Anesthesia could have long-term harmful effects on the developing brain, according to animal studies presented Thursday to U.S. regulators.

At U.S. Food and Drug Administration hearings, scientists stressed they have no evidence the drugs can cause brain damage in children.

The concerns were raised because exposure to anesthesia was linked to small amounts of brain damage and mild behavioural changes in lab animals, according to a study published by FDA scientists this month in the journal Anesthesia & Analgesia.

Experiments have shown that many of the anesthetics used on children kill brain cells in young rats and mice, as well as rhesus monkeys in preliminary tests.

"It is not clear at this time what this means for the clinical setting, or for children who undergo anesthesia, whether there are any effects at all, or whether any long-term effects," said Dr. Bob Rappaport of the FDA's division of anesthesia, analgesics and rheumatology, one of the authors of the study.

Concerns about memory loss and attention deficit disorder are so far unfounded, but more study is needed to take a closer look at the long-term effects in young patients, anesthesiologist Dr. Scott Kelley of Aspect Medical Systems told the meeting, which was called to inform experts about the research.

Not all drugs appeared to be equally harmful in animals, and different effects on the brain were found depending on the dose and duration. Some combinations of drugs appeared to be more toxic than when used individually.

Children under three may receive general anesthesia during surgeries for ear tubes, hernia repairs or stitching up serious wounds, said Dr. Dean Kurth, anesthesiologist-in-chief at Cincinnati Children's Hospital Medical Center.

Alternatives to anesthesia

In the U.S., two new studies will look at the long-term effects of anesthesia in adults, such as possible strokes, heart attacks and liver damage.

For now, there are few appropriate alternatives to current anesthetics.

It is important to find the correct level of anesthesia to prevent patients from waking up during surgery or feeling pain. For children in particular, too much anesthesia can cause patients to slip into a coma and die, not only during the surgery but also afterwards.

In 2004, the Canadian Institute for Health Information's fifth annual report on medical errors found anesthesia errors dropped during the previous decade. 

With files from the Associated Press