Cerebral hypoxia refers to a lack of oxygen supply to the cerebral hemispheres (the outer portion of the brain), but it is more typically used to refer to a lack of oxygen supply to the entire brain.
There are numerous causes of cerebral hypoxia. These include drowning, asphyxiation caused by smoke inhalation, very low blood pressure, strangling, injuries during birth, cardiac arrest (when the heart stops pumping), carbon monoxide poisoning, high altitudes, choking, compression of the trachea, complications of general anasthesia, and diseases that paralyze the respiratory muscles.
Brain cells are extremely sensitive to oxygen deprivation. Some brain cells actually start dying just under five minutes after their oxygen supply is cut. As a result, brain hypoxia can kill or cause severe brain damage rapidly. This is an emergency condition and the sooner medical attention is given and the oxygen supply restored, the lower the chances of severe brain damage and death.
In mild cases, hypoxia causes only inattentiveness, poor judgment, and motor in-coordination. Severe cases result in a state of complete unawareness and unresponsiveness where brain stem reflexes, including pupillary response to light and breathing reflex, stop. Only blood pressure and cardiac function are maintained. If this persists, brain death is inevitable. If the lack of oxygen to the brain is limited to a very brief period of time, coma may be reversible with varying levels of return to function, depending on the extent of injury. Sometimes seizures may occur, which may be continuous (status epilepticus).
Cerebral hypoxia can usually be deduced from the clinical history and examination. Testing is targeted at determining the cause of the hypoxia. Treatment depends on the underlying cause. Most importantly, basic life-support has to be ensured. Mechanical ventilation must be used to secure the airway; blood pressure must be supported with fluids, blood products, or medications; the heart rate needs to be controlled; and seizures treated (if they occur). If seizures occur, some medications are used to suppress them with variable degree of success, including phenytoin, phenobarbital, valproic acid, and general anesthetics. Sometimes cooling with blankets (hypothermia) is used because much of the brain damage in hypoxia is caused by heat, and those who suffer the condition (if it is caused by drowning in cold water, for example ) in cold temperatures have survived longer than those who were affected in higher temperatures. However, the benefit of this treatment remains to be established. Experimental drugs called "neuroprotectants" have not shown a significant benefit so far.