THURSDAY, Feb. 2 (HealthDay News) -- Children who have more than one surgery with general anesthesia by their second birthday might be at higher risk for attention-deficit/hyperactivity disorder (ADHD), a new study suggests.

Mayo Clinic researchers looked through medical records of 341 children diagnosed with ADHD before age 19, to find who had undergone a surgical procedure with anesthesia before they were 2.

Nearly 18 percent of children exposed twice or more eventually developed ADHD. Children with only one exposure had an ADHD rate of nearly 11 percent, while never-exposed children had a rate of slightly more than 7 percent.

The researchers also looked at anesthesia given to mothers during childbirth.

"With Cesarean section with a general anesthetic, only a single anesthetic, we didn't find any effect," said study author Dr. Juraj Sprung, a professor of anesthesiology at the Mayo Clinic.

The study appears in the Feb. 2 issue of the journal Mayo Clinic Proceedings.

An earlier study conducted by the same team and published in Pediatrics last November found a connection between early multiple anesthesia exposures and a higher rate of learning disabilities in reading, language and math.

Data for both studies came from the Rochester Epidemiology Project, which analyzed education records of children born between 1976 and 1982 in Minnesota.

Nearly one in 10 children is estimated to have ADHD, which hampers attention and focus, and includes restless and impulsive behavior. Studies suggest that both genetic and environmental factors play a part in causing the neurodevelopmental disorder.

For human studies, it's difficult to separate the effects of anesthesia from those of surgery. "Essentially, we did an observational study and we examined whether there is association with exposure to anesthesia, but not only to anesthesia," Sprung said.

In earlier animal studies, rats given anesthesia developed nerve damage in the cortical areas of the brain and became hyperactive. Newborn monkeys exposed to the anesthetic ketamine for 24 hours had changes in their ability to perform tasks involving executive function.

While she was struck by the animal data, Dr. Tanya Froehlich, a specialist in developmental and behavioral pediatrics at Cincinnati Children's Hospital Medical Center, said the new study does not prove a cause-and-effect connection between surgical anesthesia and ADHD.

Any link "could be confounded by a lot of things," she said. "For instance, kids with ADHD are more prone to injury. They're more prone to breaking their bones, possibly having some kind of head trauma that might require surgery. A child who's under 2 is prone to being more active, getting into things, so they might have a propensity to have more accidents."

With ADHD's familial component, she said, it might also be that caregivers are more likely to have the condition themselves and "may be less adept at keeping track of what the kids are doing and putting those safety precautions in place."

Or, a child's surgery could be for a congenital malformation that itself may have affected the brain and increased the ADHD risk. "And it doesn't necessarily have to be the surgery or anesthesia per se," Froehlich said.

"When I read the study, I thought of a lot of reasons that anesthesia and ADHD may be associated but not necessarily causative. In the study they're only proving an association," she said.

The findings may not apply to children of all racial or ethnic groups, Sprung added. "The population in 1976 and 1982 was mostly white/Caucasian here in Minnesota."

However, Froehlich said, "the dataset that the Minnesota people have is a huge strength. Notably, they did account for birth weight, gestational age and maternal education in their analyses, so that all speaks very well for the study and strengths of the study."

Both experts stressed that parents should not avoid needed surgery for their young children.

"At the present time, we shouldn't make any recommendations based on the study, to do or don't do the surgery. If you need the surgery, if you need the procedure, you certainly should go for it," Sprung said. "What I would personally say: If it's the type of surgery, the type of procedure that can wait, maybe it's better to wait."

And Froehlich said, "Even though we can think of all these confounders we can't just dismiss the study. It's something that we as doctors should be aware of and should think about."

More information

Visit Nemours to learn about what to expect when children undergo anesthesia.