About 90 percent of this type of injury prove to be fatal, doctors said, but physicians treating Giffords have said that she has been responding to commands, non-verbally.
Calderone, who has more than 20 years of experience, said the fact that the bullet stayed on one side of the brain -- the left side -- helped Giffords survive.
"The trajectory of the bullet, the caliber of the bullet and weapon that fires it plays a great role in whether or not a patient survives," Calderone said.
The doctor said the left side of the brain controls the ability to speak and to understand speech, but the next 48 to 72 hours is critical.
"If they're able to keep the swelling under control, then she should stand a good chance of maintaining that ability to speak, follow commands and move extremities," Calderone said.
It's not necessarily technology that's helps people recover from these types of traumatic injuries, he said. Doctors have learned new skills from the military to help save lives.
"As a precaution, they removed the left side of her skull to allow more room in case swelling did occur and that's something that's been done with more frequency in the last decade or two," Calderone said.
Calderone, who has treated these types of injuries, said even if Giffords does come through, the rehab process could take months if not years.