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 heart attack, severe asthma, smoke or carbon monoxide inhalation, high altitude exposure, strangulation, anaesthetic accidents, or poisoning.
In severe cases of anoxia and hypoxia, from any cause, the patient is often comatose (in a state of unconsciousness) for periods ranging from hours to days, weeks or months. Seizures, myoclonic jerks (muscle spasms or twitches), and defects of muscle strength and sensation may occur.
Depending on the severity of the injury, recovery may occur if the patient's respiratory and cardiovascular systems can be supported properly. As recovery proceeds, a variety of psychological and neurological abnormalities may appear, which may persists for a time and may improve. Mental confusion, personality regression, parietal lobe syndromes, amnesia, hallucinations, memory loss, and persistent myoclonus may also occur.
Treatment of anoxia and hypoxia consists of establishing an adequate airway as soon as possible, using enough oxygen to saturate the blood, supporting the cardiovascular system as needed, and preventing or treating pneumonia. Respiratory assistance may be necessary.
Reviewed by Dr Andrew Rose-Innes, Yale University School of Medicine, 2007