LAS VEGAS — Dr. Kevin Menes had prepared for this moment, when terror came to his city and his hospital, but once it arrived he couldn’t believe it was true.

A radio used to alert the hospital to incoming casualties was blaring. Menes strained to understand. He heard someone say, Prepare for a mass casualty incident.

“Hey, is this real?” Menes asked, turning to a police officer passing through the emergency room. Maybe it was another drill meant to look real, with fake blood and screaming actors. Or one more false alarm, one more night Sunrise Hospital prepared for a panic that never arrived.

“Yeah, man,” the officer replied.

Menes sprinted toward his car.

Menes, 40, chose to work the weekend night shifts in Sunrise Hospital’s emergency room because they offered the greatest opportunity to save a life, to see a person come into the hospital dead and leave it alive. He also volunteered as a medic with the Las Vegas Metropolitan Police Department’s SWAT team, and kept a police radio in his car.

In the parking garage, he listened in as officers swarmed the Strip.

Automatic fire, he heard them yell. Concert.

How many people did that mean? Fifty? A hundred? A thousand? There was no way to know.

Menes didn't know that six miles away, a gunman had shattered his hotel windows and opened fire on 22,000 fans at the outdoor Route 91 Harvest Festival. He couldn't know that almost 600 patients would flood into hospitals across the city — an unprecedented rush of gunshot wounds into American hospitals. Fifty-eight would die.

Menes sprinted back inside, where three other emergency doctors waited, and told them, “We’ve got to get ready.”

Secretaries started down the first branches of phone trees, calling whomever they could into the hospital. Nurses cleared the emergency room and threw open the curtains to trauma bays. A trauma surgeon pulled on scrubs in his office. Housekeepers rushed to find enough clean linens.

For years Menes had imagined these moments. Theirs was a city of crowds, of festivals and concerts and other targets of terrorism, and he wanted his response to be automatic. He quizzed his emergency response team and built plans in his mind. Friends at the hospital grew used to hearing him talk about mass casualties and trauma and triage.

Menes decided he would stand in front of the hospital, where the life-and-death decisions would be made. As a medical resident in Detroit he worked a Super Bowl, stationed in a room that would fill with victims if terrorists struck. He thought that was the most important place to be. But he learned that the most important position was at the front door. A doctor outside could filter through waves of patients and ensure a hospital’s resources went to the most critically injured.

Menes sent the other ER doctors to the diagnostic area, a group of half-rooms just behind the waiting room. The trauma surgeon, Dr. Dave MacIntyre, put crash carts in the trauma bays, four curtained-off areas that took up two walls in the ER.

Doctors in place, Menes found a secretary at the front desk and told her to call every surgeon and scrub tech she could find. “I need every operating room open,” Menes said. MacIntyre directed six surgical residents there to stand ready.

Hospital transporters brought every gurney and wheelchair they could find downstairs, and Menes pointed them outside, to the two curved drives that led to the ER’s sliding doors.

As preparations locked into place, the rumors of a mass shooting ricocheted through the hospital: At first there was one shooter, then two. They caught the shooter. The shooters got away. Nobody knew for sure.

“I’m worried somebody’s going to come here and start shooting at us,” Menes told a police officer. He knew terrorists sometimes moved to hospitals to cause the most damage.

“I’ve got you, Doc,” the cop replied. “We’ll get some officers over here.”

Soon a string of police cars arrived, drawing a flashing line between the chaos outside and the quiet inside.

Sunrise Hospital had five trauma doctors in the building and hundreds of patients on the way, piled into pickup trucks, ambulances and the backseats of police cruisers.

Menes turned to Debbie Bowerman, an emergency room nurse who had followed close behind. “Come on,” Menes said, leading Bowerman outside. “Let’s go.”

They walked through the sliding doors of the emergency room and sat on a gurney, listening as a wall of sirens drew closer.

♦ ♦ ♦

Sunrise Hospital’s staff often calls it “the busiest ER in Nevada.”

It takes the brunt of Vegas trauma: Gunshots, broken legs, constant cases of alcohol poisoning. Gang shootings and car crashes end up at Sunrise. Memories of the 2015 night a drunk driver plowed through dozens of people on a sidewalk linger.

More than 300 patients flow through its ER on an average day. Sometimes that number surges as high as 350, and Sunrise feels the swell.

On Oct. 1, that same ER treated 199 patients in six hours.

There was no way to prepare for the volume. Sunrise runs mass-casualty incident drills at least twice a year, but no hospital had ever taken in hundreds of gunshot victims at once. There was little time for procedure. There was only time to react.

Video: 'It was overwhelming'

The USA TODAY NETWORK pieced together that reaction in interviews with more than a dozen doctors, nurses, hospital administrators and other Sunrise staff in the days after the deadliest mass shooting in modern American history.

Sunrise brought more than 100 doctors and 200 other staff into the hospital after the shooting, clawing for more manpower and resources to keep up with the demand. Five chaplains stood by, hoping against the dismal ritual of death.

Then the sirens arrived, carrying their wounded.

The staff's collective attention shifted to the ER. Transporters pushed patients inside, where they met doctors and nurses carrying spare gloves and IV bags. Behind everybody trailed a squadron of Environmental Services staff, who ripped off bloodied bed sheets and mopped up trails of blood.

A hospital pharmacist unlocked the stock of drugs used to intubate patients. Nurses stuffed the medicine into the pockets of their scrubs, along with the blood bank’s entire supply of O-negative.

There was no time to build medical records or create charts, so doctors wrote notes directly on patients’ bodies. Patients who couldn’t tell a doctor their name took on a new identity. First names were assigned alphabetically, like hurricanes. All shared one last name, a silent family brought together by bullets.

Debbie Trauma: Female, gunshot wound to the chest.

Eddie Trauma: Male, gunshot wound to the head.

Freddie Trauma: Male, gunshot wound to the belly.

Six miles away

Rob Weiss and his wife, Beth, had looked forward to the Route 91 Harvest festival for months. They splurged on VIP tickets, and their teal wristbands ensured a good view and a place to sit. They preferred the young artists on the “Next from Nashville” stage, but when Jason Aldean took the main stage they found their seats in Zone A.

Aldean played his hits, one after another. Then the band slid into “When She Says Baby,” and the house lights dropped. Everything went dark. Weiss saw the band scramble for cover. People in the crowd started to fall.

Weiss, a physician assistant at Sunrise, recognized the crackling over his right shoulder as gunfire. He and his wife hid behind their seats, waiting for a moment to scurry down the steps. When one came, they worked their way to the ground.

“I need to get to the medical tent,” Weiss told Beth. But the tent was tucked into the opposite corner, across the festival grounds.

They sprinted through the crowd, weaving through the people pressing against the edges and trying not to look at those left behind, stopping only at the sound of bullets. Each time the shots started again, Weiss pushed his wife behind something solid and covered her body with his.

Four times the bullets returned. Four times he threw himself over her.

Inside the medical tent, Beth dug through medical supplies meant for sprained ankles and sunburns. Rob examined every person he could find.

Had they been shot? Where? Belly wounds were the worst, because they bled out the fastest. How critical were they? Did they need a hospital now, or could they wait a few minutes? Was there even any room in the hospitals?

Blood spattered across his T-shirt and shorts. He knelt to work in crimson pools, and it dripped down his legs.

Rob handed his phone to Beth, who texted his supervisors and asked how many people each hospital could take. There were no clear answers. A rumor spread that University Medical Center, the state’s only Level I trauma center, had closed its doors. That wasn’t true, but UMC cleared its ER for patients that never came.

So Weiss sent most critical patients, those with dilated pupils and a slow pulse, straight to Sunrise. He sent them in whatever vehicles he could find, working the tent until every person had left.

Then he checked back in with Sunrise. The staff was overwhelmed. He told them he was coming.

He had parked in Mandalay Bay, which wasn’t allowing cars to come or go. There was only one way out. Weiss and his wife climbed into the back of an empty ambulance, strapped themselves in and rode the empty streets to Sunrise.

'How many more?'

The wounded arrived in waves.

First came the police cruisers dropping off two at a time. Then the pickup trucks and two-door sedans, backseats stained with the blood of as many they could hold. Ambulances that abandoned protocol, bringing five at once, no time for backboards or stretchers. The walking wounded, staggering through the sliding doors.

“How many more can you take?” a commander from the Clark County Fire Department asked every few minutes.

“Ten more,” Director of Emergency Services Dorita Sondereker always told him.

Kevin Menes met each one outside the ER. He stood in the alley leading to the ambulance bays, bathed in flashing lights as he and Debbie Bowerman pulled people out of vehicles. They worked in a strange stillness, a quiet shock that filled the ambulance bays.

“Where are you shot?” Bowerman asked each patient. Menes felt for a pulse and looked into their eyes, assigning each a color based on how long they might live.

Green tags were people shot in the arm or leg, able to survive hours with water and pain medication. They sat on plastic chairs or on the floor, filling the crevices of an emergency room crammed full.

Yellow tags had been shot in the chest or torso and would die within an hour. Menes put them in curtained-off rooms next to the trauma bays. A squad of nurses waited for them, watching for any drop in vital signs.

Red tags had minutes to live. They were sent straight to the hospital’s four trauma bays.

And at least 10 patients emerged from their makeshift ambulances without a pulse.

Black tags.

Under the trauma system, people who die before reaching a hospital are given black tags and directed to the morgue, where they won’t take time or resources from patients who might still live. But Menes convinced himself every life could be saved, so he sent each one into the ER with a red tag.

Video: 'All hands on deck'

Dying patients are typically the smallest group in a mass-casualty incident, and Sunrise’s trauma bays were built to hold one red tag at a time. But patients kept coming. They kept crashing. Transporters slid patients into place like Tetris pieces, pushing as many as six together and capping them with gurneys at their head and feet.

“Make a path!” transporter Stephen Hooker yelled over the crowds, rushing patients through hallways lined with people who sat wherever they could find room.

“Am I going to die?” one patient asked him.

“Hey man,” Hooker replied, keeping his voice low, “you’re doing really good. Just keep breathing. The doctor’s going to come see you as soon as they can.”

Patients were scattered everywhere. Bleeding patients slumped in plastic chairs. They draped gunshot-riddled arms and legs over desks and tables as nurses reminded them to keep the wounds elevated.

A thick line of blood traced their movements. Blood on the walls. The metallic scent of blood in the air. Blood that clumped on shoes and fresh blood that made the floors slick.

Friends and family of victims crammed into the waiting room, taking up every chair and most of the floor space.

Thirty patients came. They’ll handle it, Menes told himself. He kept scattering them throughout the hospital. The number climbed higher and higher. He lost track.

“Menes!” somebody screamed. He spun around and saw a nurse standing just outside the sliding doors. “Get inside here, now! They’re falling behind!”

But the waves were still coming. His training told him to stay out front, but inside people were dying. He grabbed Bowerman by the shoulders.

“You’ve been watching what I’ve been doing, right?” he asked. Cars and gurneys streamed around them.

Bowerman nodded.

“I have to go. You got this?”

“Yeah,” she said. “Go inside.”

Menes changed his gloves and sprinted toward the trauma bays. All he saw was blood.

Into surgery

Dave MacIntyre, the trauma surgeon, knew his patients only by their red tag and their temporary identity. He filtered them further, grouping them by the location of their gunshots: Heads, chests and bellies.

A gunshot to the head kills 90 percent of its victims, but a bullet to the stomach can kill in minutes. MacIntyre, 51, placed a surgical resident in each of Sunrise’s six operating rooms and sent belly wounds there for damage-control surgery.

To completely repair one patient’s injury would be to let another bleed out, so Sunrise’s surgeons did the bare minimum: Find the hole, stop the bleeding, and seal the incision with a sponge. There was no time for staples or stitches.

Hospital secretaries called down the list of on-call and backup surgeons. They lit up the pagers of plastic surgeons and pediatric specialists, of orthopedic and ear, nose and throat surgeons. They called the chief of neurosurgery, Dr. Michael Seiff, who followed a police cruiser through the traffic.

MacIntyre stayed in the trauma bays to stabilize the other patients.

“What’s your name?” he asked each one. If a patient answered, MacIntyre propped them up and moved on.

Patients who didn’t answer, who either weren’t breathing or had suffered brain damage, were moved through Advanced Trauma Life Support, a fast-tracked system for stabilizing trauma patients.

MacIntyre intubated patients who weren’t breathing and connected them to a ventilator. Instead of inserting IVs, he used a bone-drilling machine called an intraosseous catheter, which injects drugs straight into the tibia. From there, medication flows through the blood-rich center of the bone and heads toward the heart.

Then he sent them to wait for an operating room: Chest injuries went to the cardiothoracic unit, and head injuries to the trauma intensive care unit. Surgeons were on their way.

♦ ♦ ♦

Dr. Keith Blum sped underneath red lights, listening for details over talk radio. He called his wife, who didn’t know much more. As the on-call neurosurgeon, a secretary reached him a few minutes after the shooting started, but he lived a half-hour’s drive from the hospital. The traffic made it longer.

“They’re all here,” MacIntyre told him as he walked in, pointing toward the trauma ICU where he had sent 10 patients shot in the head. Blum walked from patient to patient with a pen and a sheet of paper, checking each one for brain function and the holes in their skull.

Most mass shootings end with a small percentage of gunshots to the head. Shooters fire from the ground. Their bullets lodge into backs and buttocks as people flee.

This shooter fired from above, cratering rounds deep into the top of people’s skulls.

There was time for only the briefest of exams: Neurosurgeons leaned down to each patient’s bedside and shined a small flashlight into their eyes. If their pupils were fixed wide and black, there was little they could do. They dug a key underneath patients’ fingernails. They hooked a finger and jammed it into the notch of each patient’s eye socket, watching for a reaction to the pain.

Patients who reacted took priority in the operating rooms, where six neurosurgeons eventually scrubbed in. Blum operated on one patient, a 27-year-old woman who had been shot through the right eye. He removed the eye and parts of her skull. She survived.

In the ICU, Blum worked through the patients quickly. The ICU felt warmer than usual. He thought of his father, a veteran of World War II, Korea and Vietnam who leapt out of bed to fight invisible demons. He pictured the turmoil of the battlefield, the medics who sprinted between soldiers in their dying seconds.

We’re just dealing with one incident, at one time, he thought. They had been trained to toe the line between life and death, to make the cold analysis of who could be saved and who was already gone. But no hospital could train for this.

♦ ♦ ♦

Trauma medicine relies on a concept called the Golden Hour. If a critically wounded person can get to the hospital and into an operating room within an hour, their chances for survival spike. After the first hour, injuries worsen and patients start to crash.

The Golden Hour had passed when Menes ran into the ER. He had pushed more than 50 red tags to MacIntyre, but now his yellow tags were fading to orange.

He considered himself a “rescuscitologist,” a specific breed of doctor who found dying people and brought them back. He couldn’t remove bullets. He couldn’t repair holes in skulls or organs. All he could do was keep people alive until they reached the top of a surgeon’s list.

"This one’s going down!” a nurse screamed, and Menes launched into the unsteady routine of trauma: Intubate, insert a chest tube, push blood. The patient stabilized, and Menes scanned the room, searching for the patients closest to death.

Gallery: Las Vegas shooting victims

Two young girls, both shot in the neck. A man with bullet holes in his back and chest, straight through a tattoo. One green tag who stopped breathing. Menes stabilized them in bunches, changing gloves after every patient. At one point, he found himself pressed back-to-back with two other doctors, three men intubating three patients in a trauma bay built for one.

“Menes!” somebody yelled. He spun around and saw Bowerman atop a gurney, rolling down the hallway as she knelt over a woman’s body. The young woman had been shot in the head, and when Bowerman pulled her out of a vehicle she felt no pulse.

Menes hurried into the hallway to examine the woman. Blood matted her hair and her plaid shirt, still tied at the waist. Her face was pale, her skin cool.

She was gone.

It was time to stop, Menes told Bowerman. Not everybody could be saved.

Bowerman left the woman and walked back outside. More patients were arriving.

The ambulance dropped Rob Weiss at Sunrise just before midnight. He pulled Beth through the mass of people and directed her into a small office by the ER’s front desk. He promised to check on her as often as possible and ran to the ER, working on patients who saw his teal wristband and knew he had been there with them.

Gallery: Las Vegas shooting

Into the morning

On and on Sunrise went, intubating and stabilizing until 4 a.m., after a city of lights had fallen asleep in darkness.

Finally, the emergency room started to slow. The red tags had been shuffled in and out of surgery. Almost every yellow tag had been stabilized. The morning shift of ER doctors started to arrive, treating the green tags that remained.

Housekeepers swept through the emergency room, collecting debris and replacing linens. They mixed buckets of chemicals and pushed their green mops along the hallways, cleaning streaks of blood.

Sixteen people were declared dead at Sunrise. Hospital staff gathered the bodies near the operating room, because the morgue couldn't hold them all.

Hundreds of people started to filter out of the hospital. Weiss found his wife, still in that tiny office, and they took a Lyft home. Blum drove himself home in silence. Tears blurred his vision.

Bowerman sat at the ambulance window for the last few hours of her shift. MacIntyre scrubbed in and operated on two patients with belly wounds. When he finally went home, the guilt of leaving almost sent him back.

Menes stayed in the ER, taking remaining patients to CAT scans. Around 5 a.m., Menes opened one more set of results. The words blurred together. He put an eyedrop in each eye and tried again. Still, he couldn’t read anything.

It had been seven hours since a man opened fire on an unsuspecting concert crowd. Menes had triaged 199 patients and stabilized more than he could number.

I can’t believe we moved that many people, Menes thought.

He walked out of the now-empty emergency room and through the parking lot that had been full just a few hours earlier. He drove toward the Strip, where the SWAT team had set up a command post by Mandalay Bay. There was no need for a medic, the officers told him, and finally he pointed the car toward home.

As he turned down Las Vegas Boulevard, away from Mandalay Bay and the concert stage, the city’s famed Welcome to Fabulous Las Vegas sign came into view. There was no crowd, no line of people waiting to take a picture. Nobody had yet thought to bring candles or flowers.

Menes parked his car in the empty parking lot. The gold towers of Mandalay Bay rose behind the sign. He stepped onto the artificial turf and took a photo of himself.

Las Vegas had never been so quiet, and he wanted to remember the feeling.