Can median nerve Somatosensory Evoked Potentials (SSEPs) be used as the sole criterion for determining brain death?

Median Nerve SSEPs for Brain Death Determination

Median nerve somatosensory evoked potentials (SSEPs) should not be used as the sole criterion for determining brain death, as they provide valuable complementary information but cannot replace the clinical examination required by established brain death criteria. 1

Role of SSEPs in Brain Death Determination

• The American Academy of Neurology lists the absence of central nervous system-depressant drugs and neuromuscular blocking agents as a prerequisite for brain death determination, with the physical examination remaining the cornerstone of diagnosis 1
• Bilateral absence of the N20 SSEP wave has been extensively studied for prognostication after cardiac arrest, but not as a standalone criterion for brain death 1
• SSEP recordings are prone to electrical interference, with documented cases of false absent N20 responses due to excessive noise that could lead to erroneous conclusions 1

SSEP Findings in Brain Death

• In brain death, characteristic destruction of N20 and rostral P13-P14 generators occurs, with variable rostral-caudal loss of lower generators 2
• Studies show that P14 amplitude is invariably lower in brain death than in coma, with the Fz-Pgz derivation (recording the most rostral part of P14) being most reliable for distinguishing between coma and brain death 3
• Serial recordings demonstrate that subcortical SEPs deteriorate during the evolution toward brain death, with P14 amplitude decrease paralleling the clinical brain death syndrome 4

Limitations of SSEPs for Brain Death Determination

• SSEP findings must be interpreted with caution as they can be affected by:
  • Electrical interference that may lead to undeterminable recordings 1
  • Systemic effects like hypoxia or hypothermia that can alter SSEP components 4
  • Technical factors including electrode placement and reference selection 3

Current Recommendations for Brain Death Determination

• Brain death is legally defined as "irreversible cessation of all functions of the entire brain, including the brain stem" according to the Uniform Determination of Death Act 1
• The clinical examination remains the most important component in determining brain death, and must be performed with precision 1
• Confirmatory tests like SSEPs should supplement, not replace, the clinical examination when:
  • The clinical examination cannot be fully performed (e.g., facial trauma)
  • Confounding factors are present
  • Additional confirmation is desired 1, 5

Best Practice for Using SSEPs in Brain Death Evaluation

• SSEPs should be considered as one component of a multimodal approach to brain death confirmation 5
• When using SSEPs, bilateral absence of N20 responses with preserved peripheral potentials (N9) provides supporting evidence of brain death 2, 5
• The Fz-Pgz derivation has shown 100% reliability in distinguishing brain death from coma and may be recommended as a confirmatory test when other conditions affecting the lemniscal pathway are excluded 3
• SSEP interpretation should be performed by experienced neurophysiologists to avoid misinterpretation due to technical factors 1

Common Pitfalls to Avoid

• Relying solely on SSEPs for brain death determination without completing the clinical examination 1
• Performing SSEP testing while neuromuscular blocking agents are still active, which prevents proper clinical assessment 1
• Misinterpreting technically inadequate recordings with excessive noise as true absent responses 1
• Failing to consider conditions that may mimic brain death SSEP patterns, such as high cervical cord lesions or focal bilateral lemniscal lesions 3