Once oxygen is deprived, cells/tissue death starts to occur. The doctors were saying that after 45 minutes, enough brain tissue death would have occurred that your mother, while possibly able to be alive, would have no higher brain functions left. No one knows 100% for sure if there could ever be recovery.
http://www.city-data.com/forum/health-wellness/1505614-how-long-does-take-brain-die.html
Blood isn't what keeps the brain alive per se, but rather the dissolved oxygen in the blood. Typically, the human brain can go for about 3 to 5 minutes without oxygen before irreversible brain damage begins to occur, and 9 minutes is usually the point where brain death will occur and all electrical function stops. But in certain situations, the brain can go as long as an hour without oxygen.
http://www.answers.com/Q/How_long_does_it_take_the_brain_to_die_without_blood
The decrease of oxygen to at least one body part is known as hypoxia. The total lack of oxygen is known as anoxia. Brain cells are destroyed after 4 to 6 minutes without oxygen. When the flow of oxygen to the brain is completely cut off, a person will lose consciousness within 10 seconds. Extended hypoxia leads to brain damage and ultimately death.
http://www.ehow.com/about_5506985_long-can-brain-survive-oxygen.html
In the event that I or someone else were to die from something such as a heart-attack or stroke (Where you are dead and can't breathe). How long after a persons final breath would it be before brain cells start to die from a lack of oxygen? If the answer is that they start dying... show more To re-illiterate my question.
https://answers.yahoo.com/question/index?qid=20110819221555AAs3dgh
She suffered a massive stroke and was without oxygen to the left side of her brain for an undetermined amount of time. The neurologist explained that whether it was 20 minutes or 12 hours, the damage was done. The MRI films of her brain were devastating.
http://www.city-data.com/forum/health-wellness/1505614-how-long-does-take-brain-die.html
Breathing has always been synonymous with life. Our speech is permeated with idioms and phrases relying on the idea that taking a breath is the surest sign of vitality, and we constantly compare things we need to our body’s ultimate necessity: oxygen.
http://www.medicaldaily.com/breaking-point-how-long-can-someone-go-without-breathing-364450
> in the cell (and bloodstream) can be potentially fatal due to it's. > effects on pH (screws up enzymes and a whole slew of biochemical. > reactions) But when the brain is deprived of oxygen, metabolism shuts down.
https://www.quora.com/Why-do-neurons-die-so-quickly-when-deprived-of-oxygen
Quick Answer. According to TransWeb, people typically develop serious and possibly irreversible brain damage after 5 to 10 minutes of not breathing. Brain cells begin to die after 1 minute without oxygen. Serious brain damage is likely within 3 minutes without breathing.
https://www.reference.com/health/long-can-person-breathing-b64c2e2b8a4fb2be
Why do neurons die so quickly when deprived of oxygen? Brain damage sets in within 8 minutes of loss of oxygen. This is much faster than other cells of the body. For example with organ transplants, an organ can be removed, flown to another city, surgically implanted hours later, and survive.
https://www.quora.com/Why-do-neurons-die-so-quickly-when-deprived-of-oxygen
After five to ten minutes of not breathing, you are likely to develop serious and possibly irreversible brain damage. The one exception is when a younger person stops breathing and also becomes very cold at the same time. This can occur when a child is suddenly plunged into very cold water and drowns.
http://www.transweb.org/faq/q3.shtml
how long for brain cells to die without oxygen
The  brain cells to die 4 to 6 minutes  without oxygen. The brain cells to die in 4 to 6 minutes without oxygen.