ERPs obtained with the auditory oddball paradigm in coma and altered states of consciousness: clinical relationships, prognostic value, and origin of components.

OBJECTIVE: To study the event related potentials (ERPs) in coma and altered states of consciousness, their relationship with the clinical status and coma outcome. METHODS: ERPs were recorded with a passive auditory oddball paradigm in 103 patients. Their probability of occurrence and the peak latencies and amplitudes were studied as a function of the Glasgow Coma Score (GCS). Their relationship with outcome was studied in a subset of 83 patients examined within the first 4 days, and expressed in terms of sensitivity, specificity, and negative or positive prognostic values. RESULTS: When present, the ERPs to rare stimuli consisted of a fronto-central negativity (N(endog), mean latency: 330 ms) and a fronto-central positivity (P(endog), mean latency: 431 ms) following the exogenous N100-P200 complex. Both their probability of occurrence and their latencies and amplitudes were related with the GCS in anoxic and traumatic comas. The N(endog) and P(endog) had high sensitivity with a negative predictive value of 70% and 100%, respectively, but a low specificity, with a positive predictive value of 44% and 41%, respectively. CONCLUSIONS: ERPs can be recorded in some comatose patients and are likely to reflect implicit orienting processes rather than preserved consciousness. Their presence implies a good prognosis but no conclusion can be drawn from their absence.