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Transcranial Motor Evoked Potential Monitoring for Pediatric Spine Surgery

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. Introduction.

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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 • MEP loss 100% predictive deficit • ^1 MEP absent stable SSEP • *5 SSEP absent stable MEPs; 2 SSEP absent, MEP absent-both with neuro deficit

  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 Loss No Recovery Loss Recovery LIGATION SEGMENTAL ARTERY With release MAP 51 MAP 60 Propofol 200150 LOSS AFTER LAMINECTOMY

  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. Pos MEP # cases Inhalational TIVA

  10. The impact of Inhalational Anesthetics Voltage required to generate MEP greater with higher number of trains If inhalational agents used. For a given age with stable BP and uncomplicated case Younger children require higher number of trains and more variable voltage to generate MEP stimulation

  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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