Altered mental status is due to neuronal dysfunction on a cellular level due primarily to inadequate oxygenation or glucose delivery to the cell. Abnormal vital signs are noted. Arrhythmias, especially atrial fibrillation and ventricular tachycardias, suggest an ischemic, toxic, or multifocal embolic etiology but also occur in dehydration or stress. Hypertension when extreme (diastolic greater than 120 mm Hg) can cause coma in hypertensive encephalopathy. A nonfocal neurological exam directs the work-up toward an etiology affecting the cortex diffusely, causing encephalopathy. Initial laboratory testing includes basic chemistries, glucose, creatinine, blood urea nitrogen, urinalysis and urine culture, and arterial blood gases. Administration of dextrose and thiamine is warranted in those patients in whom the etiology of the mental status change is unclear and the neurological examination is non-focal. The Glasgow Coma Scale has been shown to help prognosticate recovery in coma resulting both from trauma and out-of-hospital cardiac arrest.