What is the role of somatosensory evoked potentials (SEPs) in the evaluation of a comatose patient?

Updated: Aug 20, 2019
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Answer

SEPs are useful in the evaluation of a comatose patient, not only for diagnostic purposes but also for prognosis. In addition to EEG, other neuromonitoring tools, such as SEPs, have a complementary role, surveying the integrity of the neuroaxis as an indicator of prognosis or illness progression in both acute brain and spinal injuries. [8] Central conduction times are not affected significantly by level of consciousness, hypothermia, or sedative-hypnotic medications such as barbiturate anesthesia. Thus, SEPs are often useful in conditions in which clinical examination is of limited value. A favorable outcome is expected in about 53% of comatose patients with hypoxic-ischemic encephalopathy and in 49% of patients with traumatic brain injury coma who have preservation of bilateral cortical SEP responses.

Rothstein has shown that median SEPs supplement and enhance neurologic examination findings in anoxic-ischemic coma and are useful as an early guide in predicting outcome. Greater use of SSEP in anoxic-ischemic coma has been recommended to identify those patients unlikely to recover and can be cost effective. [9] A pilot study done by Bouwes et al has revealed that bilaterally absent cortical N20 responses of median nerve SEPs performed during mild hypothermia after resuscitation can predict a poor neurologic outcome. A larger multicenter prospective cohort study to confirm these results is in progress by the same authors. [10]

The absence of cortical responses bilaterally is associated with an unfavorable prognosis (ie, an outcome of persistent vegetative state in the vast majority of patients). Unilateral preservation of cortical SEP responses offers hope for a favorable outcome. Determination of presence or absence of the N70 in patients with postanoxic coma gives additional information about the likelihood of poor outcome, but it is not precise enough to base treatment decisions solely on its absence.

Combination of clinical examination, electroencephalography reactivity, and serum neuron-specific enolase offers the best outcome predictive performance for prognostication of early postanoxic coma; somatosensory-evoked potentials do not add any complementary information. Although prognostication of poor outcome seems excellent, future studies are needed to further improve prediction of good prognosis, which still remains inaccurate. [11]


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