SUNDAY, Jan. 16 (HealthDay News) -- Arizona congresswoman Gabrielle Giffords underwent surgery Saturday to replace the breathing tube that had been in place since she was shot through the head a week ago in an attack in Tucson that killed six people.

Giffords had been breathing on her own, but the breathing tube had been left in place as a precaution. In its place, surgeons inserted a tracheotomy tube in her windpipe, protecting her airway and allowing her to be disconnected from the ventilator, according to officials at University Medical Center in Tucson, where Giffords is being treated.

Doctors also inserted a feeding tube. Both procedures, according to the hospital, are common in people hospitalized with brain injuries.

The hospital issued a statement saying that Giffords's "recovery continues as planned." She remains in critical condition.

Her doctors said earlier that, once the breathing tube was removed, they would be able to assess whether she could speak.

On Friday, doctors said Giffords was "continuing to make all the right moves in all the right directions" toward recovery. The Wall Street Journal reported that she has defied the odds and continued show improved function day by day.

"She is beginning to carry out more complex sequences [of movement] in response to our commands, and even spontaneously," said Dr. Michael Lemole Jr., neurosurgery chief at Tucson's University Medical Center. "We couldn't have hoped for any better improvement than we're seeing now."

Giffords' doctors say she has been opening her eyes more often since she first did so Wednesday. That was the day she also touched the wedding ring worn by her husband, astronaut Mark Kelly, after being asked by him to do so.

On Thursday morning, doctors said Giffords was able to keep her eyes open for up to 15 minutes at a time and could move her legs and one of her hands, the New York Times reported.

"She is doing some fairly specific things with her left hand," Dr. Peter Rhee, the hospital's chief of trauma, said at the time. "She is yawning. She is starting to rub her eyes."

Lemole also noted that Giffords could also "move both of her legs to command," the newspaper reported.

Doctors want to ensure that Giffords doesn't regress and are watching for pneumonia and blood clots, the Associated Press reported.

Experts also said that, despite her remarkable progress so far, Giffords may have suffered some permanent damage, but it's not yet clear how extensive that damage might be.

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., said: "She's probably going to survive in all likelihood, but months or even a year from now we may not know what her ultimate prognosis will be."

"She'll likely have a deficit in the near term, but we don't know if she'll end up in a wheelchair like James Brady [President Ronald Reagan's press secretary who was injured by a bullet during a 1981 assassination attempt on the president] or a functioning Congresswoman. We can't know," added Langer, who was not involved with Giffords' care.

Giffords was gravely injured, 13 others were wounded, and six people, including a 9-year-old girl, were killed in the shooting spree that took place in front of a Safeway supermarket in Tucson, where Giffords was meetings constituents. Jared Loughner, 22, faces multiple murder and attempted murder charges in the shootings. Giffords, a Democrat, was first elected to the House of Representatives in 2006.

The fact that Giffords is alive is a bit of a miracle.

According to Langer, 90 percent of people with gunshot wounds to the head die.

More information

The U.S. National Institutes of Health has more on traumatic brain injury.