Lecture Notes: Integrating Neuroanatomy and Intraoperative Monitoring (IOM)

Semester Overview

• Semester Structure: Combining neuroanatomy and IOM with some separate lectures in anesthesia, IOM, and anatomy.
• Teaching Approach: Start with common modalities, application, and anatomical pathways.

Key Concepts for CNIM Exam Preparation

• Generator Sites: Understand which anatomical structure generates the waveform seen on the screen.
• Resolving Waveforms: Techniques to ensure responses from generator sites pass through operative areas correctly.
  • Identify iatrogenic events using waveform responses.

Somatosensory Evoked Potentials (SSEPs)

• Importance: Common tool used in surgeries to detect lesions or disruptions in function.
• Process: Stimulation at one point, recording responses at another.

Anatomy of SSEP Pathways

• Pathways: From wrist/feet up to cortex.
• Generator Sites: Understanding is essential for accurate monitoring.

Troubleshooting and Monitoring

• Subcortical vs. Cortical Responses: Subcortical less impacted by anesthesia than cortical.
• Anesthesia Impact: Bilateral changes usually indicate anesthesia effects, particularly on cortical SSEPs.
• Positioning Issues: Can cause changes in SSEPs, such as neuropraxia.

Troubleshooting and Technical Accuracy

• Avoid Assumptions: Always verify whether changes are due to anesthesia, technical issues, or surgical interference.
• Technical Checks: Ensure stimulator function by checking peripheral responses.

Monitoring and Clinical Responsibility

• Ethical Monitoring: Alerting the surgeon at the first sign of significant changes.
• Patient Safety: Avoid assumptions that lead to false negatives.

Evoked Potentials and Averaging

• Why Average?: To improve signal-to-noise ratio, ensuring clearer waveforms.
• Avoiding Artifacts: Use appropriate repetition rates to avoid interference with 60 Hz electrical noise.

Important Text: "Neurophysiologic Intraoperative Monitoring"

• Recommended Reading: Chapter 2 for correlating with lecture material.

SSEP Generator Sites - Upper Extremities

1. Peripheral Response: Brachial plexus/Erb’s point (N9)
2. Spinal Nerve Root (N11): Entry to spinal cord
3. Dorsal Horn and Column (N13): Spinal cord response
4. Medial Lemniscus (P14): Lower brainstem response
5. Brainstem to Thalamus (N18)
6. Cortical Response (N20/P23): Cortex response

Blood Supply and Responses

• Blood Supply: Middle cerebral artery for cortical responses.
• Importance of Understanding Anatomy: Crucial for interpreting changes and maintaining accurate monitoring.

Additional Tips and Future Sessions

• Hands-On Practice: In simulator sessions, observe effects of anesthesia and technical issues.
• Upcoming Lab: 3 PM session on troubleshooting and simulator practice.