Uptake and clearance of inhalation anesthetics in man

The uptake, distribution, and clearance of inhaled vapors is governed by rules of partial pressure equilibration in a multicompartmental system. Since halogenated anesthetic agents are not soluble in water, biotransformation is their only clearance pathway during anesthesia. When apparent steady state is reached, the rate of overall metabolism can be determined from the pulmonary uptake rate. As a result of metabolism, pulmonary uptake increases but the concentration of inhaled vapor in blood and tissues decreases, and only a fraction of uptake is exhaled following anesthesia. Uptake and pulmonary clearance of five halogenated anesthetic agents were studied in 45 surgical patients. The susceptibility to biotransformation increases in the following order: isoflurane, enflurane, halothane, fluroxene, methoxyflurane.