(Reuters Health) - In infants, an hour of general anesthesia - long enough for most minor surgeries done in babies - doesn’t increase the risk of impaired brain development compared to an hour of regional anesthesia, a study suggests.

By age three, roughly one in 10 children in developed countries will have had general anesthesia at least once for things like repairing a hernia, placing ear tubes, removing tonsils or completing MRIs, researchers note in The Lancet.

Parents sometimes try to delay these interventions until children are older, out of concern that general anesthesia may impair brain development in kids. But research to date on this connection has yielded mixed results and relied primarily on animal studies.

For the current analysis, researchers randomly assigned 722 infants in seven countries undergoing hernia repair surgery to receive either general anesthesia or a spinal block, a type of regional anesthesia. Kids who had general anesthesia were unconscious for an average of 54 minutes.

At age five, the kids had similar test scores from assessments of IQ, attention, memory, executive function and behavior, regardless of which anesthesia they had, the study found.

“The trial finds the strongest evidence to date that an hour of anesthesia does not increase risk of later cognitive or most other neurodevelopmental problems,” said senior study author Dr. Andrew Davidson of Royal Children’s Hospital and the Murdoch Children’s Research Institute in Melbourne, Australia.

“There are some aspects of neurodevelopment that manifest later in life and the trial does not address, these however the results at five years of age are very reassuring,” Davidson said by email.

It’s unclear what would happen with longer surgeries, Davidson added.

“We cannot conclude that longer exposures are safe, however the majority of anesthetics in children are under an hour,” Davidson said.

The results offer some of the strongest evidence to date that parents don’t need to delay surgical procedures for infants and toddlers out of concern that general anesthesia might harm their developing brains, the researchers conclude.

Surgeries in this study were done between 2007 and 2013. A previous analysis of interim results in 2016 found no difference in neurodevelopmental outcomes at age two with general versus regional anesthesia.

Previous studies of anesthesia risks for young kids haven’t been controlled experiments designed to prove whether or how anesthesia might cause physical or mental health problems, the study authors note. While the current analysis was a controlled experiment designed to answer this question, it wasn’t without its own flaws.

One limitation is that most patients were male, making it unclear if results would be the same for female patients, the study authors note.

In addition, many children dropped out of the study and several kids who were randomly selected to receive regional anesthesia actually needed general anesthesia during their procedures. This reduced the total children in the final analysis to 205 kids who had regional anesthesia and 242 who received general anesthesia.

“It is still not known whether children with repeated or lengthy exposures to anesthesia are at increased risk of adverse outcomes, and there may be other subgroups of children with increased vulnerability to anesthesia-related neurological injury,” said Dr. James O’Leary of the University of Toronto in Canada.

However, “from the results of this study and others, parents of children requiring surgery should be cautioned about delaying necessary surgery because of concerns over anesthesia neurotoxicity,” O’Leary, author of an accompanying editorial, said by email.

SOURCE: bit.ly/2EhJ4AE The Lancet, online February 14, 2019.