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Spinal Cord Monitoring
Dr. M. FennellyConsultant AnaesthetistThe Royal National Orthopaedic Hospital
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Why do I wantto know about
this?!!
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How?
Stagnara ‘Wake up test’Ankle clonus testNeurophysiological
-Evoked potentials
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Intra-operative physiological monitoring
Spinal cord (Scoliosis)Sciatic/ Femoral nerve (THR)Brachial plexusPedicle screwsVascular surgeryParotid surgery
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Concept of monitoring
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…….Indirect mechanical
Mechanisms of Injury ……
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L4L4
L5L5
Mechanisms of Injury ……
Direct mechanical
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aorta Segmental a.
Radicular a.Anteriorspinal a.
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Mechanisms of injury
Ischaemic cord injuryCompression
+Distraction
+Oedema
+Hypotension
=Reduced cord perfusion
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Epidural spinal somatosensory evoked potential Cortical somatosensory evoked potentialsC2 somatosensory potentials
( To posterior tibial nerve, peroneal nerve stimulation)
Somatosensory Evoked Potentials
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Preoperative electrode placement
Out of surgical fieldAnterior approach surgerySpinally injuredSpondylolisthesisBrachial plexus exploration
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Anaesthetic considerations for SSEP
Relatively forgivingRelaxation unimportant
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Effects of local anaesthetics and opiateson S.S.E.P.
Loughnan, Fennelly et al. Anaesthesia and analgesia 1995
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S.S.E.P. or M.E.P. ?
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Motorend-plate
M.E.P.
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WHY ?
Dissociation of SEP and MEPEarlier prediction of damageSpecific pathway monitoring
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M.E.P. Problems
•Anaesthetic•Stimulus patterns
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Anaesthesia
Nitrous oxideIsoflurane
Muscle relaxation
Propofol infusionFentanylAlfentanilRemifentanil
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Factors affecting E.P.s
HypoxiaHypotensionCarbon dioxideTemperatureNerve integrityAnaesthetic agentsSide
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Interpretation
What is a significant change?LatencyAmplitude 50%Other parameters
N.B. Must monitor minimum 20 minutes after final correction
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Action
Exclude technical failureExclude anaesthetic changeRelease correction / distraction(Decompress)
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How long have you got ?
Aortic cross clamp 30 minutes
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Why is the S.M.E.P. more sensitive toanaesthetic agents
Than the S.S.E.P. ?
Synapses in pathway
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History at RNOH...
Sensory nerve conduction in the human spinal cord: epidural recordings made during scoliosis surgery.Jones SJ. Edgar MA. Ransford AO.Journal of Neurology, Neurosurgery & Psychiatry. 45(5):446-51, 1982 May.
Spinal cord monitoring in scoliosis surgery. Experience with 1168 cases.Forbes HJ.Allen PW. Waller CS.Jones SJ.Edgar MA.Webb PJ.Ransford AO.Journal of Bone & Joint Surgery - British Volume. 73(3):487-91, 1991 May.
Temporal summation--the key to motor evoked potential spinal cord monitoring in humans.Taylor BA. Fennelly ME. Taylor A. Farrell J.Journal of Neurology, Neurosurgery & Psychiatry. 56(1):104-6, 1993
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