Study Notes on Spontaneous and Triggered Electromyography with Train of Four

SPONTANEOUS AND TRIGGERED ELECTROMYOGRAPHY WITH TRAIN OF FOUR

Introduction

  • Confidentiality Notice: The information contained in this document is proprietary and confidential, intended for use in medical and research contexts.

Overview of Electromyography (EMG)

  • Electromyography (EMG): A technique used to study electrical impulses in muscles, which is used to assess motor nerve root integrity during spinal procedures.

  • Types of EMG Monitoring:

    • Spontaneous Electromyography (sEMG): Continuous signal recording from muscles using electrodes.

    • Triggered Electromyography (tEMG): Signal recording that is time-locked to specific intensity stimulation, yielding compound muscle action potentials (CMAP).

Anatomy Review

  • Spinal Nerve Roots:

    • Importance of muscle innervation from spinal nerve roots for understanding EMG in spinal procedures.

    • Cervical Nerve Roots: C1-C8, exit at levels above vertebra.

    • Thoracic Nerve Roots: T1-T12, exit at levels below vertebra.

    • Lumbar Nerve Roots: L1-L5, exit at levels below vertebra.

    • Sacral Nerve Roots: S1-S5, exit at levels below vertebra.

Cervical Spine Nerve and Muscle Summary

  • Level and Corresponding Muscles/Innervation:

    • C2: Sternocleidomastoid, Trapezius (Upper, Middle, Lower) – Spinal Accessory Nerve

    • C3: Trapezius (U/M/L) – Spinal Accessory Nerve

    • C4: Trapezius (U/M/L) – Spinal Accessory Nerve

    • C5: Deltoid – Auxiliary Nerve

    • C6: Biceps – Musculocutaneous Nerve

    • C7: Triceps, Extensor Carpi Radialis – Radial Nerve

    • C8: Abductor Pollicis Brevis, Abductor Digiti Minimi – Median and Ulnar Nerves

Thoracic Spine Nerve and Muscle Summary

  • Level and Corresponding Muscles/Innervation:

    • T1-T4: Intercostals – Intercostal Nerves

    • T5-T12: Upper and Middle Rectus Abdominus, Lower Rectus Abdominus, Obliques – Thoracic Nerves

Lumbosacral Spine Nerve & Muscle Summary

  • Level and Corresponding Muscles/Innervation:

    • L1 (L1-L3): Iliopsoas – Lumbar Plexus

    • L2-L4: Vastus Medialis, Vastus Lateralis, Rectus Femoris – Femoral Nerve

    • L5: Tibialis Anterior, Peroneus Longus – Deep Peroneal and Superficial Peroneal Nerves

    • S1: Gastrocnemius, Biceps Femoris, Abductor Hallucis, Abductor Digiti Minimi – Tibial, Sciatic, Medial Plantar, Lateral Plantar Nerves

    • S2-S4: External Anal Sphincter – Pudendal Nerve

Electrode Placements in EMG

  • Types of Electrodes Used: Twisted pair subdermal needle electrodes.

  • Montages:

    • Bipolar Montage: Both needles in the same muscle for specific measurements.

    • Referential Montage: Needles in different muscles for wider nerve root coverage.

    • Compound Montage: A combination of bipolar and referential for broader muscle coverage.

EMG Techniques and Settings

Spontaneous Electromyography (sEMG)

  • sEMG Monitoring: Recording continuous signals from muscles corresponding to nerve roots at risk during surgery.

  • Normal sEMG Response: Absence of activity, considered "quiet" EMG.

Triggered Electromyography (tEMG)

  • tEMG Mechanism: Uses the same channels as sEMG but expects a CMAP in response to stimulation (constant current).

  • Pedicle Screw and Direct Nerve Stimulation: Tests the integrity of nerve responses related to surgical procedures.

Train of Four (TOF) Stimulation

  • Define TOF: A method to assess levels of muscle paralysis using compound muscle action potentials recorded after a series of stimulations at a 2 Hz repetition rate.

  • Parameters:

    • Gain settings can be set at 3500 uV/Div; Sweep at 2 ms/Div.

  • Fade Measurement: Ratio of T4/T1 amplitudes to indicate paralytic levels.

    • Example assessment: 1.0/1.0 = 1.0 (No Fade), 0.5/1.0 = 0.5 (50% Fade).

EMG Anesthetic Requests

  • Neuromuscular Blocking Agents (NMBA): Requests for no NMBAs during critical surgical times.

  • Types of NMBAs: Short-acting for intubation preferred; longer agents may include Rocuronium or Vecuronium.

  • Documentation: Document instances of unreliable EMG.

TOF Protocols

  • MPOWERHealth Basic Protocols:

    • Reliability thresholds for tEMG, sEMG, and MEP.

  • Stimulation Setup: Approximately 2-3 cm electrodes placed at target nerve sites.

Troubleshooting Procedures

  • Common Issues:

    • Verify electrode placement accuracy and stimulation intensity.

    • Adjust settings based on the response obtained.

    • Ensure appropriate muscle targeting and avoidance of artifacts.

Spontaneous EMG Data Interpretation

  • Data Analysis Method (S.P.A.A.M):

    • S: Confirm surgical stage.

    • P: Recognize pathologies affecting signal responses.

    • A: Use audio feedback for nerve activity.

    • A: Confirm TOF anesthesia impacts.

    • M: Assess morphology of signals.

sEMG Activity Types

  • Types of Activity Noted:

    • Spikes elicited by external nerve contact or spontaneously.

    • Bursts indicating underlying issues.

    • Training activity linked with nerve irritation.

Conclusion

  • Understanding of EMG is critical for recognizing the integrity of nerve roots during spinal procedures. Regular monitoring and compliance to protocols improves both patient safety and surgical outcomes.