Comparison of Uptake and Elimination of Volatile Anesthetics

Kim, Soon Im; Kim, Sun Jong; Kim, Sung Yell

Abstract

To compare the rate of uptake and elimination of volatile anesthetics, we administered 2% Halothane, 2% Enflurane and 2% Isoflurane respectively for one hour to 90 healthy adult patients through a semicolsed circuit with controlled ventilation to maintain normocapnea for determining the rates of uptake, and the volatile anesthetics and nitrous oxide were discontinued to determine the rates of elimination for 30 minutes. The expired(Fe=Fa) and inspired(F1) vapor concentrations of volatile anethetics were measured using an infrared analyser and F(A)/ F(1) ratios were used to determine rates of uptake, and F(A)/F(AO)(Where F(AO) is the last end-tidal concentration during uptake) ratios were used to determine rates of elimination. And to evaluate the effects of gas flow pattern on the rate of uptake and elimination, the patients were divided into three groups: Control group inhaled three volatile anesthetics respectively with 3 liter of oxygen per minute, study group 1 inhaled three volatile anesthetics respectively with 6 liter of oxygen per minute and study group 2 inhaled three volatile anesthet- ics respectively with 1 liter of oxygen and 2 liter of nitrous oxide. The results obtained were as follows: l) To compare the rate of uptake(F(A)/F(1)) of the anesthetics, the pulmonary uptake was most rapid with isoflurane followed by enflurane and halothane in accord with their respective solubilities in blood 2) With increased fresh gas flow, the rates of uptake of anesthetics more rapidly augmented, especially significantly in halothane and enflurane 3) With gas mixture of 70% N2O, the rate of uptake of anesthetics more rapidly augmented, especially significantly in isoflurane and enflurane 4) To compare the rate of elimination of anesthetics, isoflurane and enflurane eliminated more rapidly than halothane but there are no difference in that of isoflurane with enflurane in control group. But there are no difference significantly between that of halothane, enflurane and isoflurane in study group 1 and 2. 5) With increased gas flow rate, the rate of elimination decreased more rapidly in halothane, enflurane and isoflurane significantly. 6) By the elimination of anesthetics with N2O simultaneously from the lung, the rate of elimination decreased more rapidly in halothane and isoflurane significantly. In conclusion, we have shown that we can obtained more rapid induction and recovery of inhalation anesthetics with lower solubility of anesthetics. In addition, with increased fresh gas flow and use of gas mixture af nitrous oxide, induction and recovery of anesthetics will be more rapidly.