Methane accumulation during closed-circuit anesthesia.

When using the closed-circuit PhysioFlex apparatus for ventilating patients with an O2/air mixture during total intravenous anesthesia (TIVA) for gynecologic laparoscopy, we noticed that the built-in infrared analyzer indicated unexpected values for halothane. In 10 ASA grade I or II patients, the breathing gases were analyzed at the end of the ventilation for the presence of methane, which could be traced in all patients. Mean concentration was 861 ppm after a mean closed-circuit anesthesia time lasting 78 min. The unexpected halothane concentration at the time of gas sampling indicated an average of 1.0%. The anesthetic vapor analysis by infrared absorption is clearly disturbed by the presence of methane.