What is Hypoxic-Anoxic Brain Injury?

Why is oxygen important to us? Our bodies require oxygen in order to metabolize glucose. This process provides energy for the cells. The brain consumes about a fifth of the body’s total oxygen supply, and needs energy to transmit electrochemical impulses between cells and to maintain the ability of neurons to receive and respond to these signals.

Cells of the brain will start to die within a few minutes if they are deprived of oxygen. The result is a cascade of problems. In particular, the disruption of the transmission of electrochemical impulses impacts the production and activity of important substances called neurotransmitters, which regulate many cognitive, physiological and emotional processes.

There are many neurotransmitters, and they perform a wide variety of important functions, although the specific ways neurotransmitters work is not fully understood. Some, such as serotonin, dopamine and norepinephrine, play an important role in regulating moods. Endorphins are critical for controlling pain and enhancing pleasure, while acetylcholine is important for memory functions.

A variety of disease processes and injuries can cause HAI. The most common is called hypoxicischemic injury, also known as HII or stagnant anoxia. This occurs when some internal event prevents enough oxygen-rich blood from reaching the brain. While strokes and cardiac arrhythmia can both result in HII, the most frequent cause is cardiac arrest.

Anesthesia accidents and cardiovascular disease each account for just under a third of cardiac arrests, according to a 1989 study. Other possible causes are asphyxia, generally caused by suicide attempts or near-drownings (16 percent), chest trauma (10 percent), electrocution (6.5 percent), severe bronchial asthma (3 percent) and barbiturate poisoning (3 percent).

Occasionally, HAI is caused by anoxic anoxia, which is when the air itself does not contain enough oxygen to be absorbed and used by the body. This can occur at high altitudes, where the air is thinner than at sea level, but is extremely unusual otherwise. Another syndrome, toxic anoxia, involves the presence in the body of toxins or other substances that may interfere with the way an individual processes oxygen.

Another occasional cause of HAI is anemic anoxia, which can occur when someone does not have enough blood or hemoglobin, a chemical in the red blood cells, which carry oxygen throughout the body. Acute hemorrhage, chronic anemia, and carbon monoxide poisoning are conditions that can result in anemic anoxia.

Acute hemorrhage is essentially massive bleeding, caused, for example, by a gunshot or other wound. Chronic anemia is an ailment in which a person suffers from persistently low levels of red blood cells or hemoglobin. Carbon monoxide poisoning, which appears to damage parts of the brain controlling movement, occurs in suicide attempts using automobile exhaust, but can also happen due to malfunctioning furnaces and other accidents involving machinery and industrial equipment.