A doctor caring for an 8-year-old boy whose arm was reattached after it was bitten off by a shark says he is still at risk of dying from brain swelling.

But Dr. Rex Northup said he is encouraged that Jessie Arbogast's brain still is not swelling, even though he has reached the point where the condition is most likely to occur.

"The big, big issue that has us all kind of walking on eggshells right now is this issue of brain swelling and the potential of actual brain death," Northup said in a press conference Tuesday morning at Sacred Heart Children's Hospital in Pensacola, Fla.

Northup said the next few days are crucial because brain swelling can lead to death if the pressure in the skull exceeds blood pressure, which would stop blood flow to the brain and cause death.

Jessie, of Ocean Springs, Miss., was swimming at Gulf Islands National Seashore in the Florida Panhandle Friday evening when he was attacked by a 7-foot bull shark, which tore off his arm.

Doctors were able to reattach the arm, but Jessie went into kidney failure on Sunday and has been undergoing dialysis since. He remains unconscious and in critical but stable condition.

Northup, chief of pediatric care at Sacred Heart, said Jessie arrived Friday night with no blood pressure, no pulse and damage to "literally his entire body" because of severe blood loss.

"Because of the shark injuries and loss of blood associated with that, his brain did go through a period of time with a very low amount of blood flow," Northup said.

Doctors said the electroencephalograph readings show brain activity akin to deep sleep rather than brain damage, and that sedatives being used were probably contributing to his continued unconsciousness.

"It has the appearance at this point in time of perhaps someone who is in a deep sleep, that there plainly is still electrical activity," Northup said. "He does seem to respond to things that are painful or bothersome to him."

"He has done a little bit of a spontaneous eye opening and blinking of his eyes," Northup said.

Although Jessie was still fighting for his life, his chances were much improved over the day he arrived at Baptist Hospital after the attack.

"Friday night I had a dead child," said Dr. Jack Tyson, one of the surgeons who reattached the arm at Baptist Hospital. "Now I have a child with a viable extremity that's warm, that's got a pulse."

Jessie's uncle, Vance Flosensier, of Mobile, Ala., wrestled the shark to shore after the Friday attack.

"He's a big guy. He got hold of it and tossed it ashore," District Ranger Supervisor John Bandurski said.

Ranger Jared Klein then shot the shark four times with a 9 mm pistol, and pried its jaw open with a police baton. Volunteer firefighter Tony Thomas used a clamp to pull the boy's severed arm out of the shark's gullet.

"Hero is what I can say about the aunt and uncle," Tyson said. "They took beach towels and tied off the arm and leg to try to control that bleeding, which is exactly the thing to do."

According to the International Shark Attack File in Gainesville, 34 of the nation's 51 reported shark attacks last year were in Florida. One of the attacks was fatal: A 69-year-old man was killed by a bull shark near his St. Petersburg home last August.

There were 79 shark attacks worldwide last year, including 10 that were fatal. File officials said it is the highest number since the organization began keeping records in 1958.

The Associated Press contributed to this report.