(CNN) -- Hospitals near Aurora, Colorado, were flooded with victims after a movie theater shooting Friday morning.
An Aurora Fire Department call log reveals the urgency of the situation.
"If they're dead just leave them," a voice tells a fire department responder who reported that police said there may be a number of people dead inside the theater. "We're in a mass casualty situation at this time. Please make sure that you guys set up some kind of transport officer over there that can contact the hospitals so we don't overload one."
The emergency department at Denver Health Hospital was chaotic as staff prepared for the arrival of patients from the shooting, said Dr. Christopher Colwell, director of emergency medical services there. The hospital received seven victims, but called in extra personnel and was ready to take in more patients.
"You're not sure how they're going to arrive to you, so you prepare for the worst," he said.
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Gunshot wound patients are fairly regular at Denver Health, although not on this scale, he said. In a mass shooting situation, staff assess the severity of the wounds and what steps must be taken -- some need to go straight to the operating room, others can wait, still others may not require surgery.
Colwell was a physician who treated victims at the scene of the Columbine High School shootings in 1999. Five patients were transferred to Denver Health; all survived.
"We have obviously done a lot of training exercises since then to try to prepare for an event like that," Colwell said.
Dr. Frank Lansville, medical director of emergency services at Aurora South Hospital, told CNN his hospital had seen 18 patients so far, 12 of whom suffered from gunshot wounds. There were several tear gas victims who were stable, he said. They had been seen, decontaminated and discharged. "The others had horrific gunshot wounds to various parts of their body," he said.
At Aurora Medical Center, the first victim of the movie theater shooting came in before the staff had even heard about the attack, said Tracy Lauzon, director of EMS and trauma services at the hospital.
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Soon after, the trauma surgeon learned more victims were headed their way. Four other trauma surgeons, two orthopedic surgeons and various other physicians came to help. Six patients have gone through surgery.
Aurora Medical Center has taken in 15 patients from the shooting, she said. Eight have been treated and discharged from the emergency room; the other seven were admitted.
"We do drills twice a year anticipating this kind of thing, so people are very well prepared and the hospitals are very well prepared," Lauzon said.
Most of the hospitals in the Denver area follow established federal guidelines for emergency response, said Nicole Williams, spokeswoman for Swedish Medical Center, which treated four victims from the shooting at the movie theater. "We were extremely prepared coming into this," she said because the hospital has already completed a couple of disaster drills this year.
During such a drill, a mass page goes out to the hospital administration alerting officials that EMS has multiple patients who could be transported to area hospitals, and the staff is told be on standby. Emergency workers call the hospitals to see how many beds are available and how many critical patients they can take.
Then, the hospital brings in essential staff, in addition to extra trauma surgeons or other specialists as needed.
"It's a very controlled atmosphere," Williams said. "We all try to stay very calm and just serve the community to the best of our abilities."
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Staff at Swedish Medical Center's command center fielded hundreds of phone calls "from very panicked people looking for their husbands, their wives, their children," Williams said.
Swedish Medical Center was still treating three patients for gunshot wounds: an 18-year-old male in fair condition, a 20-year-old male in critical condition and a 29-year-old female in critical condition. A fourth patient, a 19-year-old female, came in a few hours after the shootings with minor injuries, possibly caused by shrapnel. She was treated and released.
The family members of the victims at the hospital have been notified, Williams said. "All of the victims have loved ones -- family or friends -- by their side, while they're here," she said.
Kari Goerke, Swedish Medical Center's chief nursing officer, worked in the operating room in the aftermath of the Columbine shootings of 1999. Swedish Medical Center treated four Columbine victims, all of whom survived.
"We had them all in the operating room within an hour of the event," Goerke said. "That gives them much better chances."
The staff responded with expertise and compassion both in 1999 and on Friday morning, she said.
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"Afterwards you kind of think about what's happened and the shock and awe of the whole situation and how horrific it is," she said. Her voice cracked as she discussed the emotional aftermath. "Taking care of kids is always hard. I'm a mom, I can relate. That makes it difficult."
But, she added, "it's what we're trained to do."