The need to get the injured and the dying from the shooting site beside the Mandalay Bay Hotel and Resort to UMC and other hospitals was so great that civilians stepped in. The first patients who arrived, as Nevada trauma surgeon Jeremy Stahl writes for Slate, were "the people that were scooped up by the citizens here in Las Vegas in their vans and their pickup trucks. They drove them up here to the hospital very quickly... Then the ambulances started coming in. They had three or four people in each of the ambulances that they were dropping off."

Many stories are emerging of audience members, civilians and medical staff who put shooting victims in their own vehicles to get to hospitals quickly. A woman named Lindsey Padgett used her truck to ferry numerous victims to hospital, telling Chicago's WGN Morning News that they packed "as many people in their truck as they could." Paramedic Amber Ratto and her colleague loaded a husband and wife into the back of their private ambulance after getting news of the shooting from the Las Vegas Strip on Sunday night. "I taped [his wound] really, really hard and started multiple IVs to try to keep him alive," she told The Guardian. "His wife was was calling their daughter saying they had been shot but that it would be OK. In my head I was thinking, I sure hope so, because I don’t know. His body was completely pale and he was going into shock.”

One of the most distressing things about the medical reaction to the mass shooting in Las Vegas is that it had not only been anticipated, it had been trained for. UMC staff had hosted a mass session training in July, run by one of the doctors who'd been in trauma surgery after the Orlando Pulse nightclub shooting, giving them specific instructions on how to cope with a mass shooting event. "Because no one hospital can necessarily handle the extreme number of casualties as seen last night," Dr. Gina Piazza, co-chair of the High Threat Task Force at the American College of Emergency Physicians, told CNBC, "we have to prepare as regions." First responders from all over Nevada attended, and were instructed, among other things, to roll gurneys and wheelchairs out of the way because of the influx of patients. And after the Boston Bombing in 2013, first responders across the country were given training on how tourniquets can be life-saving in emergency mass casualty situations.

Hospitals also had "tagging" systems in place in triage to identify which patients needed critical life-saving help and which ones were severe but could afford to wait (many in UMC would end up waiting six to eight hours, some sitting on the floor because beds were full). Depending on the hospital, less serious cases are green or yellow, but patients in imminent danger of dying are always given the same color: red.

In situations where it's not clear if a shooter has been subdued, medical staff have to make choices about protecting their own safety. Emergency workers, the New York Times reports, went to the site of the shooting to help triage patients and get them to hospital while wearing ballistic helmets and protective clothing to avoid being shot themselves. Paramedics are also trained to avoid attracting attention; Amber Ratto told The Guardian that she and her colleagues turned off their vehicle lights and worked in darkness so as not to attract attention and risk further injury for their patients, or death themselves.

Despite training and highly prepared trauma units, the Sunday massacre stretched thin the resources and personnel limits of Nevada hospitals across the region. Toni Mullan, a clinical supervisor at the trauma resuscitation unit at UMC, had just come off a 12-hour shift, but told the New York Times that she drove back to UMC at 110 miles an hour and left her car smoking in the parking lot outside the hospital to assist. Entire staff were summoned back to hospitals, including huge quantities of cleaners to wash away the biological matter left behind by dozens of patients at once.

Medical staff went beyond their limits. The Chicago Tribune reports that pediatric surgeons operated on adults and obstetricians diagnosed trauma patients, while some surgeons were performing five operations simultaneously. One surgeon, Jay Coates, told the Associated Press, “I have no idea who I operated on. They were coming in so fast, we were taking care of bodies. We were just trying to keep people from dying. Every bed was full. We had people in the hallways, people outside and more people coming in.” Many patients came in unidentified, so names were assigned at random. Staff worked shifts back-to-back, and volunteers showed up to provide them with water and food.

Supplies were under constant pressure. UMC didn't have enough X-ray machines; at one point, the supply of chest tubes ran critically low and a nearby hospital ran them over on the back of a pickup truck, according to the Tribune. The New York Times reported that they also faced critical shortages of IV tubing, fluids, blood pressure cuffs and blankets. And medical staff were also operating under extreme psychological pressure. Stahl wrote that "probably the hardest thing I saw" was the police officer who died at his hospital:

"The police department was in there with him — they didn’t leave him. We had a morgue set up by the operating room. They had one officer in full uniform holding the American flag folded up, and he stood with that downed officer the entire time he was with us."

To civilians, hospitals in the wake of mass shootings with high casualty levels are as close as they might come to a theater of war. Paramedic Amber Ratto described the Sunrise Hospital & Medical Center as seriously distressing: “Blood just soaking the hallways, everywhere." Toni Mullan described it as "a disaster zone, a chaotic scene, very chaotic" to the New York Times, adding, “If a nonmedical person were to be sitting there watching this, they would think nothing was being accomplished.”

Accounts from doctors are consistent in one thing: how grisly the scene was. Cardiovascular technician Robert Smith recalls “blood on the ground in the car park — trails of blood about 20 feet from the entrance [of UMC]. That’s where they were dropping off the people.” UMC's director of emergency medicine Scott Scherr says he remembers blood pouring off gurneys, while trauma nurse Renae Huenig says "the air smells like iron... you're standing in a pool of blood trying to care for your patient, slipping and sliding. Soon you're covered in blood yourself." Special Air Force trauma surgeons were called to help deal with the intensity of some of the wounds.

The horrific distinction of modern shootings is that they can be performed with automatic weaponry, which means that hospitals can be dealing with complex injuries and complications for months after the event. New York trauma doctor Dr. Robert Glatter told CBS News that "these automatic weapons cause devastating internal injuries. We may see an entry wound and an exit wound or may not even see the exit but it's internally that they wreak havoc. They can destroy the intestines, they can puncture the lungs, cause fractures, cause bleeding in the pelvis, and this is the unknown area where we have to use imaging tests and figure out exactly what's causing the bleeding."

UMC's chief of trauma surgery Douglas Fraser also noted that many of the injures from Sunday night involved "unusual patterns" because of the weaponry Paddock used. "These were quite large wounds that we saw," he told the Chicago Tribune. "The fractured shrapnel created a different pattern and really injured bone and soft tissue very readily. This was not a normal pattern of injuries." And gunshot wounds weren't the only injuries needing attention; others were coping with being trampled by stampeding people or wounds sustained while attempting to escape.

Complex, serious injuries may need multiple surgeries and require people to be in hospital for weeks or months, both while initial wounds stabilize and while ensuing issues like infection are managed. For the victims of the Las Vegas massacre, and the hospital staff dealing with the repercussions, the horror of Oct. 1 is far from over.