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SAN DIEGO -- Note to backcountry skiers: You can now carry an airbag with you as a protection against the ever-present danger of an avalanche. But these airbags aren't just in the business of cushioning your encounter with a wall of ice, a ski country emergency physician told colleagues this week. They're also designed to push your body toward the surface.

You can also bring along a unique breathing device on your ski run, and this may be especially crucial to your survival in an avalanche. "We know it's not trauma that kills most victims," said Scott E. McIntosh, MD, MPH, MACEP, of the University of Utah School of Medicine. "It's actually asphyxia. It's the number one killer."

McIntosh spoke about avalanche safety -- both from the skier's perspective and the rescuer's perspective -- at the annual scientific meeting of the American College of Emergency Physicians.

According to the National Avalanche Center, avalanches kill dozens of people in the U.S. each year. There were 29 avalanche fatalities in 2016 and 11 in 2015. The over the past 20 years.

In a 2007 study, McIntosh and colleagues analyzed 56 avalanche deaths in Utah from 1989-2006. Of the deaths, 86% were caused by asphyxiation, and the rest by trauma alone or trauma and asphyxiation.

In the trauma cases, he said, injury can come from the snow's tremendous weight and pressure on the body. In some cases, the diaphragm and esophagus is ripped apart. People who have survived avalanches say "it's like being tumbled in a big washing machine and there's no way to get out of it," he said.

Head and scalp injuries are also possible. Many skiers in backcountry areas do wear helmets, he said, "but helmets are only good if you use them properly."

Asphyxia occurs due to so-called "avalanche burial," McIntosh said. "You're having a problem with respiration and ventilation. Your chest is being crushed by that amount of snow, and every exhalation means more carbon dioxide is building up in that airspace."

Research has suggested that asphyxia deaths can occur quickly, he said, but there's a "curious plateau to from 40 minutes to hour" where deaths level off. In these cases, he said, it appears that avalanche victims survive in air pockets.

Backcountry skiers and snow hikers often carry beacons, probes (for finding victims), and shovels as defenses against avalanches. Some skiers use a breathing device that separates inhaled air from exhaled air, he said. It allows them to breathe in air from the surrounding snowpack and exhale to the space behind them. This device improves survivability, he said.

Two such breathing devices are available at REI for and .

"Avalanche airbags" are also available. Typically, they're U-shaped. They're triggered by a manual ripcord, McIntosh said, and can protect the head and neck.

That's not all. The airbags increase the body's volume and raise the body to a higher level through granular segregation, also known as the "Brazilian nut effect."

"If you have a can of mixed nuts and start to shake them up, the bigger nuts will tend to rise to the surface," he said. The airbags work under the same principle. for up to $1,250.

According to McIntosh, airbags lower avalanche mortality by half, to 11%.

As for treatment of avalanche victims, McIntosh said "rescue must be quick and efficient."

He recommended protecting the victim's face, airway, and thorax from snow. A core temperature probe can be helpful. "If they're warm, over 30°C, they're probably not sustaining a hypothermic problem or hypothermic arrest," he said.

McIntosh was recently reminded about the impact of a successful rescue.

In 2007, an 11-year-old boy was buried by an avalanche while skiing in Utah, and rescuers couldn't find his beacon for 39 minutes. Fortunately, he'd grown up in Park City, Utah, where "you hear a lot about backcountry safety," McIntosh said.

The boy had seen a safety video, so he knew to wave his arms when the avalanche slowed down in order to create an air pocket. "Two helicopters were dispatched, and the patient was intubated and flown to the local children's center," McIntosh recalled. "He did have a respiratory arrest while underneath the snow and was kept on ECMO [extracorporeal membrane oxidation] for 24 hours. Then he was ."

So well, in fact, that he just heard from the boy's mother, who had some good news: He just graduated from college.

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