Cerebral hypoxia occurs when the brain is deprived of oxygen for several minutes. Brain cells are extremely sensitive to oxygen deprivation. They can live about 4 minutes without oxygen, and after that, they begin to die. Hypoxia leads to widespread symptoms that can affect any area of the brain, but most often these symptoms affect the entire brain.
Level of Consciousness
Deprived of oxygen, people first become inattentive, then may lose consciousness. With prolonged hypoxia, coma and death may ensue. In coma, the patient is unconscious but some of his automatic brain functions are maintained. This state can last indefinitely and is then known as a persistent vegetative state. In brain death all brain functions have ceased except for cardiac function. Careful examination and re-examination of the patient is needed before establishing the diagnosis. Certain drugs, such as those used in anesthesia, can cause a state resembling brain death, but the patient will recover. When hypoxia doesn't cause unconsciousness, permanent brain damage rarely ensues.
Cognitive Deficits
If a person survives the episode of oxygen deprivation, he may have many deficits. Memory, attention and concentration are often impaired. Higher functions such as the capacity to think logically and to reason are damaged. Decision making is impaired. A previously normally functioning adult becomes more like a child. In Korsakoff's amnesia, which can occur when the temporal lobes are damaged, the patient can't retain new information. The doctor who visits him every day appears to him to be a new doctor who needs to be introduced every day all over again as though they'd never met before.
Motor Symptoms
Hypoxia can cause many types of motor difficulties, among them paralysis, weakness, unstable gait, stiffness and tremor. In unconscious patients, the pattern of paralysis can indicate to the physician the location and severity of the damage in the brain. As explained in "Harrison's Principles of Internal Medicine," lack of a motor response to pain in an unconscious patient on the third day after the injury indicates a very poor prognosis.
Other Symptoms
Seizures are common in persons who experience cerebral hypoxia. Blindness may occur as well. In some cases, the patient can see properly but can't recognize what he's seeing. A variety of psychiatric symptoms can appear, from irritability to agitation to depression. Personality can change beyond recognition.
References
- "Adams and Victor's Principles of Neurology"; Maurice Victor and Allan Ropper; 2001
- "Harrison's Principles of Internal Medicine"; Anthony Fauci et al.; 2008
