The effect of nitrous oxide on laryngeal mask cuff pressure.

During general anesthesia with the laryngeal mask airway (LMA), a significant increase in cuff pressure due to diffusion of nitrous oxide through the cuff wall occurs. This descriptive clinical study was conducted in a university teaching hospital ambulatory surgical center with 100 patients (ASA physical status, I-III; age, 5 months to 76 years; weight, 5.8-146.3 kg) undergoing general anesthesia with an LMA. The airway pressure at which the LMA seal was broken (leak pressure) was determined immediately after the insertion of the LMA. The LMA leak pressure was determined by closing the circuit pop-off valve and recording with a stethoscope at the neck the pressure at which the gas was first heard to escape around the LMA. The LMA cuff pressure was determined by connecting the check valve of the LMA pilot balloon to a sphygmomanometer. The mean LMA cuff pressure increased 16 +/- 8.2 mm Hg (1- to 30-minute group), 38.11 +/- 15.87 mm Hg (31- to 60-minute group), 39.53 +/- 16.9 mm Hg (61- to 90-minute group), 42.63 +/- 20.36 mm Hg (91- to 120-minute group), and 44.25 +/- 14.03 mm Hg (120- to 350-minute group). This study demonstrated that there was a gradual increase in the cuff pressure well over a 3-hour period during nitrous oxide and oxygen anesthesia.