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Predicting the outcome of a comatose or poorly responsive patient is a major issue for intensive care unit teams, in order to give the most accurate information to the family and to choose the best therapeutic option. However, determining the level of cortical activity in patients with disorders of consciousness is a real challenge. Reliable criteria are required to help clinicians in the decision-making process, especially in the acute phase of coma. In this paper, we propose recommendations for recording and interpreting electroencephalography and evoked potentials in comatose patients based on the literature and the clinical experience of a group of neurophysiologists trained in the management of comatose patients. We propose methodological guidelines and discuss prognostic value of each test as well as the limitations concerning recording and interpretation. Recommendations for the strategy and timing of neurophysiological assessments are also proposed according to various clinical situations., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Three-modality evoked potentials (EPs) have been used for several years in association with the electroencephalogram (EEG) as a diagnostic and prognostic tool in acute traumatic or nontraumatic coma. In 1993 we proposed to combine these in two indices: the index of global cortical function (IGCF) and the index of brain-stem conduction (IBSC). Four EP patterns based on both indices emerge at the acute stage of severe head trauma. These are easily explainable by pathophysiology. Pattern 1 corresponds to alterations in the index of global cortical function without changes in the index of brain-stem conduction. Its prognosis is good (80 to 90% of these patients recover). Pattern 2 is characterized by alterations of somatosensory EPs that are suggestive of midbrain dysfunction. The prognosis depends both on the reversibility of the midbrain dysfunction and on the extent of associated diffuse axonal lesions, whose evaluation requires MRI. Patients who recovered from Pattern 2 sometimes did so after a long interval during which they remained vegetative. Pattern 3 is characterized by alterations of brain-stem auditory EPs that are suggestive of pontine involvement. It usually follows uncontrolled intracranial hypertension and corresponds to evolving transtentorial herniation. All patients with that transient pattern eventually died. Pattern 4 is categorized by the disappearance of all activities of intracranial origin, contrasting with the preservation of all activities of retinal, spinal-cord, and peripheral-nerve origin. This pattern corresponds to brain death. In our experience, three-modality EPs are currently the best bedside brain-death confirmatory tool.

CO2 laser stimulation of tiny skin surface areas on the hand dorsum generate ultralate laser evoked potentials (LEPs) with a major positivity maximal at the vertex at a latency of about 1 s. These potentials follow selective and direct activation of C-fibres in the superficial layers of the skin. To identify the endogenous P3 component in ultralate LEPs, we used a 2-stimulus oddball paradigm (20% probability of targets). Ultralate LEPs were recorded in eight healthy subjects with 19 channels EEG and EOG. Laser stimuli (n = 200/subject, < 0.5 mm diameter, 5 ms duration, 9.4 mJ/mm2 energy density) were applied in a pseudo-random order to the proximal phalanx of either middle finger (target) or index (non-target) of the left hand. Vigilance was maintained during recording sessions. Subject’s task was to press a button to any kind of sensation perceived at the target zone. We observed a negative-positive (N965-P1139) complex maximal at Cz for all stimulus conditions. This complex was of significantly larger amplitude for rare events. For the target responses, a second distinct positive peak was observed with a mean latency of 1343 ± 103.5 ms with maximum amplitude at Pz. This latest peak may represent an endogenous P3-like component as it is linked to the subject’s detection of the target stimulus (rare events). [Copyright &y& Elsevier]