)The second most common cause of coma, which makes up about 25% of cases, is lack of oxygen, generally resulting from cardiac arrest. The Central Nervous System (CNS) requires a great deal of oxygen for its neurons. Oxygen deprivation in the brain, also known as hypoxia, causes sodium and calcium from outside of the neurons to decrease and intracellular calcium to increase, which harms neuron communication. Lack of oxygen in the brain also causes ATP exhaustion and cellular breakdown from cytoskeleton damage and nitric oxide production.Twenty percent of comatose states result from the side effects of a stroke. During a stroke, blood flow to part of the brain is restricted or blocked. An ischemic stroke, brain hemorrhage, or tumor may cause restriction of blood flow. Lack of blood to cells in the brain prevents oxygen from getting to the neurons, and consequently causes cells to become disrupted and die. As brain cells die, brain tissue continues to deteriorate, which may affect the functioning of the ARAS.The remaining 15% of comatose cases result from trauma, excessive blood loss, malnutrition, hypothermia, hyperthermia, hyperammonemia, abnormal glucose levels, and many other biological disorders. Furthermore, studies show that 1 out of 8 patients with traumatic brain injury experience a comatose state. Pathophysiology
Injury to either or both of the cerebral cortex or the reticular activating system (RAS) is sufficient to cause a person to enter coma.The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain.
Moreover, the unconscious brain is able to interact with its surroundings in a meaningful way and to produce meaningful information processing of stimuli coming from the external environment, including other people.According to Hawkins, "1. A life is good if the subject is able to value, or more basically if the subject is able to care. Importantly, Hawkins stresses that caring has no need for cognitive commitment, i.e. for high-level cognitive activities: it requires being able to distinguish something, track it for a while, recognize it over time, and have certain emotional dispositions vis-à-vis something. 2. A life is good if the subject has the capacity for relationship with others, i.e. for meaningfully interacting with other people." This suggests that unawareness may (at least partly) fulfill both conditions identified by Hawkins for life to be good for a subject, thus making the unconscious ethically relevant. See also
Brain death, lack of activity in both cortex, and lack of brainstem function
Coma scale, a system to assess the severity of coma
Locked-in syndrome, paralysis of most muscles, except ocular muscles of the eyes, while patient is conscious
Persistent vegetative state (vegetative coma), deep coma without detectable awareness. Damage to the cortex, with an intact brainstem. Process Oriented Coma Work, for an approach to working with residual consciousness in comatose patients. Suspended animation, the inducement of a temporary cessation or decay of main body functions. References


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