Dr. David Warner hoped that a careful study would knock out the theory that anesthesia increases the risk of attention and learning problems in children.

So excuse the Mayo Clinic anesthesiologist if he wasn't thrilled with the results he reported Thursday: Children exposed repeatedly to anesthesia as infants and toddlers were more likely to have attention deficit-hyperactivity disorder (ADHD) as children.

"There does seem to be an association between these problems and exposure to multiple anesthetics," Warner said.

The correlation does not mean that anesthesia causes ADHD, he cautioned. Nor does it explain the vexing rise in childhood ADHD diagnoses. (A 2010 federal report concluded that parent-reported ADHD rose from 7.8 percent of all children in 2003 to 9.5 percent in 2007.) While diagnoses of the disorder have climbed, the rate of young children undergoing surgery has not changed much.

Warner's study monitored 5,357 children born between 1976 and 1982 in the Rochester area. Overall, 7.3 percent had ADHD by the time they reached age 19. Among those who received anesthesia two or more times by age 2, the incidence of ADHD was 17.9 percent.

It's possible that children who undergo multiple surgeries in their early years are unique -- and that repeated anesthesia exposure is just a "marker" for the real cause of ADHD. On the other hand, the link held up even when the study was weighted to account for other potential causes, such as low birth weight, prematurity or chronic ailments.

The children with ADHD and who were exposed to anesthesia weren't necessarily seriously ill, Warner said. Some had ordinary procedures as toddlers, such as having ear tubes implanted.

"We've done several things to try to make this [association] go away," said Warner, co-author of the study that is being published in the latest issue of Mayo Clinic Proceedings. "One is to just say these are really sick kids who have a lot of problems," but that turned out not to be the case.

The research was inspired by animal studies showing that mice exposed to anesthesia had learning and attention problems.

Warner said parents should not conclude that their children should avoid anesthesia. "The last thing we want to do is scare people away from necessary surgery when we publish findings like this," he said.

Jeremy Olson • 612-673-7744