General anesthetics (inhalational and intravenous agents) have a rapid, smooth onset of action and clinically desirable rapid reversal of effect. Concentrations of inhalational agents in the body and the pharmacokinetics depend on the drugs’ partial pressure in the lungs and solubility in blood and brain tissue. Induction of anesthesia is more rapid for drugs with high partial pressure in the lungs and high solubility in blood (eg, nitrous oxide, desflurane, sevoflurane). Onset of anesthesia is slowed when pulmonary blood flow is reduced.
The site of drug action is
the brain; the exact mechanism is unknown but may be related to lipid solubility and
activation of GABAA receptors (enhanced Cl− influx,
hyperpolarization of neurons). Elimination from brain and exhalation from lungs
stop the effect of the drug. Redistribution to other tissues delays elimination
and may increase occurrence of adverse effects. Intravenous agents include
barbiturates, benzodiazepines, ketamine, opioids, and propofol.