The use of nitrous oxide for general anesthesia may increase patients' long-term risk of heart attack, a new study shows, although more research is needed to assess the true cardiovascular risks associated with the anesthetic gas.

In a follow-up study to a previous randomized trial of 2,050 patients undergoing non-cardiac surgery under general anesthesia with or without nitrous oxide, researchers from Royal Melbourne Hospital found nitrous oxide to be associated with a greater long-term risk of myocardial infarction.

The original study showed higher rates of heart attack and death among the nitrous oxide group in the short term (within 30 days of surgery), while the follow-up did not indicate that the long-term risk of stroke or death was higher for nitrous oxide patients. However, the risk of myocardial infarction was nearly 60% greater among the nitrous oxide group at a median follow-up of 3 and a half years after surgery.

Although the results point to a risk of cardiac complications associated with the anesthetic, the authors say their study is not definitive and that more research is needed. "The exact relationship between nitrous oxide administration and serious long-term adverse outcomes requires investigation in an appropriately designed large randomized controlled trial," concludes the study, published in the journal Anesthesia & Analgesia.

Irene Tsikitas

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