Nitrous oxide decreases solubility of isoflurane and halothane in blood

This study investigated the effects of carrier gases on the solubility of isoflurane or halothane in blood. The blood/gas partition coefficients (lambda blood/gas) of 1 minimum alveolar anesthetic concentration of isoflurane or halothane in 100% oxygen, 30% oxygen with 70% nitrous oxide, 100% nitrous oxide or air were measured at 37 degrees C, with blood from four donors. The values of isoflurane or halothane in 100% nitrous oxide (1.42 +/- 0.03; 2.59 +/- 0.05) were lower (P < 0.05) than those obtained when using 100% oxygen (1.53 +/- 0.02; 2.71 +/- 0.05) or air (1.54 +/- 0.03; 2.74 +/- 0.05). To determine the effect of absence of oxygen in the blood containing nitrous oxide on solubility, lambda blood/gas of 1 minimum alveolar anesthetic concentration of isoflurane or halothane in 100% oxygen, a gas mixture (30% oxygen and 70% nitrous oxide) or 100% nitrous oxide were measured under the same conditions. The values of isoflurane or halothane in 100% nitrous oxide (1.29 +/- 0.03; 2.25 +/- 0.08) and in a gas mixture of 30% oxygen and 70% nitrous oxide (1.33 +/- 0.04; 2.29 +/- 0.05) were lower (P < 0.05) than those obtained with 100% oxygen (1.40 +/- 0.03; 2.37 +/- 0.04). We conclude that nitrous oxide decreases the lambda blood/gas of isoflurane or halothane, and that this change of solubility, although small, increases the uptake rate of halothane or isoflurane.