Evaluation of rebreathing in various modifications of the Mapleson-D system.

Several modifications of the Bain system for nitrous oxide analgesia or general anesthesia were tested for rebreathing and retention of CO2. The classic Bain circuit causes the most rebreathing as measured by the fractional concentration of CO2 in a sample of inspired gas (FICO2), but stimulation of the respiratory system seems to allow near normal end tidal CO2 and arterial CO2 tensions. The most predictable systems that have the least amount of rebreathing are those that have the least dead space.