Predictive value of sensory and cognitive evoked potentials for awakening from coma.

Objectives: To determine the prognostic role of late auditory (N100) and cognitive evoked potentials (MMN) for awakening in a cohort of comatose patients categorized by etiology.

Methods: The authors prospectively studied a series of 346 comatose patients. Coma was caused by stroke (n = 125), trauma (n = 96), anoxia (n = 64), complications of neurosurgery (n = 54), and encephalitis (n = 7). Patients were followed for 12 months and classified as awake or unawake. Univariate and multivariate analyses were performed using regression logistic and Cox models.

Results: Pupillary light reflex, N100, middle-latency auditory evoked potentials, age, and etiology were the most discriminating factors for awakening. Statistical analysis showed that pupillary reflex was the strongest prognostic variable for awakening (estimated probability 79.7%). The estimated probability of awakening rose to 87% when N100 was present and to 89.9% when middle-latency evoked potentials (MLAEPs) were present. It was 13.7% when pupillary reflex was absent in anoxic patients. When MMN was present, 88.6% of patients awakened. No patient in whom MMN was present became permanently vegetative.

Conclusion: Pupillary reflex is the strongest prognostic variable, followed by N100 and MLAEPs allowing a reliable model for awakening. The presence of MMN is a predictor of awakening and precludes comatose patients from moving to a permanent vegetative state. Evaluation of primary sensory cortex and higher-order processes by middle-latency-, late, and cognitive evoked potentials should be performed in the prognosis for awakening in comatose patients.