Standing before a class of Santa Rosa High School students, Mary Sega took a deep, trembling breath and then described the moment she watched paramedics pronounce her daughter dead.

Once a gregarious student who played football and baked cupcakes, Hope Sega, 18, had fallen unconscious after inhaling a quick hit of nitrous oxide from a whipped-cream dispenser, her mother told the students.

The teen lay lifeless on the ground, surrounded by strewn canisters, whipped-cream dispensers and boxes of cough medication, evidence of what her family had hoped was just a phase of experimentation.

"To me, this looks like a decorated crack pipe," said Mary Sega, holding up a whipped-cream dispenser painted pink and embellished with green feathers. "This is something she told me she was never going to do."

Hope Sega died March 17, five days before her 19th birthday, in a field off Dutton Avenue in Santa Rosa. She was partying with friends in a homeless camp, less than a mile from her family's home.

Since her daughter's death, Sega has launched a campaign to raise awareness about the dangers of using household items to get high, telling her family's story in a series of talks with students and parents to warn them about the dangers of inhalants.

"As soon as I saw all this stuff I began picking all this up," the 51-year-old Santa Rosa woman told a classroom of students, holding up boxes and canisters she found at the site where her daughter died. "I know this girl didn't know she would die."

Just one inhaled "huff" of nitrous oxide can send the brain into a state of euphoria, a seconds-long high that's gone almost as quickly as it hits the body. Many users ingest the substance again and again to keep the high going.

Yet each use — even the first — comes with a deadly risk.

"It's like jumping off that 20-foot cliff and there's that rock below the surface," said Dr. Gary Mishkin, an emergency-room physician at Santa Rosa Memorial Hospital. "Somebody is going to hit that rock."

Inhalants are a broad category of substances typically breathed in for a mind-altering effect.

Aerosols, gasses, nitrates and other volatile substances can be found in everyday items, from whipped-cream canisters and pressurized computer-keyboard cleaners to gasoline and paint thinners.

One of Hope Sega's last acts was to take a hit of nitrous oxide from a whipped-cream canister, said her mother, who spoke to several friends who were with her at the time. She earlier also had taken cough medication.

Eight months after Hope Sega died, Sonoma County coroner's officials have not issued an official cause of death. At the time, investigators noted evidence the teen and her friends had been inhaling chemicals from pressurized cans.

While alcohol and marijuana are the most common substances abused among local teens and adults alike, many of the students in Terry Swehla's health class nodded when Mary Sega asked if they knew people who had abused inhalants.

The students suggested Mary Sega talk to classes with younger students — fifth grade — who are on the cusp of experimentation.

Inhalants are "widely known as adolescent drugs," said Mike Maritzen, an addiction specialist and chemical dependency counselor with the behavioral health division of Sonoma County's Department of Health Services.

Among Sonoma County students, 13 percent of 11th-graders, 16 percent of ninth-graders and 9 percent of seventh-graders reported using inhalants at least once, according to the 2008-2010 Healthy Kids Survey.

Five percent of 11th-graders in the county said they had used an inhalant within the past 30 days — compared to 43percent who said they had used alcohol and 30 percent who reported using marijuana within the past month.

Inhalant abuse was greatest among students at nontraditional schools. Twelve percent said they had used inhalants within the past month and 31 percent said they had abused the substances at least once during their lifetime.

With fleeting effects, inhalants can become highly addictive when used over and over, Maritzen said. And impulse control is more of a challenge for adolescents because the frontal lobe of their brains has not fully developed.

Maritzen currently works with adults but for years worked with juveniles dealing with addiction.

"Working in adolescent treatment, I'd catch kids trying to huff felt pens," Maritzen said. "I could find three inhalants in any room."

Household chemicals and medications are the easiest items for young adolescents to access, he said.

"Start education early, after age 12 and up," Maritzen said. "It's not a popular subject when you talk to your kids. It's awkward, but it's important."

Lack of coordination and motor control, depression, memory problems and permanent brain damage are among potential side effects of long-term and sometimes even short-term use, said Jamie Ringheimer, an outpatient manager at Drug Abuse Alternatives Center, or DAAC, in Santa Rosa.

"People don't think they're as dangerous because they're over the counter," Ringheimer said. "It's not an illicit substance; it's nothing you have to buy on the street."

Ringheimer spoke of a client who had become addicted to using the pressurized computer keyboard cleaner Dust-Off and suffered side effects, including slurred speech, that made her appear drunk even when sober.

"With inhalants, it's a crapshoot. You never know what that huff is going to do," Ringheimer said.

Inhalant abuse doesn't come up every day at Memorial Hospital's emergency room, but it's not rare either, Mishkin said.

"I think this is very, very underreported, probably more than almost anything," Mishkin said.

Mishkin has worked as an emergency-room physician for about 25 years. But his education about the dangers of inhalants began as a junior-high student growing up in the San Fernando Valley when his close friend's brother died after inhaling Pam cooking spray.

"It was his first-ever time," Mishkin said. "He just went in the kitchen, he huffed it and dropped dead. He was 15 or 16 years old."

Chemical compounds in spray cans are volatile by design to propel outward. When inhaled, they can instantaneously cover all surfaces of the lung.

"They take away all oxygen instantly and enter the blood stream instantly," he said.

The body's reaction is unpredictable.

The pressure can puncture a lung. The chemicals can provoke an allergic-type reaction inflaming the lungs. Or they can suddenly knock a user's heartbeat into a fatally irregular rhythm.

"Think of a pitcher who got struck by a fast ball that knocked him dead," Mishkin said. "There are immediate risks that every user, every single time, is facing, including the first time."

About a month before Hope Sega died, she inexplicably quit her job behind the deli counter at Oliver's Market and announced she would be living in a tent with her boyfriend. Because her daughter had already graduated from high school and was technically an adult, Mary Sega said there wasn't a lot she and her husband could do other than try to talk her out of it.

In front of the class at Santa Rosa High School, the mother told the group she now believes that was the start of a downward spiral of experimentation.

"Maybe if you know this story from top to bottom you will make better choices," Sega said.

At the camp, Hope Sega started using inhalants like Dust-Off and whipped cream, according to her daughter's friends, Mary Sega said.

"I am told it is an out-of-body high, which is close to death and then you come back. But Hope didn't come back," she said.

A person with Hope Sega when she fell unconscious immediately called the teen's mother, who ran to the scene.

When she got there, she saw paramedics pounding on her daughter's chest and administering aid.

After about 30 minutes, paramedics stood back from her daughter.

"They told me, 'She's not coming back,'" Sega, wiping her eyes, told the students who sat wide-eyed and silent. "Her boyfriend was screaming. Her shirt was open, tubes were coming out of her body. Her eyes wouldn't close."

Sega held a box with her daughter's ashes at the front of the classroom while the students wrote questions and messages on pieces of paper and passed them to the front of the room.

Mary Sega read each one aloud.

"Your message is humbling. So many times I feel invincible, I need to remind myself life is precious," one student wrote.

Another penned: "I'm so sorry for your loss. I have a lot of friends who do them. I will tell them your story."

For more information about Mary Sega's efforts to raise awareness about household and over-the-counter substance abuse, visit http://hopenowdeclares.com.

You can reach Staff Writer Julie Johnson at 521-5220 or julie.johnson@pressdemocrat.com. On Twitter @jjpressdem.