On Oct. 1, Toni Mullan drove 110 mph on side streets from home to get back to University Medical Center of Southern Nevada, where she’d just worked a 12-hour shift as a clinical supervisor in the trauma resuscitation department. Her car was smoking as she pulled into a three-hour parking spot close to the trauma center. Mullan, 54, left her hazard lights blinking as she shut the car door and raced inside.

Around a dozen patients had already arrived from the shooting scene at a music festival on the Las Vegas Strip. Two were dead and two had been “black tagged” — fully assessed and found to have injuries that were not survivable. Mullan’s daughter, Antoinette, 29, a trauma nurse who also works at the hospital, was standing out front with a physician assistant, taking injured patients out of vehicles as they drove up to the hospital and quickly assessing whose conditions were the most precarious.

By daybreak 104 patients had arrived, and more were expected as people were transferred from neighboring hospitals with fewer capabilities.

“The minute I got there, I looked at the situation and said, ‘How am I going to utilize my resources?’” the elder Mullan, a registered nurse, said in a telephone interview today.

University Medical Center is the only level-one trauma center in Nevada and one of only a few free-standing trauma units in the nation. That means it is fully staffed with surgeons and trauma nurses day and night to handle injuries and mass casualties, from vehicle crashes that bring in 10 patients at a time to a 2015 episode in which a woman drove onto the Las Vegas Strip, sending 17 patients to the medical center. Last week, there had been 15 trauma cases in one night.

But even with 11 trauma bays, three operating rooms, a CT scanner, a trauma intensive care unit and a pediatric intensive care unit all under one roof, the trauma center had never faced a torrent like this. For two or three hours, the patients came nonstop. The radio at the clerk’s desk blared with transmissions from paramedics. With the frequency overburdened, other paramedics resorted to calling in patients by phone. Many patients simply arrived unannounced in cars or, in one instance, several in the back of a truck.

To an outsider, “it would look like a disaster zone, a chaotic scene, very chaotic,” Mullan said. “If a nonmedical person were to be sitting there watching this, they would think nothing was being accomplished.”

But in fact much was being done. It had been a busy day, which meant some of the day shift was still present and stayed to work alongside the night shift. Pagers went off with a be-beep be-beep each time a severe trauma case was identified. Patients, most of them with gunshot wounds, were doubled up two stretchers to a trauma bay. At one point, beepers screeched as five trauma cases were clocked in at the same time. “We couldn’t hear each other talk, it was that crazy,” Mullan said.

The injured also poured into other area hospitals. Ambulances called ahead with the conditions of patients as they sped to Dignity Health-St. Rose Dominican. The hospital received 56 patients at its three campuses, 31 of them to the Siena location, a level-three trauma center. “No one has experienced patient volumes to this level,” said Jennifer Cooper, a spokeswoman.

As of Monday morning, four of those patients were in critical condition, one was still in surgery, and at least 21 had been discharged. None had died. Most had endured gunshot wounds, but others had been trampled while fleeing, or had been hurt climbing fences to escape the shootings.

Doctors and other staff members learned about the attack on the news and reported for duty on their own. Chaplains at the faith-based hospital offered spiritual care.

Phones in the emergency departments rang repeatedly with calls from family members desperate to locate and know the status of their loved ones.

“A lot of people still at that time were unknown as to where they were,” Cooper said. The Las Vegas Metropolitan Police Department established a list of victims at various area hospitals.

At the trauma center at University Medical Center, transport workers rolled gurneys and wheelchairs outside so they’d be ready as new patients arrived and wouldn’t take up space inside — a lesson Mullan said came from a recent training session with a doctor who had served after the Orlando Pulse nightclub shooting. Still, patients kept filling the trauma center.

“We had them in the hallway, we had them everywhere,” Mullan said. “Wherever we could find a spot we did.”

The next step was to open up more locations to receive them — a recovery room, a preoperative area, and an ambulatory surgery center were staffed and made ready. A separate place was set aside for the patients with unsurvivable injuries to receive comfort care until they died. Two areas were established for the “walking wounded” — patients with non-life-threatening injuries. With staff and volunteers pouring in, these patients, too, received immediate care from a dedicated doctor. An extra CT scanner was made available.

Teams combed through the patients, moving those who could be taken out of the intensive care unit to make room for others. Workers from the hospital’s central supply depot and linen department came up to check what was needed.

The trauma center repeatedly ran out of supplies including IV tubing and fluids, chest tubes, blood pressure cuffs, urinals and blankets, and “begged, borrowed and stole” them from other departments of the hospital.

The cafeteria was turned into a respite area for families searching for loved ones. Many patients arrived at the hospital and others as unidentified “Does,” lacking identification or cellphones. Mullen said as of Monday morning that the list of which patients were where was “still a work in progress.”

In the end, Mullan said, the systems in place were able to flex with the extra burden and bring care to all the patients who needed it. In the midst of the disaster, the trauma center even took in a burn victim and a pedestrian hit by a motor vehicle.

What served the hospital best was that it responded to emergencies every day. For other hospitals that may be called on in future mass shootings, Mullan had advice.

“Be prepared, be prepared and practice,” she said.

As she remained at the hospital late Monday morning, Mullan reflected on all the people who arrived to help, including workers who were not on shift and every hospital administrator.

“I’ve been a nurse for 30 years, and this was by far the worst moment I’ve had, the worst injuries,” she said. “But it was the proudest moment.”