Early-life exposure to anesthesia does not appear to lead to long-term cognitive problems, researchers announced today. New evidence from the first, randomized anesthesia trial in kids provides the strongest indication yet that exposing young children to anesthesia—at least for a brief time—will not saddle them with developmental deficits. The news comes just a couple of weeks after a medical advisory group reiterated its concerns about such exposures among children younger than four years. Previously, multiple animal and human studies have linked such exposure with cognitive impairment, but none of the information on humans came from a gold-standard, randomized study design that could help eliminate other reasons to explain such a connection.

This is a “reassuring finding, but it is not the final answer,” says Dean Andropoulos, anesthesiologist in chief at Texas Children’s Hospital and an expert who was not involved in the work. The new study assesses only what happens to youngsters after a relatively brief bout with anesthetics, so it is possible that longer or repeated exposures to such chemicals may still cause neurodevelopmental issues. There may also be deficits in anesthesia-exposed children that are not measurable until later in life.

The study followed more than 500 infants undergoing hernia repair across the U.S., Australia, the U.K., Canada, the Netherlands, New Zealand and Italy. The surgeries lasted an average of roughly an hour. About half of the children were randomly selected to be put under with general anesthesia, and the other half stayed awake during the surgery and received targeted anesthesic in a specific body region. The kids in the study were all younger than 60 weeks and were matched by where they had the surgery and whether they were born prematurely.

At age two, the children in both groups completed a battery of neurocognitive tests that examined how they thought and reacted to the world around them. The researchers found that the kids in both groups performed similarly. “This is the strongest evidence we have to date that a brief anesthetic exposure likely isn’t a problem,” says Andrew Davidson, leader of the investigation and director of the Melbourne Children’s Trials Center at the Murdoch Children's Research Institute.

The findings were published October 24 in the Lancet and will be presented Sunday at the American Society of Anesthesiologists annual meeting in San Diego. In recent weeks a medical group concerned about exposing young children to anesthesia, which includes the American Academy of Pediatrics and the U.S. Food and Drug Administration, cited the growing body of literature linking anesthesia exposure and neurodevelopmental issues to emphasize that although parents should not hold off on medically necessary surgery, they should always weigh the pros and cons of exposing a young child to anesthesia or sedatives. Numerous animal studies have indicated that anesthesia exposure early in life, when the brain is exceptionally sensitive, can lead to brain cell death and altered connections between neurons. The group also urged medical providers and parents to try to avoid using anesthetics during diagnostic procedures such as MRIs whenever possible.

Many of the surgeries performed on young children are short, similar to the ones in the experiment, but there are still unanswered questions about how these brief exposures to anesthesia may influence brain function later in life. To test if there may be harm from short exposures, those in the current study will also be reassessed at age five with a new spate of memory and cognitive tests that could pick up subtler differences that may not have been apparent at a young age, Davidson says. “There are some aspects of development—like high executive function, reasoning skills and memory—that you don’t actually acquire until you are older.”

Although most kids are generally healthy and do not require early-life surgeries or diagnostic procedures, in total at least half a million children younger than three years are exposed to anesthetic agents annually. There are several ongoing studies examining the long-term neurocognitive effects of such experiences. Meanwhile researchers are also looking into possible alternative anesthetics and ways to mitigate any anesthesia-related neurological damage.

Scientists are also trying to determine how to assess any real-world implications of a child’s potential anesthesia-linked neurological deficits. Testing a few points worse on IQ tests or other cognitive measurements may not substantially change a child’s daily life. But developmental experts have worried about how those deficits could stack up if they are common among many kids exposed to early anesthesia.

Until now, findings from observational studies of kids who had early-life surgeries have been mixed. They could not definitively answer if the anesthesia itself harms the brain or if some other underlying issues were at work—such as sicker kids need surgery and go on to have cognitive issues fueled by their illness. This new study, at least, helps to answer that question.