The tragic near-drowning incident involving Whitney Houston and Bobby Brown’s daughter, Bobbi Kristina Brown, has sparked many questions pertaining to brain injuries. First let me express how deeply saddened I am by this unfortunate incident, and my heart and prayers go out to her family. I pray to God that this young woman, who has already endured so much tragedy in her short life, makes a full recovery from this horrific accident.

As details from what may have transpired on Saturday -- when 21-year-old Bobbi Kristina was found unresponsive, face down in a bathtub -- continue to emerge, many of you have written to me asking about brain injuries. While we don’t have the full details on exactly what happened to Bobbi Kristina, we do know CPR was administered and that she remains in a hospital “fighting for her life.” A source close to the situation told Fox411 that doctors have expressed that there is little they can do to help her. 

"It's now a matter of when the family wants to let go and accept that she's pretty much not going to make it," the source told Fox411. "They've left it up to the family as to how long they want to keep her alive." 

From a medical standpoint, there are some factors which must be considered in surmising what can occur in the brain during a near-drowning experience. First, we must consider how long the patient was without oxygen. Typically, if a patient has not received good oxygenation for greater than six minutes, the brain can suffer irreversible damage.

What I mean by irreversible damage is that brain function can either be completely or partially disabled. When the entire brain is completely disabled, we typically refer to that as brain death – which occurs when the upper brain areas and brain stem are no longer functioning. When the brain becomes partly disabled, the patient may have some structures of the brain working, like the brain stem, but not all. We typically refer to this state as a coma.

In order to differentiate between the two, physicians will conduct a full examination of the patient, which will includes checking vital signs, making note of underlying medical conditions, and considering how the brain failed to get enough oxygen, for instance was it due to a drowning, stroke, etc. The physician will then use several tests to determine the extent of brain function.

These tests typically include a full neurological examination, looking at the activity of the pupils, gag reflex, and possibly doing an apnea test – disconnecting the patient from the ventilator to see if the patient can spontaneously breathe on his or her own for several minutes. The physician will also do an electroencephalogram (EEG) test, to look for electrical activity in the brain, and conduct brain vascular imaging.

At the conclusion of the analysis, doctors will determine whether there has been partial or complete brain death. Many patients who have partial brain injury and are in a coma can theoretically progress to a more stable condition and partially recover. However, complete brain death tragically means death of the being.

Many people wonder why someone who has had a brain injury after they have been revived through CPR, can recover their heart function. While the heart can autonomically function as long as it is receiving oxygen, it is ultimately the brain which controls all. The brain dictates our breathing, neurological support and even our hormonal support, which ultimately regulates some of the major organs in our body including our kidneys. Without brain function, our bodies become quite vulnerable.

While we don’t have the details surrounding the medical condition of Bobbi Kristina, we do know how she was found, and the dangers of injuring the brain. We can only hope that she is able to make a full recovery after this tragedy. I wish her peace in her future, and continue to pray for her health.  

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.