Genotoxic properties of nitrous oxide revealed yet again
By Peter Sergo, medwireNews Reporter
11 April 2013
Anesthesiology 2013; Advance online publication

medwireNews: Nitrous oxide administered to adult patients undergoing major elective open colorectal surgery is associated with DNA damage in peripheral leukocytes, a study finds.

Furthermore, DNA damage stemming from nitrous oxide anesthesia could be a cause of postoperative infection, researchers report in Anesthesiology.

The research team conducted a double-blind, randomized controlled trial involving 91 adult patients who received 70% nitrous oxide (n=31), or nitrous oxide-free anesthesia with either 30% (n=30) or 80% (n=30) oxygen.

Venous blood samples were collected immediately before and 24 hours after surgery to assess the extent of DNA damage in circulating leukocytes using single-cell gel electrophoresis (or "comet" assay).

Nitrous oxide exposure was associated with a significant twofold increase in the percentage of DNA intensity in the tail, which did not occur in the 30% or 80% oxygen groups.

There was also a significant, positive correlation between the duration of nitrous oxide exposure and extent of DNA damage that became more apparent when exposure lasted longer than 2 hours.

Postoperative complications based on ASEPSIS criteria showed a significantly higher rate of surgical wound infection in the nitrous oxide group (32%) in comparison to the other groups (7.3% and 8.7% for the 30% and 80% oxygen groups, respectively).

Yet a nitrous oxide effect on wound infection did not emerge when diagnosis was based on the Centers for Disease Control and Prevention criteria; 19.4% (6 of 31) in the 70% nitrous oxide group was nonsignificantly higher than the 6.7% (2 of 30) observed in both the 30% and 80% oxygen groups.

Notably, when the DNA intensity in the tail doubled in percentage after nitrous oxide exposure, wound infection risk more than doubled. Oxygen exposure did not have any measurable DNA affect.

"It should be understood that this finding does not imply a causal relationship," write Yen Chen (The Chinese University of Hong Kong, China) and colleagues. "Although DNA damage is one of the hallmarks in apoptosis, its immunosuppressive effect remains unclear. Future study should explore the mechanisms of DNA damage to produce wound infection."

In an accompanying editorial, Kirk Hogan (University of Wisconsin, Madison, USA) warned about other specialties "introducing or resurrecting" nitrous oxide in emergency care, pediatric sedation, dentistry, and labor and delivery. "Investigating… genotoxicity after nitrous oxide use in these settings might be of particular interest," he concludes.

medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013

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