Researchers at Washington University School of Medicine say fears that nitrous oxide raises the risk of heart attacks during or soon after surgery are unfounded.

Their findings will be published in the July issue of Anesthesiology.

The theory was based on the fact that nitrous oxide — often called laughing gas — inactivates vitamin B12 and thereby increases blood levels of the amino acid homocysteine, which has been associated with greater cardiac risk.

To test the theory, the researchers followed 500 patients at Barnes-Jewish Hospital in St. Louis who'd been diagnosed with various heart problems. Half were given B12 and folic acid intravenously during surgery to help keep homocysteine levels from rising. The other half were not.

The vitamins kept the levels from rising, "but that didn't influence heart attack risk," says lead author Dr. Peter Nagele.

To detect heart attacks, the researchers monitored cardiac troponin I, a heart damage marker, for 72 hours. They found no link between the marker and homocysteine.

Jim Burger