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Transcranial Motor Evoked Potential Monitoring for Pediatric Spine

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Transcranial Motor Evoked Potential Monitoring for Pediatric Spine Powered By Docstoc
					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
   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
                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)
                  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
                                    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
                                     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
                                     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

            Absent at     Variable     Stable     Lost           Lost no
            start of case Baseline     No ∆       Recovery       Recovery
    SSEP      7(8.%)*          5          68            3              1

    MEP       3(4%)^          10          61            7              3

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


           LIGATION                 MAP 51             LOSS AFTER
          SEGMENTAL                 MAP 60            LAMINECTOMY
       ARTERY With release     Propofol 200150
MEP Learning curve versus use of inhalational agents:
As we used less inhalational agents, % positive MEP
 cases decreased relative to total number of cases.
                              MEP Positive - No Deficit

         40
         35
         30
         25
                                                                         Series2
                                                                                    Pos MEP
         20
                                                                         Series1
         15
         10
          5                                                                          # cases
          0
              8/03 - 12/03   1/04 - 5/04   6/04 - 10/04   11/04 - 3/05




              100%

              90%

              80%
                                                                                   Inhalational
              70%

              60%

              50%

              40%

              30%                                                                   TIVA
              20%

              10%

               0%
                M 08




                Ju 8
                N 07

                D 07




                N 08

                D 08
                Ap 8
                Se 07

                O 7




                M 08




                Se 08

                O 8
                Ja 7




                        8
                 Ju 8
                Au 08
                Fe 8




                     -0
                     -0
                       0




                       0
                     -0




                       0




                     -0
                      0
                   b-
                     -

                     -




                     -

                     -
                   p-




                   p-
                   g-




                   g-
                   n-
                   r-




                    l-
                   n-




                 ay
                  ct
                 ov




                  ct
                 ov
                  ar
                  ec




                  ec
               Au
                            The impact of Inhalational Anesthetics
                        MEP STIMULATION: TIVA AGES 2-21                                                                ISO/SEVO-N2O,PROPOFOL: ALL AGES

         10                                                                                       10
         8                                                                                        8




                                                                                          TRAIN
TRAIN




         6                                                                                        6
         4                                                                                        4
         2                                                                                        2
         0                                                                                        0
              0   100     200      300          400       500     600         700                      0   100         200    300    400          500   600   700         800   900
                                      VOLTAGE                                                                                          VOLTAGE

                                         Series 1                                                                                          Series 1




 Voltage required to generate MEP greater with higher number of trains
 If inhalational agents used.
                            MEP STIMULATION: TIVA: AGES 9-21                                                             MEP STIMULATION: TIVA AGES 2-7

         10                                                                                       10
          8                                                                                       8




                                                                                          TRAIN
 TRAIN




          6                                                                                       6
          4                                                                                       4
          2                                                                                       2
          0                                                                                       0
              0   100      200       300            400     500         600         700                0         100          200           300         400         500         600

                                         VOLTAGE                                                                                       VOLTAGE

                                                                                                                                           Series 1
                                           Series 1




                   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
                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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