Pharmacokinetics of Desflurane, Sevoflurane, Isoflurane, and Halothane in Pigs

We tested the prediction that the alveolar washin and washout, tissue time constants, and pulmonary recovery (volume of agent recovered during washout relative to the volume taken up during washin) of desflurane, sevoflurane, isoflurane, and halothane would be defined primarily by their respective solubilities in blood, by their solubilities in tissues, and by their metabolism. We concurrently administered approximately one-third the MAC of each of these anesthetics to five young female swine and determined (separately) their solubilities in pig blood and tissues. The blood/gas partition coefficient of desflurane (0.35 +/- 0.02) was significantly smaller (P less than 0.01) than that of sevoflurane (0.45 +/- 0.02), isoflurane (0.94 +/- 0.05), and halothane (2.54 +/- 0.21). Tissue/blood partition coefficients of desflurane and halothane were smaller than those for the other two anesthetics (P less than 0.05) for all tissue groups. As predicted from their blood solubilities, the order of washin and washout was desflurane, sevoflurane, isoflurane, and halothane (most to least rapid). As predicted from tissue solubilities, the tissue time constants for desflurane were smaller than those for sevoflurane, isoflurane, and halothane. Recovery (normalized to that of isoflurane) of the volume of anesthetic taken up was significantly greater (P less than 0.05) for desflurane (93% +/- 7% [mean +/- SD]) than for halothane (77% +/- 6%), was not different from that of isoflurane (100%), but was less than that for sevoflurane (111% +/- 17%). The lower value for halothane is consistent with its known metabolism, but the lower (than sevoflurane) value for desflurane is at variance with other presently available data for their respective biodegradations.