Specifically, anoxia is a condition in which there is an absence of oxygen supply to an organ's tissues although there is adequate blood flow to the tissue. Hypoxia is a condition in which there is a decrease of oxygen to the tissue in spite of adequate blood flow to the tissue. Anoxia and hypoxia, however, are often used interchangeably -- without regard to their specific meanings -- to describe a condition that occurs in an organ when there is a diminished supply of oxygen to the organ's tissues.

Anoxia and hypoxia may be caused by a number of events, such as smoke or carbon monoxide inhalation, high altitude exposure, strangulation, anesthetic accidents, or poisoning. In severe cases of anoxia and hypoxia, from any cause, the patient is often stuperous or comatose (in a state of unconsciousness) for periods ranging from hours to days, weeks, or months. Seizures, myoclonic jerks (muscle spasms or twitches), and neck stiffness may occur.