Experts have expressed concern that laughing gas, scientifically known as nitrous oxide, can raise the risk of heart attacks when the drug is given as part of anesthesia, during or after surgery. However, a new study found it doesn't increase the risk, giving people undergoing surgery one less thing to worry about.

"It's been known for quite a while that laughing gas inactivates vitamin B12 and, by doing so, increases blood levels of the amino acid homocysteine," Peter Nagele, assistant professor of anesthesiology and genetics, and lead author of the study, said in a press release. "That was thought to raise the risk of heart attack during and after surgery, but we found no evidence of that in this study."

The American Heart Association says that high levels of homocysteine have, in past studies, been connected to a higher risk of coronary heart disease, stroke, and peripheral vascular disease. Evidence also suggests that high levels of the amino acid can lead to fatty deposits in blood vessel, which in turn can case damage in the inner linings of arteries, and facilitate blood clots. These are all symptoms that can lead to a heart attack.

However, in the recent study undertaken at the Washington University School of Medicine in St. Louis, researchers studied 500 patients who had been diagnosed with coronary artery disease, heart failure, or other health problems. They all underwent surgery and received nitrous oxide anesthesia — all surgeries were unrelated to the heart. But some of the patients underwent surgery while receiving intravenous B12 and folic acid to combat the low levels induced by the laughing gas, while the others didn't.

In addition to this, the researchers also looked into gene variants that could increase homocysteine levels. They knew that people with variants of the MTHFR gene already had higher levels than usual, and were interested in whether their levels went even higher under anesthesia.

For 72 hours they monitored the patients, looking for a rise in troponin levels, which would've indicated heart damage. But they didn't find anything. Although the B12 and folic acid kept homocysteine levels down during and after surgery, neither groups showed risk for heart attack beyond what they had before surgery.

What's more, they found that only 3.1 percent of the patients with the genetic variants had heart attacks during or after surgery, compared to 4.7 percent of the patients without the variants.

"People who had the gene variant did, indeed, develop very high levels of homocysteine in response to nitrous oxide," Nagele said. "So the question is whether those patients would be at higher risk for heart attack, and that answer is no."

This study gives patients undergoing surgery one less thing to worry about when given anesthesia. Earlier this month, two studies found that anesthesia can lead to cognitive dysfunction. In one study, researchers injected mice at different stages of their lives with an anesthetic called isoflurane. They found that it was toxic to a cell that helps control memory and learning, called the dentate gyrus. The researchers believe these effects could also occur in humans.

"We found something very interesting, in that cell death occurred in the spot where the dentate gyrus forms new neurons," Andreas Loepke, the study's lead author and researcher in the department of anesthesiology at Cincinnati Children's Hospital Medical Center, told Fox News.

Doctors already tell patients that they may experience changes in their mental capacity after surgery.

"The real answer is we don't know what the long term effects are," Dr. Jeffrey Silverstein, a professor of anesthesiology, surgery, geriatrics, and palliative medicine at the Icahn School of Medicine at Mount Sinai Hospital in New York City, told Everyday Health. "We know that it takes a while, at least a couple of days, before you're really normal after you've had surgery. Older people take a longer time to return to normal, sometimes up to six months. Whether that's associated with anesthesia or the surgery or both is an open question."

The second study examined the effects of anesthesia on the elderly. It found that the initial decline in cognitive function after surgery, known as post-operative cognitive dysfunction (POCD), was associated with neuroinflammatory reactions in the brain, causing cells to degenerate.

The researchers concluded that preoperative evaluations should be taken before surgery for not only the elderly, but for people of all ages.


Nagele P, Brown F, Francis A, et al. Influence of Nitrous Oxide Anesthesia, B-Vitamins, and MTHFR Gene Polymorphisms on Perioperative Cardiac Events: The Vitamins in Nitrous Oxide (VINO) Randomized Trial. Anesthesiology. 2013.

Loepke A, Rylon H, Deng M, et al. Cell age-specific vulnerability of neurons to anesthetic toxicity. Annals of Neurology. June 2013.

Sztark F, Le Goff ML, Andre D, et al. Exposure to general anesthesia could increase the risk of dementia in the elderly. European Society of Anesthesiology. 2013.