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.