LAS VEGAS (Reuters) - From the field of sudden mass casualties to the unmistakable and devastating internal injuries of high-velocity gunfire, Sunday’s shooting at a Las Vegas music festival bore the hallmarks of war. So did the medical response.

FILE PHOTO: Medical bays are shown inside the Trauma center at the University Medical Center in Las Vegas, Nevada, U.S., October 3, 2017. REUTERS/Mike Blake/File Photo

The life-saving effort was in many ways textbook battlefield medicine.

It called on U.S. worst-case drills informed by lessons in wars from Vietnam to Iraq and refined by attacks on civilians in Paris, San Bernardino and Orlando.

And because the shooting occurred in a compact city with a fleet of ambulances and two trauma centers a few minutes away, the effort made the most of what doctors know as the “golden hour,” medical shorthand for a stark truth: Time is the enemy of the critically wounded.

Such care at close range saved lives, a success that would be harder to achieve in more isolated parts of the country, medical experts said.

“Vegas did it impeccably,” said Ian Weston, executive director of the American Trauma Society. “They practiced. They were ready.”

The fusillade the gunman poured on crowds at the outdoor festival from a 32nd-floor hotel suite killed 58 people and wounded hundreds of others - the worst mass shooting in modern U.S. history. Of more than 300 wounded who got to the city’s two trauma units, all but 20 survived.

Each less than a six-mile (10-km) drive from the shooting site, University Medical Center and Sunrise Hospital operate, respectively, Level 1 and Level 2 trauma units, the highest designations for such care reflecting the readiness and range of capabilities.

U.S. trauma care, a network of public and privately operated first response crews and medical centers, developed after World War Two around the goal of delivering patients at risk of bleeding to death to surgeons within 60 minutes.

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Today, more than 90 percent of the U.S. population of around 325 million lives within 60 minutes of one of the country’s roughly 2,000 designated trauma centers, broad coverage made possible by the reach of helicopter ambulances, which have limited capacity, according to the American Trauma Society.

The portion of Americans able to get to a trauma center within that time by ground transportation was only 64 percent in 2010 and probably has not changed much, Weston said.

That leaves almost 40 percent of the population, tens of millions of people, unable to get to a trauma center within an hour by ground transportation. Most of what trauma specialists refer to as the uncovered population lives in the rural West, including parts of Nevada, Idaho, Oregon, the Dakotas, Montana, Arizona and New Mexico, Weston said.

Several mass casualty events in the United States since the Sept. 11, 2001 attacks on New York and Washington have demonstrated that robust trauma care makes a difference.

After the bombing of the 2013 marathon in Boston, a metropolitan area with six Level 1 and 2 trauma units, all victims who got to hospitals were expected to survive.

“An urban center is going to be able to marshal resources,” said Dr. Mark Morocco, emergency medicine professor at the University of California, Los Angeles. “But outside the major cities, where you don’t have those resources, then you really are at risk.”

If something like the Las Vegas shooting occurred in an uncovered rural zone, say at a rodeo or a Friday night football game, trauma experts said the toll would likely be higher.

“A lot more people would be dead,” said Dr. Scott A. Scherr, emergency room director at Sunrise in Las Vegas.

LUCKY TO BE ALIVE

When Braden Matejka arrived with a bullet wound to the back of the head, he was swarmed by Scherr’s team and whisked to surgery.

“I was lucky,” said the country music fan from British Columbia, walking out of the hospital a couple of days later.

Scherr’s team organized incoming patients with color coded tags: from green for the walking wounded to red for those closest to death. Except for drills, it was the only time the hospital had deployed the tags, long used to sort wounded on battlefields.

At UMC Trauma Center, “patients were stacked everywhere” within an hour of the shooting, and were sent into surgery according to “who’s dying fastest,” said supervising surgeon Dr. Jay Coates. At one point, eight patients were in surgery simultaneously.

The surgeons and nurses there used skills they drilled a year earlier in a mock mass shooting similar to the November 2015 Paris attack on a concert hall and cafes in which 130 people were killed and hundreds of people were wounded.

In coming months, trauma teams across the country will study the Las Vegas response, drill what worked and avoid what did not.

National ambulance company AMR flooded the zone in Las Vegas, applying lessons its corporate counterparts had learned responding to mass shootings in Orlando, Florida; Aurora, Colorado; and San Bernardino, California.

In all, the service made 200 runs, helping turn the golden hour “into the golden 15 minutes,” said Damon Schilling, a paramedic and AMR manager.

When the first call was 20 people shot, “We said, okay, we’re sending 30 ambulances,” Schilling recalled. “When they said 40, we sent 50. And when they said more, we sent 106 ambulances.”