Nitrous Oxide as a Marker for Irrigating Fluid Absorption

Abstract

Objective: To study whether tracer amounts of a gas, nitrous oxide (N[Formula: See Text]O), might be a suitable marker for absorption of irrigating fluid during endoscopic procedures. Material and Methods: N[Formula: See Text]O was dissolved to a concentration of 10% in a commercially available irrigating fluid containing 3% mannitol and 1% ethanol. Seven experiments involving administration of the fluid via either the i.v. or i.p. route were performed in three pigs under general anesthesia. The N[Formula: See Text]O concentration and, in one pig, the ethanol concentration, were measured in the expired breath. Results: The N[Formula: See Text]O method readily detected i.v. bolus injections of 2, 10 and 20 ml quantities of irrigating fluid. Continuous administration of the fluid over a 20-min period showed that the N[Formula: See Text]O concentration increased and decreased very rapidly when the infusions were turned on and off, while a quasi-steady state was reached after ≈2 min. The maximum breath N[Formula: See Text]O concentration during a 600-ml infusion was 0.05%. The breath ethanol concentration rose as fast as the N[Formula: See Text]O level but decreased more slowly when the infusion was turned off. As with ethanol, the N[Formula: See Text]O responses were much slower when the fluid was given by i.p. infusion, and the maximum concentration was only one-third of that during i.v. infusion. Conclusions: Dissolving N[Formula: See Text]O in irrigating fluid offers the possibility of detecting an administered fluid volume in the exhaled breath in the same way as for ethanol. The advantages of N[Formula: See Text]O include better resolution, lower toxicity and rapid elimination.

• Irrigation
• Mannitol
• Nitrous Oxide
• Complications