2. a drug or agent used to abolish the sensation of pain, to achieve adequate muscle relaxation during surgery, to calm fear and allay anxiety, and to produce amnesia for the event.
Inhalational anesthetics are gases or volatile liquids that produce general anesthesia when inhaled. The commonly used inhalational agents are
halothane,
enflurane,
isoflurane, and
nitrous oxide. Older agents, such as
ether and
cyclopropane, are now used infrequently. The mechanism of action of all inhalational anesthetics is thought to involve uptake of the gas in the lipid bilayer of cell membranes and interaction with the membrane proteins, resulting in inhibition of synaptic transmission of nerve impulses. For surgical anesthesia, these agents are usually used with preanesthetic medication, which includes
sedatives or
opiates to relieve preoperative and postoperative pain and
tranquilizers to reduce
anxiety. Neuromuscular blocking agents are used as
muscle relaxants during surgery. They include
tubocurarine,
metocurine,
succinylcholine,
pancuronium,
atracurium, and
vecuronium.
Intravenous anesthetics are sedative hypnotic drugs that produce anesthesia in large doses. The most common of these are the phenol derivative
propofol and ultra–short acting
barbiturates such as
thiopental and
methohexital; these can be used alone for brief surgical procedures or for rapid induction of anesthesia maintained by inhalational anesthetics.
Other intravenous methods of anesthesia are
neuroleptanalgesia, which uses a combination of the butyrophenone tranquilizer
droperidol and the opioid
fentanyl;
neuroleptanesthesia, which uses neuroleptanalgesia plus
nitrous oxide; and
dissociative anesthesia, which uses
ketamine, a drug related to the hallucinogens that produces profound analgesia.
Local anesthetics are drugs that block nerve conduction in the region where they are applied. They act by altering permeability of nerve cells to sodium ions and thus blocking conduction of nerve impulses. They may be applied topically or injected into the tissues. The first local anesthetic was
cocaine. Synthetic local anesthetics are all given names ending in
-caine; examples are
procaine and
lidocaine.