• An 80% reduction in the ANAlitude of the dorsal column mediated incoming volley is required before the cortical SEP is reduced to <50% of baseline (“Cortical ANAlification”) (Eisen et al. 1982).
• For subcortical (cervical) waves, 60% reduction in ANAlitude carries up to a 10X risk of neurological complications.

Summary:

Upside of SSEP Monitoring:

• Well established criteria for reporting (gold standard).
• Well understood effects of anesthesia.
• Can be done with paralytics.
• High sensitivity (false negatives as low as 0.063%, Nuwer et al 1995).
• High negative predictive value (as high as 99.93 % Nuwer et al 1995).

Downside of SSEP Monitoring:

• Requires time consuming averaged signals (delayed results).
• Monitors only the dorsal columns / dorsal cord.
• Not recordable in presence of peripheral neuropathies.
• Very sensitive to electrical noise.

Last Word on SSEPs:

• SSEPs remain the ‘gold standard’ for spinal monitoring and are likely the most frequently used monitoring modality.

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