Nitrous oxide pneumoperitoneum revisited

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Abstract
Nitrous oxide has been effectively banned from use in therapeutic laparoscopy because of fear of combustion. These fears rest on two case reports, a misunderstanding of the physical chemistry of nitrous oxide, and lack of information on the presence of flammable colonic gases in the pneumoperitoneum mixture. This study aims to identify the presence and quantify the amount of hydrogen and methane found in the peritoneal cavity during laparoscopic GI procedures, and then to compare the gas concentrations detected with known limits of combustion. Gas standards with known concentrations of hydrogen and methane were placed in polypropylene syringes and analyzed on a mass spectrometer after 1, 2, 3, and 4 h. This established the rate at which these gases would be leached through a polypropylene syringe—the amount of gas lost during transport from the patient to the laboratory. Twenty gas samples were drawn, randomly, 30 min to 2 h following the start of laparoscopic gastrointestinal procedures. The samples were analyzed for hydrogen and methane within 30 min of their aspiration from the abdominal cavity. An inconsequential amount of methane was lost from the polypropylene syringe in 4 h. After 1 h, one-half the hydrogen had leached from the polypropylene syringe. Hydrogen was detected in the pneumoperitoneum of four patients at a concentration ranging from 0.016 to 0.075%. No methane was detected in any sample. For combustion to occur in a nitrous oxide environment, hydrogen or methane must occupy 5.5% of the gas volume. The maximum amount of hydrogen we detected was less than 1/50 of the combustion threshold. After considering these data, and a large clinical experience of gynecologic laparoscopy using electrosurgery in a nitrous oxide pneumoperitoneum, we conclude that nitrous oxide can be safely used for creating a pneumoperitoneum during laparoscopic surgery.