The use of inhalational anesthetics is generally reserved for maintenance of anesthesia. The development of an anesthetic concentration in the brain occurs more slowly with inhalational anesthetics than with IV drugs. Once an anesthetic level has been achieved, however, it is easily adjusted by controlling the rate or concentra-tion of gas delivery from the anesthesia machine. The rate of recovery from a lengthy procedure in which in-halational agents are used is reasonably rapid, since in-halational anesthetics are eliminated by the lungs and do not depend on a slow rate of metabolism for their tissue clearance. Thus, inhalational drugs meet the re-quirement for a relatively prompt return of the patient’s psychomotor competence.
Pharmacokinetic factors that influence the distribu-tion of gases control the establishment of anesthetic concentrations in tissue. Thus, factors influencing gas distribution in tissues are important to the anesthesiol-ogist, who must control anesthetic delivery and adjust for physiological influences and/or pathological condi-tions that can alter the accumulation of the gas. Unlike most drugs whose equilibration with tissues involves concentration gradients, partial pressure gradients con-trol the equilibration of gases between various tissue compartments.