar
• Peroneal
• Tibia
•Brief electric pulses are delivered to the peripheral nerve with the cathode
proximal to the anode. The stimulus cannot selectively activate sensory nerves,
so a small muscle twitch is seen.
There are no effects of the retrograde motor volley in the motor nerves on central projections of the
sensory fibers.
• Intensity of the stimulus is adjusted to activate low-threshold myelinated nerve fibers,
which in the motor fibers elicits a small twitch of the innervated muscles. The compound
action potential is conducted through the dorsal roots and into the dorsal columns. The
impulses ascend in the dorsal columns to the gracile and cuneate nuclei where the primary
afferent fibers synapse on the second-order neurons. These axons ascend through the
brainstem to the thalamus. Thalamocortical projections are extensive, as are secondary
intracortical associative projections.
• The recording is made from various levels of the nervous system, including:
• Afferent nerve volley
• Spinal cord
• Brain
•
• SEPs are particularly useful for evaluation of function of the spinal cord.
Lesions of the cord may be invisible to routine imaging, including
magnetic resonance imaging and myelography, yet may have
devastating effects on cord function. Transverse myelitis, multiple
sclerosis (MS), and cord infarction are only three of the potential
causes that can be missed on structural studies. Although almost any
nerve can be studied, median and tibial will be discussed here.
Precautions
1- stimulation aiming at sensory not motor
2- prevention of EMG artifact by making the pt. to relax
3- reduce stimulation rate to prevent EMG artifact
4- Prevent ECG artifact
5- reduction of skin-electrode contact impedence
Median SSEP
• Stimulating electrodes are placed over the median nerve at the wrist with the
cathode proximal to the anode. Stimuli are square-wave pulses given at rates
of 4–7/sec.
• Recording electrodes are placed at the following locations:
• Erb’s point on each side (EP)
• Over the second or fifth cervical spine process (C2S or C5S)
• Scalp over the contralateral cortex (CPc) and ipsilateral cortex (CPi)
• Noncephalic electrode (Ref)
Erb’s point is 2–3 cm above the clavicle, just lateral to the attachment
of the sternocleidomastoid muscle. Stimulation at Erb’s point produces
abduction of the arm and flexion of the elbow. The second and fifth spinous
processes are identified by counting up from the seventh, notable by its
prominence at the base of the neck. CPc and CPi are scalp electrodes
halfway between C3 and P3 or C4 and P4, where CPc is contralateral
to the stimulus and CPi is ipsilateral to the stimulus. These electrodes are
over the motor-sensory cortex. EPi is Erb’s point ipsilateral to the stimulus.
The recommended montage is:
• Channel 1: CPc-CPi
• Channel 2: CPi-Ref
• Channel 3: C5S-Ref
• Channel 4: Epi-Ref
• Waveform Identification and Interpretation
• N9 = from the Epi channel (The potential recorded from Erb’s point )
Origin (Afferent volley in plexus )
• P14 = from the neck channel (The neck potentials include N13 and P14, with
the latter used for clinical interpretation)
Origin ( N13------- Dorsal horn neurons P14 --------- Caudal medial lemniscus)
• N20 = from scalp channels (Scalp potentials include N18 and N20, but the latter
is used for clinical interpretation)
origin ( N18--------- Brainstem and thalamus? N20---------- Thalamocortical
radiations )
• Somatosensory-evoked potential normal data
• N9–P14 interval represents the time for conduction between the
brachial plexus and cervical spine.
• P14–N20 interval represents the conduction between the cervical spine
and the brain. This is called the brain conduction time (BCT).
•Interpretation of abnormalities is as follows:
•Delayed N9 with normal N9–P14 and P14–N20 intervals:
Lesion in the somatosensory nerves at or distal to the
brachial plexus.
• Increased N9–P14 interval with normal P14–N20
interval: Lesion between Erb’s point and the lower
medulla.
• Increased P14–N20 with normal N9–P14 interval: Lesion
between the lower medulla and the cerebral cortex.
Methodology
Sites
Upper limb:
Recording: Erb’s point (N9), Cervical spine 7(N11), Cervical spine
2(N13), contralateral scalp overlying area of 1ry sensory cortex
(N20).
Always use the –ve electrode as recording
Ground: Px to stimulation site
Reference: Forehead Fz
Tibial SSEP
• The proximal stimulating electrode (cathode) is placed at the ankle between
the medial malleolus and the Achilles tendon. The anode is placed 3 cm
distal to the cathode. A ground is placed proximal to the stimulus electrodes,
usually on the calf. Stimulus intensity is set so that each stimulus produces a
small amount of plantar flexion of the toes.
• Recording electrodes are placed as follows:
• CPi = Ipsilateral cortex between C3 and P3 or C4 and P4
• CPz = Midline between Cz and Pz
• FPz = Fpz position of the 10–20 electrode system
• C5S = Over the C5 spinous process
• T12S = Over the T12 spinous process
• Ref = Noncephalic reference
• The montage used for routine tibial SEP is as follows:
• Channel 1: CPi-Fpz
• Channel 2: Cpz-Fpz
• Channel 3: Fpz-C5S
• Channel 4: T12S-Ref
• Waveform Identification and Interpretation
• LP: The lumbar potential (LP) is thought to arise from the afferent nerve
volley in the dorsal roots and dorsal root entry zone.
• Origin ( Dorsal roots and entry zone )
• N21 is best recorded at the L4 spinal level, suggesting that this potential
arises from the cauda equina
• N34: precedes P37, but is not used for clinical interpretation. N34 is the main
negative wave in the FPz-C5S derivation and is preceded by a small positive
wave that is not used for interpretation (P31).
Origin ( Brainstem and thalamus? )
• P37: P37 is a positive potential at about 37 ms that is seen from the scalp
channels.
Origin (primary sensory cortex )
• Somatosensory-evoked potential normal data
• The LP–P37 interval is the time from the cauda equina to the brain. This is
called the central conduction time (CCT).
• Interpretation of abnormalities is as follows:
• Interpretation of tibial SEPs parallels interpretation of median SEPs.
• Prolonged LP with normal LP–P37 interval: Peripheral or distal lesion.
Peripheral neuropathy is most likely, but the slowing could be in the
cauda equina.
• Normal LP with prolonged LP–P37 interval: Abnormal conduction
between the cauda equina and the brain. Median SEP is required to localize
the abnormality to the spinal cord. Normal median SEP indicates a lesion
below the mid-cervical cord. Prolonged median SEP indicates a lesion above
the mid-cervical cord. A second lesion below
the cervical cord cannot be ruled out, however, since the P37 latency is
already prolonged by the higher lesion.
• Prolonged LP and prolonged LP—P37 interval: This suggests two
lesions affecting the peripheral nerve and central conduction. A single
lesion of the cauda equina is possible.
Clinical Correlations
• Transverse Myelitis
Transverse myelitis produces slowing of SEPs that depends on the site of
the lesion. Lesion in the lower cervical or thoracic cord increases central
conduction time without having an effect on brain conduction time. With
recovery, the SEPs abnormalities are improved, but may not return to
normal.
• Multiple Sclerosis
SEP is abnormal in most patients with MS, and can be supporting evidence for
a silent lesion or confirmatory for a myelopathy. The most common finding in
MS is an increase in CCT of the tibial SEP with normal peripheral conduction
(LP). This is because the tibial SEP is assessing conduction along the longest
myelinated nerve tract of any of the evoked potentials. BCT of median nerve
SEP is less commonly increased than tibial nerve SEP CCT. A combined
increase in BCT and CCT can be due to tandem lesions, but also can be due
to a single lesion in the cervical cord.
• Peripheral Neuropathy
Peripheral neuropathy slows peripheral conduction (N9 and LP) with normal
BCT and CCT. The N9–P14 interval may be prolonged with lesions affecting
the proximal portions of the nerves, such as Guillain–Barré syndrome (GBS).
GBS may also occasionally prolong CCT, presumably by affecting the afferent
nerve roots of the cauda equina.
• Vitamin B12 Deficiency
Subacute combined degeneration from vitamin B12 deficiency delays or
abolishes the cervical and scalp SEPs. With treatment, the abnormalities
improve, although not completely to normal. This parallels the clinical
course, where there is improvement but also some persistent deficit.
• Spinal Cord Injury
Cord transection abolishes potentials above the lesion, but most lesions
are incomplete, so the defect in the SEP is variable. Lesions affecting
position sense are most likely to alter the SEP. SEP is not perfectly
sensitive so many patients may have undetectable scalp potentials
despite preservation of some cord function
• Brain Death
Brain death is usually evaluated by EEG or blood flow studies, so the SEP is
not typically used as a confirmatory test. In brain death, the scalp potentials
are absent, usually with preservation of cervical potentials.
• Stroke
SEPs are not commonly used for evaluation of stroke, but if performed, will
show attenuation, delay, and often absence of scalp potentials with stimulation
of the limbs of the affected side. Lesions of the motor-sensory cortical regions
are much more likely to produce abnormal SEPs than lesions elsewhere in the
brain. In general, the severity of the stroke deficit correlates with the degree of
abnormality of the SEP, but wide variation is common. SEP may be absent with
subtle deficit and SEP may be preserved with major deficit.
• Other uses
• Monitoring during temporary clipping in aneurysm surgery has shown that a
very prompt loss of cortical SSEP response (less than 1 minute after clipping)
is associated with development of permanent neurologic deficit.
• SSEP in spinal surgeries has become standard care of monitoring.
• Monitoring during carotid endarterectomy. Intraoperative SSEP changes
are used as an indication for shunt placement and to predict postoperative
morbidity.
Somatosensory evoked potential

More Related Content

What's hot

Late Responses (F-wave and H.Reflex)
Late Responses (F-wave and H.Reflex)Late Responses (F-wave and H.Reflex)
Late Responses (F-wave and H.Reflex)Murtaza Syed
 
Nerves conduction study
Nerves conduction study Nerves conduction study
Nerves conduction study Sachin Adukia
 
Repetitive Nerve Stimulation (RNS)
Repetitive Nerve Stimulation (RNS)Repetitive Nerve Stimulation (RNS)
Repetitive Nerve Stimulation (RNS)Murtaza Syed
 
Repetitive nerve stimulation test
Repetitive nerve stimulation test Repetitive nerve stimulation test
Repetitive nerve stimulation test NeurologyKota
 
Somato Sensory Evoked Potentials (SSEP) By: Murtaza Syed
Somato Sensory Evoked Potentials (SSEP) By: Murtaza SyedSomato Sensory Evoked Potentials (SSEP) By: Murtaza Syed
Somato Sensory Evoked Potentials (SSEP) By: Murtaza SyedMurtaza Syed
 
Nerves conduction study
Nerves conduction studyNerves conduction study
Nerves conduction studyAhmad Shahir
 
Somatosensory and motor evoked potentials by neelothpala
Somatosensory and motor evoked potentials by neelothpalaSomatosensory and motor evoked potentials by neelothpala
Somatosensory and motor evoked potentials by neelothpalavrkv2007
 
Sympathetic Skin Response (SSR) Testing
Sympathetic Skin Response (SSR) TestingSympathetic Skin Response (SSR) Testing
Sympathetic Skin Response (SSR) TestingMurtaza Syed
 
Pathophysiology of spasticity
Pathophysiology of spasticityPathophysiology of spasticity
Pathophysiology of spasticityNeurologyKota
 
Overview of Nerve Conduction Study
Overview of Nerve Conduction StudyOverview of Nerve Conduction Study
Overview of Nerve Conduction StudyPramod Krishnan
 
Autonomic nervous system testing
Autonomic nervous system testingAutonomic nervous system testing
Autonomic nervous system testingVaibhaviParmar7
 
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)Upper Extremity Somatosensory Evoked Potential (Upper SSEP)
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)Anurag Tewari MD
 
Evoked Potential ppt.pptx
Evoked Potential ppt.pptxEvoked Potential ppt.pptx
Evoked Potential ppt.pptxAshik Dhakal
 

What's hot (20)

Late Responses (F-wave and H.Reflex)
Late Responses (F-wave and H.Reflex)Late Responses (F-wave and H.Reflex)
Late Responses (F-wave and H.Reflex)
 
Nerves conduction study
Nerves conduction study Nerves conduction study
Nerves conduction study
 
Emg presentation
Emg presentationEmg presentation
Emg presentation
 
Repetitive Nerve Stimulation (RNS)
Repetitive Nerve Stimulation (RNS)Repetitive Nerve Stimulation (RNS)
Repetitive Nerve Stimulation (RNS)
 
Repetitive nerve stimulation test
Repetitive nerve stimulation test Repetitive nerve stimulation test
Repetitive nerve stimulation test
 
Evolked potential
Evolked potentialEvolked potential
Evolked potential
 
repetitive nerve stimulation
repetitive nerve stimulationrepetitive nerve stimulation
repetitive nerve stimulation
 
Interpretation of NCS and EMG
Interpretation of NCS and EMG Interpretation of NCS and EMG
Interpretation of NCS and EMG
 
Somato Sensory Evoked Potentials (SSEP) By: Murtaza Syed
Somato Sensory Evoked Potentials (SSEP) By: Murtaza SyedSomato Sensory Evoked Potentials (SSEP) By: Murtaza Syed
Somato Sensory Evoked Potentials (SSEP) By: Murtaza Syed
 
Nerves conduction study
Nerves conduction studyNerves conduction study
Nerves conduction study
 
Somatosensory and motor evoked potentials by neelothpala
Somatosensory and motor evoked potentials by neelothpalaSomatosensory and motor evoked potentials by neelothpala
Somatosensory and motor evoked potentials by neelothpala
 
Blink reflex
Blink reflex Blink reflex
Blink reflex
 
Sympathetic Skin Response (SSR) Testing
Sympathetic Skin Response (SSR) TestingSympathetic Skin Response (SSR) Testing
Sympathetic Skin Response (SSR) Testing
 
Ssep pathways
Ssep pathwaysSsep pathways
Ssep pathways
 
NCV AND EMG
NCV AND EMGNCV AND EMG
NCV AND EMG
 
Pathophysiology of spasticity
Pathophysiology of spasticityPathophysiology of spasticity
Pathophysiology of spasticity
 
Overview of Nerve Conduction Study
Overview of Nerve Conduction StudyOverview of Nerve Conduction Study
Overview of Nerve Conduction Study
 
Autonomic nervous system testing
Autonomic nervous system testingAutonomic nervous system testing
Autonomic nervous system testing
 
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)Upper Extremity Somatosensory Evoked Potential (Upper SSEP)
Upper Extremity Somatosensory Evoked Potential (Upper SSEP)
 
Evoked Potential ppt.pptx
Evoked Potential ppt.pptxEvoked Potential ppt.pptx
Evoked Potential ppt.pptx
 

Viewers also liked

Repetitive transcanial magnetic stimulation(r tms) for depression treatment
Repetitive transcanial magnetic stimulation(r tms) for depression treatmentRepetitive transcanial magnetic stimulation(r tms) for depression treatment
Repetitive transcanial magnetic stimulation(r tms) for depression treatmentGuru Prasath
 
Issues in brainmapping...The secrets of conventional EEG
Issues in brainmapping...The secrets of conventional EEGIssues in brainmapping...The secrets of conventional EEG
Issues in brainmapping...The secrets of conventional EEGProfessor Yasser Metwally
 
Evoked potentials, clinical importance & physiological basis of consciousness...
Evoked potentials, clinical importance & physiological basis of consciousness...Evoked potentials, clinical importance & physiological basis of consciousness...
Evoked potentials, clinical importance & physiological basis of consciousness...Rajesh Goit
 
Vep and its practical importance
Vep and its practical importanceVep and its practical importance
Vep and its practical importancenikhilzandu
 
Auditory brainstem response (ABR)
Auditory brainstem response (ABR)Auditory brainstem response (ABR)
Auditory brainstem response (ABR)Dr Pankaj Yadav
 
Encoding of frequency and volley theory
Encoding of frequency and volley theoryEncoding of frequency and volley theory
Encoding of frequency and volley theoryKemUnited
 
Eeg normal inglish
Eeg normal inglishEeg normal inglish
Eeg normal inglishguestf282ad
 
Hidden context tree modeling of EEG data
Hidden context tree modeling of EEG dataHidden context tree modeling of EEG data
Hidden context tree modeling of EEG dataNeuroMat
 
Melior neurophysiology models 13 mar13
Melior neurophysiology models 13 mar13Melior neurophysiology models 13 mar13
Melior neurophysiology models 13 mar13John Gruner
 
Electrophysiological tests
Electrophysiological testsElectrophysiological tests
Electrophysiological testsReshma Peter
 
General Principles Part 1 Historical And Classifications
General Principles Part 1 Historical And ClassificationsGeneral Principles Part 1 Historical And Classifications
General Principles Part 1 Historical And ClassificationsBrent Rasmussen
 
Long latency responses (Niraj)
Long latency responses (Niraj)Long latency responses (Niraj)
Long latency responses (Niraj)Niraj Kumar
 

Viewers also liked (20)

Chapter 7
Chapter 7Chapter 7
Chapter 7
 
Repetitive transcanial magnetic stimulation(r tms) for depression treatment
Repetitive transcanial magnetic stimulation(r tms) for depression treatmentRepetitive transcanial magnetic stimulation(r tms) for depression treatment
Repetitive transcanial magnetic stimulation(r tms) for depression treatment
 
Issues in brainmapping...The secrets of conventional EEG
Issues in brainmapping...The secrets of conventional EEGIssues in brainmapping...The secrets of conventional EEG
Issues in brainmapping...The secrets of conventional EEG
 
Evoked potentials, clinical importance & physiological basis of consciousness...
Evoked potentials, clinical importance & physiological basis of consciousness...Evoked potentials, clinical importance & physiological basis of consciousness...
Evoked potentials, clinical importance & physiological basis of consciousness...
 
Vep and its practical importance
Vep and its practical importanceVep and its practical importance
Vep and its practical importance
 
Eeg basics.drjma
Eeg basics.drjmaEeg basics.drjma
Eeg basics.drjma
 
EEG artifacts
EEG artifactsEEG artifacts
EEG artifacts
 
EEG: Basics
EEG: BasicsEEG: Basics
EEG: Basics
 
Auditory brainstem response (ABR)
Auditory brainstem response (ABR)Auditory brainstem response (ABR)
Auditory brainstem response (ABR)
 
Long-Latency Motor Evoked Potentials in Spinal Cord Injury
Long-Latency Motor Evoked Potentials in Spinal Cord InjuryLong-Latency Motor Evoked Potentials in Spinal Cord Injury
Long-Latency Motor Evoked Potentials in Spinal Cord Injury
 
Encoding of frequency and volley theory
Encoding of frequency and volley theoryEncoding of frequency and volley theory
Encoding of frequency and volley theory
 
Chapter6
Chapter6Chapter6
Chapter6
 
Eeg normal inglish
Eeg normal inglishEeg normal inglish
Eeg normal inglish
 
Development of nervous system
Development of nervous systemDevelopment of nervous system
Development of nervous system
 
Hidden context tree modeling of EEG data
Hidden context tree modeling of EEG dataHidden context tree modeling of EEG data
Hidden context tree modeling of EEG data
 
Melior neurophysiology models 13 mar13
Melior neurophysiology models 13 mar13Melior neurophysiology models 13 mar13
Melior neurophysiology models 13 mar13
 
Electrophysiological tests
Electrophysiological testsElectrophysiological tests
Electrophysiological tests
 
General Principles Part 1 Historical And Classifications
General Principles Part 1 Historical And ClassificationsGeneral Principles Part 1 Historical And Classifications
General Principles Part 1 Historical And Classifications
 
Anatomy of limbic system
Anatomy of  limbic  systemAnatomy of  limbic  system
Anatomy of limbic system
 
Long latency responses (Niraj)
Long latency responses (Niraj)Long latency responses (Niraj)
Long latency responses (Niraj)
 

Similar to Somatosensory evoked potential

Intraoperative Evoked Potential Monitoring
Intraoperative Evoked Potential MonitoringIntraoperative Evoked Potential Monitoring
Intraoperative Evoked Potential MonitoringPramod Krishnan
 
Evoked potentials.pptx
Evoked potentials.pptxEvoked potentials.pptx
Evoked potentials.pptxPreet Mehta
 
Intraoperative Neurophysiological Monitoring Brain
Intraoperative Neurophysiological Monitoring BrainIntraoperative Neurophysiological Monitoring Brain
Intraoperative Neurophysiological Monitoring BrainFarrukh Javeed
 
Fundamentals of Nerve conduction studies and its Interpretations
Fundamentals of Nerve conduction studies and its InterpretationsFundamentals of Nerve conduction studies and its Interpretations
Fundamentals of Nerve conduction studies and its InterpretationsDr.suresh kumar MPT(Neuro)PhD
 
Nerve conduction study
Nerve conduction studyNerve conduction study
Nerve conduction studyGaraka Rabel
 
Advances in neuro anesthesia monitoring
Advances in neuro anesthesia monitoringAdvances in neuro anesthesia monitoring
Advances in neuro anesthesia monitoringWesam Mousa
 
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHY
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHYNERVE CONDUCTION STUDIES, ELECTROMYOGRAPHY
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHYPGIMER,DR.RML HOSPITAL
 
Intra operative neurophysiological monitoring
Intra operative neurophysiological monitoringIntra operative neurophysiological monitoring
Intra operative neurophysiological monitoringKode Sashanka
 
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)Lower Extremity Somatosensory Evoked Potentials (lower SSEP)
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)Anurag Tewari MD
 
13- Electrodiagnosis in pedriatrics (DPT-9).pptx
13- Electrodiagnosis in pedriatrics (DPT-9).pptx13- Electrodiagnosis in pedriatrics (DPT-9).pptx
13- Electrodiagnosis in pedriatrics (DPT-9).pptxcutefairy5
 
Radial nerve palsy
Radial nerve palsyRadial nerve palsy
Radial nerve palsymanoj das
 
Eeg with image - Medical Electronics - Hints for Slow Learner
Eeg with image - Medical Electronics - Hints for Slow LearnerEeg with image - Medical Electronics - Hints for Slow Learner
Eeg with image - Medical Electronics - Hints for Slow LearnerMathavan N
 
Interpretation of NCV.pptx
Interpretation of NCV.pptxInterpretation of NCV.pptx
Interpretation of NCV.pptxKetakiPatani1
 
The+Nervous+System
The+Nervous+SystemThe+Nervous+System
The+Nervous+Systemahsapbiology
 

Similar to Somatosensory evoked potential (20)

Intraoperative Evoked Potential Monitoring
Intraoperative Evoked Potential MonitoringIntraoperative Evoked Potential Monitoring
Intraoperative Evoked Potential Monitoring
 
Evoked potentials.pptx
Evoked potentials.pptxEvoked potentials.pptx
Evoked potentials.pptx
 
Intraoperative Neurophysiological Monitoring Brain
Intraoperative Neurophysiological Monitoring BrainIntraoperative Neurophysiological Monitoring Brain
Intraoperative Neurophysiological Monitoring Brain
 
SSEP BY FZ.pptx
SSEP BY FZ.pptxSSEP BY FZ.pptx
SSEP BY FZ.pptx
 
Fundamentals of Nerve conduction studies and its Interpretations
Fundamentals of Nerve conduction studies and its InterpretationsFundamentals of Nerve conduction studies and its Interpretations
Fundamentals of Nerve conduction studies and its Interpretations
 
EEG Generators
EEG GeneratorsEEG Generators
EEG Generators
 
Eeg
EegEeg
Eeg
 
Nerve conduction study
Nerve conduction studyNerve conduction study
Nerve conduction study
 
Advances in neuro anesthesia monitoring
Advances in neuro anesthesia monitoringAdvances in neuro anesthesia monitoring
Advances in neuro anesthesia monitoring
 
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHY
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHYNERVE CONDUCTION STUDIES, ELECTROMYOGRAPHY
NERVE CONDUCTION STUDIES, ELECTROMYOGRAPHY
 
Trigeminovascular system seminar
Trigeminovascular system seminarTrigeminovascular system seminar
Trigeminovascular system seminar
 
Intra operative neurophysiological monitoring
Intra operative neurophysiological monitoringIntra operative neurophysiological monitoring
Intra operative neurophysiological monitoring
 
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)Lower Extremity Somatosensory Evoked Potentials (lower SSEP)
Lower Extremity Somatosensory Evoked Potentials (lower SSEP)
 
13- Electrodiagnosis in pedriatrics (DPT-9).pptx
13- Electrodiagnosis in pedriatrics (DPT-9).pptx13- Electrodiagnosis in pedriatrics (DPT-9).pptx
13- Electrodiagnosis in pedriatrics (DPT-9).pptx
 
Radial nerve palsy
Radial nerve palsyRadial nerve palsy
Radial nerve palsy
 
Eeg with image - Medical Electronics - Hints for Slow Learner
Eeg with image - Medical Electronics - Hints for Slow LearnerEeg with image - Medical Electronics - Hints for Slow Learner
Eeg with image - Medical Electronics - Hints for Slow Learner
 
Lecture 2 d instrumentation used in the measurement of acoustic signals and a...
Lecture 2 d instrumentation used in the measurement of acoustic signals and a...Lecture 2 d instrumentation used in the measurement of acoustic signals and a...
Lecture 2 d instrumentation used in the measurement of acoustic signals and a...
 
Interpretation of NCV.pptx
Interpretation of NCV.pptxInterpretation of NCV.pptx
Interpretation of NCV.pptx
 
Exercise physiology 4
Exercise physiology 4Exercise physiology 4
Exercise physiology 4
 
The+Nervous+System
The+Nervous+SystemThe+Nervous+System
The+Nervous+System
 

Recently uploaded

In-service education (Nursing Mangement)
In-service education (Nursing Mangement)In-service education (Nursing Mangement)
In-service education (Nursing Mangement)Monika Kanwar
 
Effects of vaping e-cigarettes on arterial health
Effects of vaping e-cigarettes on arterial healthEffects of vaping e-cigarettes on arterial health
Effects of vaping e-cigarettes on arterial healthCatherine Liao
 
linearity concept of significance, standard deviation, chi square test, stude...
linearity concept of significance, standard deviation, chi square test, stude...linearity concept of significance, standard deviation, chi square test, stude...
linearity concept of significance, standard deviation, chi square test, stude...KavyasriPuttamreddy
 
Antiplatelets in IHD, Dose Duration, DAPT vs SAPT
Antiplatelets in IHD, Dose Duration, DAPT vs SAPTAntiplatelets in IHD, Dose Duration, DAPT vs SAPT
Antiplatelets in IHD, Dose Duration, DAPT vs SAPTAkashGanganePatil1
 
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)Dr. Aryan (Anish Dhakal)
 
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdf
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdfรายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdf
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdfVorawut Wongumpornpinit
 
Cervical screening – taking care of your health flipchart (Vietnamese)
Cervical screening – taking care of your health flipchart (Vietnamese)Cervical screening – taking care of your health flipchart (Vietnamese)
Cervical screening – taking care of your health flipchart (Vietnamese)Cancer Institute NSW
 
World Hypertension Day 17th may 2024 ppt
World Hypertension Day 17th may 2024 pptWorld Hypertension Day 17th may 2024 ppt
World Hypertension Day 17th may 2024 pptdesktoppc
 
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHY
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHYTUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHY
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHYDRPREETHIJAMESP
 
The Orbit & its contents by Dr. Rabia I. Gandapore.pptx
The Orbit & its contents by Dr. Rabia I. Gandapore.pptxThe Orbit & its contents by Dr. Rabia I. Gandapore.pptx
The Orbit & its contents by Dr. Rabia I. Gandapore.pptxDr. Rabia Inam Gandapore
 
DIGITAL RADIOGRAPHY-SABBU KHATOON .pptx
DIGITAL RADIOGRAPHY-SABBU KHATOON  .pptxDIGITAL RADIOGRAPHY-SABBU KHATOON  .pptx
DIGITAL RADIOGRAPHY-SABBU KHATOON .pptxSabbu Khatoon
 
Circulation through Special Regions -characteristics and regulation
Circulation through Special Regions -characteristics and regulationCirculation through Special Regions -characteristics and regulation
Circulation through Special Regions -characteristics and regulationMedicoseAcademics
 
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDF
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDFNCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDF
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDFShahid Hussain
 
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptx
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptxCURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptx
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptxDr KHALID B.M
 
Creating Accessible Public Health Communications
Creating Accessible Public Health CommunicationsCreating Accessible Public Health Communications
Creating Accessible Public Health Communicationskatiequigley33
 
BMK Glycidic Acid (sodium salt) CAS 5449-12-7 Pharmaceutical intermediates
BMK Glycidic Acid (sodium salt)  CAS 5449-12-7 Pharmaceutical intermediatesBMK Glycidic Acid (sodium salt)  CAS 5449-12-7 Pharmaceutical intermediates
BMK Glycidic Acid (sodium salt) CAS 5449-12-7 Pharmaceutical intermediatesdorademei
 
Scientificity and feasibility study of non-invasive central arterial pressure...
Scientificity and feasibility study of non-invasive central arterial pressure...Scientificity and feasibility study of non-invasive central arterial pressure...
Scientificity and feasibility study of non-invasive central arterial pressure...Catherine Liao
 
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1THORACOTOMY . SURGICAL PERSPECTIVES VOL 1
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1DR SETH JOTHAM
 
Denture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of actionDenture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of actionDr.shiva sai vemula
 
A thorough review of supernormal conduction.pptx
A thorough review of supernormal conduction.pptxA thorough review of supernormal conduction.pptx
A thorough review of supernormal conduction.pptxSergio Pinski
 

Recently uploaded (20)

In-service education (Nursing Mangement)
In-service education (Nursing Mangement)In-service education (Nursing Mangement)
In-service education (Nursing Mangement)
 
Effects of vaping e-cigarettes on arterial health
Effects of vaping e-cigarettes on arterial healthEffects of vaping e-cigarettes on arterial health
Effects of vaping e-cigarettes on arterial health
 
linearity concept of significance, standard deviation, chi square test, stude...
linearity concept of significance, standard deviation, chi square test, stude...linearity concept of significance, standard deviation, chi square test, stude...
linearity concept of significance, standard deviation, chi square test, stude...
 
Antiplatelets in IHD, Dose Duration, DAPT vs SAPT
Antiplatelets in IHD, Dose Duration, DAPT vs SAPTAntiplatelets in IHD, Dose Duration, DAPT vs SAPT
Antiplatelets in IHD, Dose Duration, DAPT vs SAPT
 
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)
Book Trailer: PGMEE in a Nutshell (CEE MD/MS PG Entrance Examination)
 
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdf
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdfรายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdf
รายการตํารับยาแผนไทยแห่งชาติ ฉบับ พ.ศ. 2564.pdf
 
Cervical screening – taking care of your health flipchart (Vietnamese)
Cervical screening – taking care of your health flipchart (Vietnamese)Cervical screening – taking care of your health flipchart (Vietnamese)
Cervical screening – taking care of your health flipchart (Vietnamese)
 
World Hypertension Day 17th may 2024 ppt
World Hypertension Day 17th may 2024 pptWorld Hypertension Day 17th may 2024 ppt
World Hypertension Day 17th may 2024 ppt
 
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHY
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHYTUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHY
TUBERCULINUM-2.BHMS.MATERIA MEDICA.HOMOEOPATHY
 
The Orbit & its contents by Dr. Rabia I. Gandapore.pptx
The Orbit & its contents by Dr. Rabia I. Gandapore.pptxThe Orbit & its contents by Dr. Rabia I. Gandapore.pptx
The Orbit & its contents by Dr. Rabia I. Gandapore.pptx
 
DIGITAL RADIOGRAPHY-SABBU KHATOON .pptx
DIGITAL RADIOGRAPHY-SABBU KHATOON  .pptxDIGITAL RADIOGRAPHY-SABBU KHATOON  .pptx
DIGITAL RADIOGRAPHY-SABBU KHATOON .pptx
 
Circulation through Special Regions -characteristics and regulation
Circulation through Special Regions -characteristics and regulationCirculation through Special Regions -characteristics and regulation
Circulation through Special Regions -characteristics and regulation
 
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDF
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDFNCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDF
NCLEX RN REVIEW EXAM CONTENT BLUE BOOK PDF
 
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptx
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptxCURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptx
CURRENT HEALTH PROBLEMS AND ITS SOLUTION BY AYURVEDA.pptx
 
Creating Accessible Public Health Communications
Creating Accessible Public Health CommunicationsCreating Accessible Public Health Communications
Creating Accessible Public Health Communications
 
BMK Glycidic Acid (sodium salt) CAS 5449-12-7 Pharmaceutical intermediates
BMK Glycidic Acid (sodium salt)  CAS 5449-12-7 Pharmaceutical intermediatesBMK Glycidic Acid (sodium salt)  CAS 5449-12-7 Pharmaceutical intermediates
BMK Glycidic Acid (sodium salt) CAS 5449-12-7 Pharmaceutical intermediates
 
Scientificity and feasibility study of non-invasive central arterial pressure...
Scientificity and feasibility study of non-invasive central arterial pressure...Scientificity and feasibility study of non-invasive central arterial pressure...
Scientificity and feasibility study of non-invasive central arterial pressure...
 
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1THORACOTOMY . SURGICAL PERSPECTIVES VOL 1
THORACOTOMY . SURGICAL PERSPECTIVES VOL 1
 
Denture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of actionDenture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of action
 
A thorough review of supernormal conduction.pptx
A thorough review of supernormal conduction.pptxA thorough review of supernormal conduction.pptx
A thorough review of supernormal conduction.pptx
 

Somatosensory evoked potential

  • 2. Definition “E.Ps. are the measurement of the electrical potentials produced in response to stimulating the nervous system (evoked) by sensory, electrical, magnetic or cognitive stimulation” Evoked potentials are used to detect conduction disturbances in the central nervous system. Evoked responses used for determining: 1- prognosis for severely brain-damaged patients 2-assessment of demyelinating diseases.
  • 3. Classification Classification of evoked potentials Sensory EP Motor EP Event related EP Visual EP Auditory EP Somatosensory EP
  • 4. Motor evoked potentials Motor evoked potentials (MEP) are used to test conductivity in corticospinal pathways by stimulating the cortex from the outside of the head by transcranial magnetic stimulator or electrical pulses. This is a sort of «reversed evoked potential», because the evoked potentials are recorded from muscles.
  • 5. Event-related potentials Event-related potentials (ERP) are evoked when a subject performs a task which involves responding rapidly and correctly to a stimulus. The change in the electrical activity of the brain is measured simultaneously for about one second. The P300 is the most common event-related potential.(ERP) are used to judge attention and more complex cognitive processes.
  • 6. Sensory Evoked potentials EEG is recorded during repetitive natural stimulation (eg. tap on skin or flash of light) Sensory EP is a change in EEG resulting from stimulation of a sensory pathway: Visual pathway→ VEP Auditory pathway → ABR post.column →SSEP
  • 7. • The somatosensory-evoked potential (SEP) is the response to electrical stimulation of peripheral nerves. Stimulation of almost any nerve is possible, although the most commonly studied nerves are: • Median • Ulnar • Peroneal • Tibia •Brief electric pulses are delivered to the peripheral nerve with the cathode proximal to the anode. The stimulus cannot selectively activate sensory nerves, so a small muscle twitch is seen. There are no effects of the retrograde motor volley in the motor nerves on central projections of the sensory fibers.
  • 8. • Intensity of the stimulus is adjusted to activate low-threshold myelinated nerve fibers, which in the motor fibers elicits a small twitch of the innervated muscles. The compound action potential is conducted through the dorsal roots and into the dorsal columns. The impulses ascend in the dorsal columns to the gracile and cuneate nuclei where the primary afferent fibers synapse on the second-order neurons. These axons ascend through the brainstem to the thalamus. Thalamocortical projections are extensive, as are secondary intracortical associative projections. • The recording is made from various levels of the nervous system, including: • Afferent nerve volley • Spinal cord • Brain •
  • 9.
  • 10. • SEPs are particularly useful for evaluation of function of the spinal cord. Lesions of the cord may be invisible to routine imaging, including magnetic resonance imaging and myelography, yet may have devastating effects on cord function. Transverse myelitis, multiple sclerosis (MS), and cord infarction are only three of the potential causes that can be missed on structural studies. Although almost any nerve can be studied, median and tibial will be discussed here.
  • 11. Precautions 1- stimulation aiming at sensory not motor 2- prevention of EMG artifact by making the pt. to relax 3- reduce stimulation rate to prevent EMG artifact 4- Prevent ECG artifact 5- reduction of skin-electrode contact impedence
  • 12. Median SSEP • Stimulating electrodes are placed over the median nerve at the wrist with the cathode proximal to the anode. Stimuli are square-wave pulses given at rates of 4–7/sec. • Recording electrodes are placed at the following locations: • Erb’s point on each side (EP) • Over the second or fifth cervical spine process (C2S or C5S) • Scalp over the contralateral cortex (CPc) and ipsilateral cortex (CPi) • Noncephalic electrode (Ref)
  • 13. Erb’s point is 2–3 cm above the clavicle, just lateral to the attachment of the sternocleidomastoid muscle. Stimulation at Erb’s point produces abduction of the arm and flexion of the elbow. The second and fifth spinous processes are identified by counting up from the seventh, notable by its prominence at the base of the neck. CPc and CPi are scalp electrodes halfway between C3 and P3 or C4 and P4, where CPc is contralateral to the stimulus and CPi is ipsilateral to the stimulus. These electrodes are over the motor-sensory cortex. EPi is Erb’s point ipsilateral to the stimulus. The recommended montage is: • Channel 1: CPc-CPi • Channel 2: CPi-Ref • Channel 3: C5S-Ref • Channel 4: Epi-Ref
  • 14.
  • 15. • Waveform Identification and Interpretation
  • 16. • N9 = from the Epi channel (The potential recorded from Erb’s point ) Origin (Afferent volley in plexus ) • P14 = from the neck channel (The neck potentials include N13 and P14, with the latter used for clinical interpretation) Origin ( N13------- Dorsal horn neurons P14 --------- Caudal medial lemniscus) • N20 = from scalp channels (Scalp potentials include N18 and N20, but the latter is used for clinical interpretation) origin ( N18--------- Brainstem and thalamus? N20---------- Thalamocortical radiations )
  • 17. • Somatosensory-evoked potential normal data • N9–P14 interval represents the time for conduction between the brachial plexus and cervical spine. • P14–N20 interval represents the conduction between the cervical spine and the brain. This is called the brain conduction time (BCT).
  • 18. •Interpretation of abnormalities is as follows: •Delayed N9 with normal N9–P14 and P14–N20 intervals: Lesion in the somatosensory nerves at or distal to the brachial plexus. • Increased N9–P14 interval with normal P14–N20 interval: Lesion between Erb’s point and the lower medulla. • Increased P14–N20 with normal N9–P14 interval: Lesion between the lower medulla and the cerebral cortex.
  • 19. Methodology Sites Upper limb: Recording: Erb’s point (N9), Cervical spine 7(N11), Cervical spine 2(N13), contralateral scalp overlying area of 1ry sensory cortex (N20). Always use the –ve electrode as recording Ground: Px to stimulation site Reference: Forehead Fz
  • 20. Tibial SSEP • The proximal stimulating electrode (cathode) is placed at the ankle between the medial malleolus and the Achilles tendon. The anode is placed 3 cm distal to the cathode. A ground is placed proximal to the stimulus electrodes, usually on the calf. Stimulus intensity is set so that each stimulus produces a small amount of plantar flexion of the toes. • Recording electrodes are placed as follows: • CPi = Ipsilateral cortex between C3 and P3 or C4 and P4 • CPz = Midline between Cz and Pz • FPz = Fpz position of the 10–20 electrode system • C5S = Over the C5 spinous process • T12S = Over the T12 spinous process • Ref = Noncephalic reference
  • 21.
  • 22. • The montage used for routine tibial SEP is as follows: • Channel 1: CPi-Fpz • Channel 2: Cpz-Fpz • Channel 3: Fpz-C5S • Channel 4: T12S-Ref
  • 23. • Waveform Identification and Interpretation
  • 24. • LP: The lumbar potential (LP) is thought to arise from the afferent nerve volley in the dorsal roots and dorsal root entry zone. • Origin ( Dorsal roots and entry zone ) • N21 is best recorded at the L4 spinal level, suggesting that this potential arises from the cauda equina • N34: precedes P37, but is not used for clinical interpretation. N34 is the main negative wave in the FPz-C5S derivation and is preceded by a small positive wave that is not used for interpretation (P31). Origin ( Brainstem and thalamus? ) • P37: P37 is a positive potential at about 37 ms that is seen from the scalp channels. Origin (primary sensory cortex )
  • 25. • Somatosensory-evoked potential normal data • The LP–P37 interval is the time from the cauda equina to the brain. This is called the central conduction time (CCT).
  • 26. • Interpretation of abnormalities is as follows: • Interpretation of tibial SEPs parallels interpretation of median SEPs. • Prolonged LP with normal LP–P37 interval: Peripheral or distal lesion. Peripheral neuropathy is most likely, but the slowing could be in the cauda equina. • Normal LP with prolonged LP–P37 interval: Abnormal conduction between the cauda equina and the brain. Median SEP is required to localize the abnormality to the spinal cord. Normal median SEP indicates a lesion below the mid-cervical cord. Prolonged median SEP indicates a lesion above the mid-cervical cord. A second lesion below the cervical cord cannot be ruled out, however, since the P37 latency is already prolonged by the higher lesion.
  • 27. • Prolonged LP and prolonged LP—P37 interval: This suggests two lesions affecting the peripheral nerve and central conduction. A single lesion of the cauda equina is possible.
  • 28. Clinical Correlations • Transverse Myelitis Transverse myelitis produces slowing of SEPs that depends on the site of the lesion. Lesion in the lower cervical or thoracic cord increases central conduction time without having an effect on brain conduction time. With recovery, the SEPs abnormalities are improved, but may not return to normal.
  • 29. • Multiple Sclerosis SEP is abnormal in most patients with MS, and can be supporting evidence for a silent lesion or confirmatory for a myelopathy. The most common finding in MS is an increase in CCT of the tibial SEP with normal peripheral conduction (LP). This is because the tibial SEP is assessing conduction along the longest myelinated nerve tract of any of the evoked potentials. BCT of median nerve SEP is less commonly increased than tibial nerve SEP CCT. A combined increase in BCT and CCT can be due to tandem lesions, but also can be due to a single lesion in the cervical cord.
  • 30. • Peripheral Neuropathy Peripheral neuropathy slows peripheral conduction (N9 and LP) with normal BCT and CCT. The N9–P14 interval may be prolonged with lesions affecting the proximal portions of the nerves, such as Guillain–Barré syndrome (GBS). GBS may also occasionally prolong CCT, presumably by affecting the afferent nerve roots of the cauda equina.
  • 31. • Vitamin B12 Deficiency Subacute combined degeneration from vitamin B12 deficiency delays or abolishes the cervical and scalp SEPs. With treatment, the abnormalities improve, although not completely to normal. This parallels the clinical course, where there is improvement but also some persistent deficit.
  • 32. • Spinal Cord Injury Cord transection abolishes potentials above the lesion, but most lesions are incomplete, so the defect in the SEP is variable. Lesions affecting position sense are most likely to alter the SEP. SEP is not perfectly sensitive so many patients may have undetectable scalp potentials despite preservation of some cord function
  • 33. • Brain Death Brain death is usually evaluated by EEG or blood flow studies, so the SEP is not typically used as a confirmatory test. In brain death, the scalp potentials are absent, usually with preservation of cervical potentials.
  • 34. • Stroke SEPs are not commonly used for evaluation of stroke, but if performed, will show attenuation, delay, and often absence of scalp potentials with stimulation of the limbs of the affected side. Lesions of the motor-sensory cortical regions are much more likely to produce abnormal SEPs than lesions elsewhere in the brain. In general, the severity of the stroke deficit correlates with the degree of abnormality of the SEP, but wide variation is common. SEP may be absent with subtle deficit and SEP may be preserved with major deficit.
  • 35. • Other uses • Monitoring during temporary clipping in aneurysm surgery has shown that a very prompt loss of cortical SSEP response (less than 1 minute after clipping) is associated with development of permanent neurologic deficit. • SSEP in spinal surgeries has become standard care of monitoring. • Monitoring during carotid endarterectomy. Intraoperative SSEP changes are used as an indication for shunt placement and to predict postoperative morbidity.