Hypoxia occurs when the brain is deprived of oxygen. This can be the result of: *Carbon monoxide poisoning *Head trauma *Drowning *Strangling *Complications of general anesthesia *Choking *Suffocation *Cardiac arrest. Since brain cells require a regular source of oxygen, they can become irreversibly damaged within minutes. Hypoxia lasting longer than five minutes can often put a person in a coma, or even lead to brain death.