Monitoring of motor evoked potentials in C spinal surgery

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					 Monitoring of motor evoked
potentials in C-spinal surgery

 Chart No: 4213769
 Brief history:
1. The 19 y/o man had suffered from TA in May,2002
 and multiple trauma, including right F-T-P EDH with
 depressed skull fracture, left F-T-P SDH and ICH, and
 type II odontoid fracture was noted.
2. Emergency craniotomy and hematoma evacuation
 were done at that time.
3. Cranioplasty in June,2002; odontoid screw fixation in
   July; screw removal due to mal-alignment of odontoid
   process on August 6th; posterior bone fusion and Halifax
   fixation of C1-2 on August 12th; and right Kocher VP
   shunt on August 23th,2002 at 光田 hospital
4. After operation, GCS:E4M6V2
5. He received cranioplasty with mini-plate fixation on
   November at NTUH
6. This time, he was admitted for removal of C1-2 Halifax,
   C1 laminectomy and lugue fixation C0-3 with bone
Spinal surgery
 Induction: Fentanyl 100ug, Pentothol 300mg,
 Atracurium 40mg
 Intubation: lightwand stylet
 Monitors: pulse oximetry, ECG, capnography, invasive
 blood pressure, CVP, MEP
 Position: prone positionendotracheal tube position
 and fixation, free of pressure
 Maintain: total intravenous anesthesiaPropofol,
 Ketamine+Rapifan, Esmeron
Intraoperative spinal cord and nerve
root monitoring
Somatodensory evoked potentials
 Standard test of spinal cord function during various
 surgical proceduresdorsal and lateral columns; good
 correlation between SSEP and motor function
 The upper extremity SSEP monitor the brachial plexus,
 essential during procedures of the cervical spine,
 indirectly monitor peripheral nerve function
 The lower extremity SSEP assess overall spinal cord
 Criteria for significant changes in waveform:10% latency
 increase, 50% decrease in signal amplitude, and/or
 complete loss of potential
Motor evoked potentials (1)
 Stimulation techniques: (1) transcranial magnetic or
 electrical stimulation of the cerebral cortex (2)
 direct(epidural) or indirect(percutaneous) stimulation of
 the spinal cord
 Recorded: (1) from spinal cord using epidural
 electrodes (2) from mixed peripheral nerves using
 surface or subdermal electrodes neurogenic action
 potentials (3) from muscle compound muscle action
Motor evoked potentials (2)
 Vascular injury to the anterior spinal cord can
 occur motor deficit without a change in the
 sensory potential
 Intramedullary spinal cord tumor resection,
 vascular abnormalities, and correction of spinal
 Absence of the MEPs remedy and if no
 recovery of EPs wake-up test
Drawbacks of transcranial MEP
 Technically more demanding than SSEP
 Transcranial stimulation remains a controversial
 Lack of significant criteria for warning except
 neurogenic action potentials
Confounding factors
 Anesthetics: volatile anesthetics reducing
 amplitude, prolonging latency of EPs
 Temperature: hypothermia
 Hypoxia         cerebral ischemia
 Preexisting neurologic lesions
Inhalation agents
 Greatest depressive effect on evoked potentials
 Dose-dependent prolong the latency and
 decrease the amplitude of EP
 N2O decrease the amplitude of EP but have
 minimal effect on the latency of EP
Intravenous anesthetics
 Less effects on evoked potentials
 Thiopental, opioid and propofol depress MEP
 to a greater extent than do etomidate or
 A 2-mg/kg dose of thiopental decreased the
 MEP amplitude 42.8 percent, and subsequent
 doses caused a further dose-dependent
  Ketamine does not follow the basic
 anesthesia-related EEG pattern, and was
 desirable for MEP monitoring
Our anesthetic formula for MEP
 Ketamine 200mg + Rapifen 2mg in 20ml N/S run
 10~12 ml/hr
 Propofol 70mg//hr
 Esmeron 6mg/hr
 Selection of adequate neuromonitoring during
 spinal surgery is important
 Totally intravenous anesthesia and short acting
 agents is better
 Maintain anesthesia depth: TOF for controlling
 muscle relaxant dosage; BIS or EEG for
 monitoring hypnosis
 Combined monitoring of motor and somatosensory evoked
 potentials in orthopaedic spinal surgery. [Clinical Trial. Journal
 Article] Clinical Neurophysiology. 2002 Jul.
 Transcranial electrical motor evoked potential monitoring for brain
 tumor resection. [Journal Article] Neurosurgery. 2001 May.
 Spinal cord and nerve root monitoring during surgical treatment of
 lumbar stenosis. [Review] Clinical Orthopaedics & Related
 Research. 2001 Mar.
 Total intravenous anesthesia for intraoperative monitoring of motor
 pathways : an integral view combining clinical and experimental
 data Journal of Neurosurgery 2002 Mar
 Effects of four intravenous anesthetic agents on motor evoked
 potentials elicited by magnetic transcranial stimulation.
 Neurosurgery 1993
Thank You !!

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