SUNDAY, Jan. 23 (HealthDay News) -- The beginning of Rep. Gabrielle Giffords' intensive rehabilitation may be delayed until the end of this week because of fluid buildup in her brain, one of her doctors said Saturday.

Dr. John Holcomb, a trauma surgeon and retired Army colonel, told UPI that they will have to decide whether a catheter draining the fluid can be removed and Giffords can be transferred to the reknowned Institute of Rehabilitation and Research in Houston, or if a permanent shunt needs to be inserted. On Friday, Giffords was flown to Houston to begin her long road to recovery following a gunshot wound to her brain two weeks ago.

"No one expects her to go rapidly to TIRR," Holcomb, vice chair of surgery and chief of the acute-care surgery division at the University of Texas Medical School at Houston, told UPI. "We just have to wait and see if the fluid buildup issue resolves itself."

The fluid buildup had decreased some on Saturday and doesn't appear to be infected, he added.

Last week, staffers at University Medical Center in Tucson brought the 40-year-old Giffords to a deck at the hospital, where she breathed fresh air and felt the sun, trauma surgeon Dr. Peter Rhee said, the Associated Press reported.

"I saw the biggest smile she could gather," Rhee said. "We are very happy to have her enjoying the sunshine of Arizona."

Giffords has been making surprisingly strong progress since she was shot in the head Jan. 8. Her doctors in Tucson highlighted other signs of her continuing improvement -- she scrolled through an iPad, identified different colored objects and moved her lips. Still, they aren't sure if she is mouthing words, and they don't know how well she can see, the AP reported.

Her husband, astronaut Mark Kelly, believes she has tried to speak and can recognize those around her. "I can just look in her eyes and tell," Kelly said at a final briefing Thursday at the Tucson hospital. "She is very aware of the situation."

The encouraging medical updates out of Tucson indicate that Giffords has a high level of motor and emotional function, experts say.

"The fact that she is able to communicate, that she is able to stand and walk, the fact that she is moving both hands is a good thing," said Dr. Kester Nedd, an associate professor of neurology and director of neuro-rehabilitation at the University of Miami Miller School of Medicine.

"Motor function is a very strong predictor of outcome," he said. In addition, her ability to express emotion and interpret human interactions, which are some of the highest levels of cognitive function, means her chances of recovery are very good, Nedd added.

Giffords was one of 18 people shot by a gunman outside a Tucson supermarket. Six people died. On Wednesday, a federal grand injury indicted the suspect, Jared Loughner, 22, of Tucson, on charges of attempting to assassinate Giffords and trying to kill two of her aides.

Giffords' rehabilitation will take place at TIRR Memorial Hermann Hospital in Houston. This is one of the best rehabilitation centers in the country, said Dr. Steve Williams, chief and chairman of the department of rehabilitation medicine at Boston Medical Center and professor and chairman of rehabilitation medicine at Boston University School of Medicine.

"The key things with neurological injuries are when people begin to show signs of recovery very early," Williams said Thursday. "Very early in the ER she was able to squeeze the physician's hand and she has responded to simple commands, and yesterday she was standing."

"The issue is really going to be cognitive function, which is complex reasoning and abstract thinking," added Williams, who was not involved in her treatment but has studied the injury reports so far made public.

Physically, Giffords is making great progress, Williams said, but the full extent of her injuries is still unknown.

Nedd noted that Giffords is already starting at a very high level of functioning. "She was blessed," he said. "A lot of the force of the bullet that struck her was dissipated by the skull and the bullet exiting," he said. Also the injury was not to the deep brain, he added.

Once Giffords is settled in Houston -- where her astronaut husband lives -- the medical staff will evaluate Giffords' physical and mental abilities, Williams said.

One of the first steps in rehabilitation is to help patients regain the ability to take care of themselves. "This is called activities of daily living," Nedd said.

Giffords' rehabilitation will most likely center on her speaking ability and the processes of thinking, Williams said. She may be given medications, such as Ritalin, to stimulate the brain, he said.

One rehab goal is to retrain the brain to take over functions that may have been lost or damaged by trauma, experts said. This is done through repetition, Nedd said. "The brain has the ability to shift function from one part of the brain to another," he said.

Giffords will probably remain at TIRR Memorial Hermann for a month or two, then continue rehabilitation on an outpatient basis, perhaps for a year or more, Williams said.

Giffords, a Democrat, was elected to the House of Representatives in 2006.

Her survival has astounded experts, including Dr. David Langer, director of cerebrovascular research at the Cushing Neuroscience Institutes, part of North Shore/Long Island Jewish Medical Center in Great Neck, N.Y.

Ninety percent of people with gunshot wounds to the head die, said Langer.

More information

For more information on traumatic brain injury, visit the U.S. National Institutes of Health.