)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.
Antisialagogues are drugs or substances that decrease the flow rate of saliva and their effect is opposite to that of sialagogues. Their origin may be both natural and synthetic. Anticholinergics generally have antisialagogue effects, and most produce some level of sedation, both being advantageous in surgical procedures. Classic antisialagogues include:

atropine,
opium,
alkalies,
belladonna,
hyoscyamus,
stramonium,
tobacco in excess,
all nauseous or insipid substances. == References ==