Full consciousness is a state of awareness of oneself and one’s environment and the ability to respond or interact with the environment. Coma is a state of total lack of awareness and wakefulness accompanied by the inability to respond to vigorous stimulation. Between these two extremes, there is a full spectrum of different levels of awareness and responsiveness. Unconsciousness itself is not a diagnosis or disease but is a manifestation of various pathological processes. There are many causes of unconsciousness, including structural and metabolic alterations or diseases.

The rigid cranial cavity holds brain tissue, blood, and cerebrospinal fluid (CSF). The volume of these three components and the intracranial pressure (ICP) they create are normally in equilibrium. Increased ICP is a life-threatening situation that results from an increase in any or all of these components. Increased ICP is a common factor in many pathological conditions affecting the brain due to masses, head injury, infection, vascular insults, toxic and metabolic conditions such as fluid and electrolyte imbalances, and hypoxia. Regardless of cause, increased ICP affects cerebral blood flow, produces compression and distortion of structures, and shifts content. If left untreated, increased ICP causes decompensation of neurological function, leading to death.