Seventeen years ago, on the first night that Dr. Gina Piazza was working at Lincoln Hospital in the Bronx, New York, she and other emergency room physicians had to treat victims of eight separate shootings arriving at around the same time.
"I think we saved everybody," Piazza said.
That incident was the largest group of shooting victim casualties Piazza has had to deal with at one time in her career.
On Monday morning, Piazza, now working in Augusta, Georgia, woke up to hear about a much larger incident.
Hospitals in Las Vegas were dealing with hundreds of shooting casualties, the victims of a gunman who opened fire on attendees of a country music festival from the 32nd floor of the Mandalay Bay Resort hotel.
"It's horrendous," said Piazza, co-chair of the High Threat Task Force at the American College of Emergency Physicians, who also helped respond to victims of the Sept. 11 terror attacks in New York City.
By midday Monday, officials said Las Vegas hospitals were treating a staggering 515 casualties, as the death toll grew to 58.
"As the numbers go by, the numbers continue to increase," said Clark County Sheriff Joseph Lombardo.
But Nevada Gov. Brian Sandoval said that medical workers "have told me they've saved lives" in the aftermath of the shooting.
Piazza said that since the 9/11 attacks, "hospital preparedness" for events involving mass casualties "has only been increasing."
She said that hospitals nationwide prepare for dealing with "any sort of mass casualty incident," which can include not only shootings, but also hurricanes, chemical spills and leaks, and other events.
"And because no one hospital can necessarily handle the extreme number of casualties as seen last night, we have to prepare as regions," Piazza said.
She said groups of hospitals in geographic areas often run drills to simulate mass casualties and the medical response to them.
In July, University Medical Center of Southern Nevada, the Las Vegas hospital that is the only Level-1 trauma center in the state, hosted a mass casualty training session that drew first responders from around the area. UMC is where many of the victims of Sunday's shooting were taken.
Dr. Gary Parrish, an Orlando, Florida-based physician who had dealt with victims of the Pulse nightclub massacre in 2016, spoke at the July event. Before Sunday night's shooting spree in Las Vegas, the attack at Pulse was the largest mass shooting in U.S. history.
"It's very important for facilities to practice," Parrish told Fox5 Las Vegas, for a story last summer on the event. "They have to practice, practice, practice."
Toni Mullan, a nurse at UMC, told Fox5, "It's not a matter of if, it's when."
Mullan noted that UMC and other Vegas hospitals had to deal with two mass casualty events in the past two years. One involved a crash of a school bus. The other involved a woman driving up on a sidewalk on the Las Vegas Strip, killing one person and injuring dozens more.
"I had the CEO [of the hospital] handing out blankets," Mullan said of the aftermath of the sidewalk crash.
"Our marketing people were handling crowd control."
On Sunday night, the sheer number of victims overwhelmed emergency medical workers and led civilians at the scene to take matters into their own hands in some cases.
One group of civilians tending to people suffering injuries at the scene reportedly asked a woman, Lindsey Padgett, to use her truck to take the victims to a hospital.
"We just need to get people over to the hospital," a man said to Padgett, video posted on Facebook shows.
"OK, put'em all in the back," Padgett responded.
The volunteers packed as "many people in their truck as they could," Padgett told Chicago TV program "WGN Morning News."
Piazza of the American College of Emergency Physicians said, "We all have our limits."
"There are just so many stretchers that a hospital has," she noted.
To prioritize patients, first responders and hospital staff use triage, evaluating who needs emergency treatment immediately, who can wait a bit longer, and who can wait beyond that.
Piazza said triage is done at the scene of a mass casualty, and then again when patients arrive at a hospital, and throughout the following hours.
"The most serious level of patient would need to be seen within minutes or an hour," she said.
Other patients, with non-life-threatening injuries, may need to wait six to eight hours.
"Our goal is to identify those who need immediate care, and treat them first," Piazza said.
While that is the goal, it sometimes is not achieved at the scene of a mass shooting.
An article in 2016 in the journal Critical Care reviewed studies of "re-hospital management of mass casualty civilian shootings."
The article noted that "triage at mass shooting incidents can be complicated by the ongoing threat and the mechanism of injury."
"Superficial wounds with minimal visible bleeding may be overlying extensive internal damage and internal haemorrhage and the same is true for reverse; severe surface injuries do not always indicate extensive damage of internal organs," the article said.
The article also noted that in the mass shooting at Virginia Tech in 2007, "the rate of over-triage was 69% measured as patients assigned priority 1 at triage who actually had an Injury Severity Score (ISS) of less than 15."
"High levels of over-triage may deprive severely ill patients of the resources needed to treat them," the authors wrote.
In Las Vegas, the casualty level is so high that officials have asked for people to donate blood for the victims being treated.
"We need blood," Sandoval said.
Officials asked that donations be made only at facilities operated by United Blood Services as well as at University Medical Center.
The Las Vegas Review-Journal reported that there was a six-hour-long line of people waiting to donate blood at United Blood Services, and that the center has signed up people to donate through next Monday.