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Transcranial Motor Evoked Potential Monitoring for Pediatric Spine Surgery

Introduction. There is a recognized risk of neurologic injury with spine surgery in childrenTrue incidence unknownRange 0.2-5%Gold standard to assess motor function has been, wake-up testDirect testing of motor functionSkilled team, cooperative patientSingle point in timeLate 1970's, early 19

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Transcranial Motor Evoked Potential Monitoring for Pediatric Spine Surgery

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    1. Transcranial Motor Evoked Potential Monitoring for Pediatric Spine Surgery Children Hospital and Regional Medical Center of Seattle K. Song, MD; D. Emerson, MD; M. Balvin, MS; N; J. Chen, MD; A. Bergeson, BA; N. Jiminez, MD; J. Slimp, MD

    2. Introduction There is a recognized risk of neurologic injury with spine surgery in children True incidence unknown Range 0.2-5% Gold standard to assess motor function has been, wake-up test Direct testing of motor function Skilled team, cooperative patient Single point in time Late 1970’s, early 1980’s, continuous monitoring of brain/spinal activity developed with the goal being to provide for early detection of neurologic change during surgical manipulation and to allow for countermeasures to change the outcome Various types of monitoring, SSEP, EMG, H-reflex

    3. Neural Monitoring Monitoring options have been SSEP - somatosensory evoked potentials False negative rate 0.13% False positive rate 1.5% Motor monitoring Late 1980’s NMEP - neurogenic motor evoked potentials Antidromic signal via sensory pathways False negative reports Transcranial Motor Evoked Potentials Developed in late 1980’s, early 1990’s. Initially intra-cranial procedures Allows true monitoring of cortico-spinal pathways Magnetic or electrical stimulation Upper extremities as controls All or none response Intersynaptic transmission means need to use total intravenous anesthesia (TIVA)

    4. Purpose Review early experience and learning curve using TcMEP Identify factors related to positive changes Identify reversal strategies for positive changes Determine sensitivity compared to SSEP if ture positive changes

    5. Methods 8/03 - 4/05 - 139 spinal deformity/tumor cases 84 attempted MEP/SSEP (78 spine deformity 6 tumor) Did not attempt to perform monitoring for: Known seizure disorder Nonamb., incontinent spastic quadriparesis Paraparetic myelodysplasia Spondylolisthesis/spondylolysis Idiopathic scoliosis 35 Congenital scolisis 4 Neuromuscular scoliosis 29 Acquired kyphosis 5 Congenital kyphosis 5 Intra canal tumor/syrinx 6 Technique CV2 stimulator (Caldwell laboratories) Separate consent - FDA approved 2/05 Stimulation sites; Left/Right cortex C3 and C4 sites Recording sites Thenar - wrist, Tibialis anterior - ankle, Toe flexors - heel

    6. Anesthesia This requires total intravenous anesthesia Propofol most commonly used Titratable Short acting Propofol infusion syndrome Opiates as adjunct Fentanyl/Remifentanyl Inhalational agents - interfere with monitoring. Need minimal dose and only at initation of case or will have problems Benzodiazepines Controlled hypotension more difficult Propofol Infusion Syndrome Is a fatal complication of high dose Propofol. Causes: Metabolic acidosis Lipemic serum (common) Irreversible bradycardia - asystole Associated with rate of infusion > 4.5 mg/kg/hr 200?g/kg/min - 50kg female = 24mg/kg/hr Associated with infusions > 24 hours Generally seen in ICU settings Case reports exist for short cases 3 hours

    7. Results Significant SSEP change definition 50% ? amplitude 10% ? latency Significant MEP change definition Complete loss, intact uppers Degradation > 75% with lack of response by voltage increase of 100 volts and adjustment of anesthesia Neuro Status 49 - Preop Normal ? Postop Normal 32 - Neuro abnormal preop ? No change postop 3 - Neurologically worse postop Intrapinal tumor, congenital kyphosis

    8. Results 17 pts. (20%) with variable/loss MEP - no deficit A/P fusion, Length of surg., MAP (p<0.08) 2/17 had abnormal SSEP Successful strategies to recover TcMEP Increase number of trains of stimulus Increase voltage of stimulus Raise MAP to > 50 Decrease Propofol infusion rate to < 200?g/kg/min. Release correction

    9. MEP Learning curve versus use of inhalational agents: As we used less inhalational agents, % positive MEP cases decreased relative to total number of cases.

    10. The impact of Inhalational Anesthetics

    11. Summary TcMEP is a useful, predictable, safe technique for motor monitoring There is a steep learning curve You need good anesthesia/monitoring with communication between them There can be a high rate of positives which may or may not be false, but are associated with: Low MAP High propofol flow Use of inhalational anesthesia Age of patient, younger > older for variability High sensitivity, ? High specificity Propofol infusion syndrome is a risk, but incidence is unknown. Alternative agents may include agents such as Etomidate?

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