Coma and brain death

Coma and impaired consciousness are common presentations in neurocritical care. This chapter reviews the definitions of different levels of awareness and discusses the diagnosis and management of comatose patients. DEFINITIONS • ▪ Coma is a state of unresponsiveness to external or internal stimuli in which a patient lies with eyes closed unaware of the environment. Although this definition seems quite straightforward, coma actually lies on a continuum of disorders of consciousness. • Consciousness, defined as a state of awareness of both the self and the environment, is composed of two key elements: arousal and content. ▸ Arousal is mediated by the ascending reticular activating system that localizes to the rostral pons, midbrain, thalamus, and hypothalamus, and is characterized by wakefulness or alertness. ▸ Content, on the other hand, requires the higher-level structures of the cerebral cortex and its connections to subcortical white matter, and is composed of affective and cognitive functions such as attention, memory, motivation, and executive function. • RATING IMPAIRED CONSCIOUSNESS • Disruptions to either the reticular activating system or bilateral cortices can therefore result in impaired consciousness, and the extent of the damage determines where on the spectrum of consciousness a patient may lie. Several scales have been created to rate the severity of impaired consciousness.