Anesthetic drugs can be divided into three groups—general anes-thetics, local anesthetics, and topical anesthetics.
General anesthetic drugs are further subdivided into two main types: those given by inhalation and those given intravenously.
Commonly used general anesthetics given by inhalation include:
· nitrous oxide
The absorption and elimination rates of an anesthetic are gov-erned by its solubility in blood. Inhalation anesthetics enter the blood from the lungs and are distributed to other tissues. Distribu-tion is most rapid to organs with high blood flow, such as the brain, liver, kidneys, and heart. Inhalation anesthetics are elimi-nated primarily by the lungs; enflurane, halothane, and sevoflu-rane are also eliminated by the liver. Metabolites are excreted in the urine.
Inhalation anesthetics work primarily by depressing the CNS, pro-ducing loss of consciousness, loss of responsiveness to sensory stimulation (including pain), and muscle relaxation. They also af-fect other organ systems.
Inhalation anesthetics are used for surgery because they offer more precise and rapid control of depth of anesthesia than injec-tion anesthetics do. These anesthetics, which are liquids at room temperature, require a vaporizer and special delivery system for safe use.
Of the inhalation anesthetics available, desflurane, isoflurane, and nitrous oxide are the most commonly used.
Inhalation anesthetics are contraindicated in the patient with known hypersensitivity to the drug, a liver disorder, or malignant hyperthermia (a potentially fatal complication of anesthesia char-acterized by skeletal muscle rigidity and high fever). (See Unusu-al but serious reaction andAdverse reactions to inhalation anes-thetics)
The most important drug interactions involving inhalation anes-thetics occur with other CNS, cardiac, or respiratory-depressant drugs. Inhalation anesthetics can cause CNS depression, cardiac arrhythmias, or depressed respirations, resulting in compromised patient status.