One of the most difficult problems facing intensivists is understanding the natural history of comatose patients and their possibility of recovery. One must consider, among many factors, the patient's prior health, the acute illness, the patient's wishes, and the patient's prognosis. The patient's prognosis is the focus of this review. We posed the following question: What are the predictors of poor prognosis in comatose patients? In looking for indicators of a poor neurologic outcome, we ideally want a test with 100% specificity, but will accept lower sensitivity. That is to say, we would not want to predict a poor outcome and withdraw life support from a patient that might ultimately improve and survive to have a reasonable quality of life.

We systematically reviewed the literature with the intention of elucidating all clinical signs and all electrophysiological tests (e.g., electroencephalography [EEG] and evoked potentials, including brain stem auditory evoked potentials [BAEP] and somatosensory evoked potentials [SEP]) that correlate with a high chance of poor neurologic outcome in comatose patients. We divided the review into studies examining patients comatose as a result of hypoxic/anoxic injury, and those comatose as a result of traumatic head injury.