Nitrous oxide and carbon dioxide have no effect on the blood-gas solubilities of sevoflurane and isoflurane

Nitrous oxide (N2O) has been shown to decrease the solubility (lambda(B:G)) of volatile anesthetics in human blood and, consequently, affect their rate of uptake. If this is true, then carbon dioxide (CO2) may also have an effect, which is important because methods that measure the tension of volatile anesthetics in blood washout CO, in the process. Blood samples were obtained from fasted, healthy volunteers and patients undergoing major surgery. Each sam pie was divided into two aliquots: one was equilibrated at 37 degrees C in a closed glass tonometer with a mixture of isoflurane 1% and sevoflurane 2% in a test gas mixture of either 50:50 N2O/O-2 or 5:95 CO2/O-2; the other aliquot was equilibrated with isoflurane and sevoflurane in O-2 alone as a control. Using a two-stage headspace technique using gas chromatography, we measured the lambda(B:G) of isoflurane and sevoflurane in the presence and absence of the test gas in each subject. There was no significant difference between the lambda(B:G) of sevoflurane and isoflurane obtained from the N2O group and their controls or between the CO2 group and their controls. We conclude that neither N2O nor CO2 has an effect on the lambda(B:G) of sevoflurane or isoflurane in the concentrations tested. Implications: The blood solubilities of sevoflurane and isoflurane were measured with and without nitrous oxide and carbon dioxide. No differences were found. Nitrous oxide does not affect the kinetics of other anesthetics by altering their solubility. Carbon dioxide tensions need not be controlled when measuring anesthetic tensions in blood.