Electroencephalogram in the intensive care unit: a focused look at acute brain injury

The term spreading depolarization describes a wave in the gray matter of the central nervous system characterized by swelling of neurons, distortion of dendritic spines, a large change of the slow electrical potential and silencing of brain electrical activity (spreading depression). In the clinic, unequivocal electrophysiological evidence now exists that spreading depolarizations occur abundantly in individuals with aneurismal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage or traumatic brain injury. Spreading depolarization is induced experimentally by various noxious conditions including chemicals such as potassium, glutamate, inhibitors of the sodium pump, status epilepticus, hypoxia, hypoglycemia and ischemia, but it can can also invade healthy, naive tissue. Resistance vessels respond to it with tone alterations, causing either transient hyperperfusion (physiological hemodynamic response) in healthy tissue or severe hypoperfusion (inverse hemodynamic response, or spreading ischemia) in tissue at risk for progressive damage, which contributes to lesion progression. Therapies that target spreading depolarization or the inverse hemodynamic response may potentially treat these neurological conditions.

Background Previously published studies have reported that up to 43% of patients with disorders of consciousness are erroneously assigned a diagnosis of vegetative state (VS). However, no recent studies have investigated the accuracy of this grave clinical diagnosis. In this study, we compared consensus-based diagnoses of VS and MCS to those based on a well-established standardized neurobehavioral rating scale, the JFK Coma Recovery Scale-Revised (CRS-R). Methods We prospectively followed 103 patients (55 ± 19 years) with mixed etiologies and compared the clinical consensus diagnosis provided by the physician on the basis of the medical staff's daily observations to diagnoses derived from CRS-R assessments performed by research staff. All patients were assigned a diagnosis of 'VS', 'MCS' or 'uncertain diagnosis.' Results Of the 44 patients diagnosed with VS based on the clinical consensus of the medical team, 18 (41%) were found to be in MCS following standardized assessment with the CRS-R. In the 41 patients with a consensus diagnosis of MCS, 4 (10%) had emerged from MCS, according to the CRS-R. We also found that the majority of patients assigned an uncertain diagnosis by clinical consensus (89%) were in MCS based on CRS-R findings. Conclusion Despite the importance of diagnostic accuracy, the rate of misdiagnosis of VS has not substantially changed in the past 15 years. Standardized neurobehavioral assessment is a more sensitive means of establishing differential diagnosis in patients with disorders of consciousness when compared to diagnoses determined by clinical consensus.