N2O volumes absorbed and excreted during N2O anesthesia in children.

Exhaled volumes were measured in 8 children during uptake and elimination of 3 percent and 75 percent N2O, using a volume-controlled ventilator. Absorption of 75 percent N2O during induction reduced the exhaled minute volume, which fell a mean of 16 percent in the 1st or 2nd minute and returned to normal by 15 to 20 minutes. Elimination was the mirror image of uptake; the mean increase in the exhaled minute volume was 13 percent. The concentration effect during uptake was measured (3 percent versus 75 percent N2O) and the data were used to calculate a fall in alveolar volume of at least 8 percent by the 2nd minute of uptake. The type of ventilation (volume-limited, pressure-limited, or spontaneous) was seen to have a modifying role on the respiratory pattern caused by the absorbed and excreted volume of N2O.