Anesthesia is an absence of sensation, which may be of three types: general, local, or pathological. General anesthesia is a reversible state of drug-induced suppression of reflexes, which facilitates many surgical procedures and avoids distress. An anesthesiologist attends to ensure stable anesthesia and to protect vital functions. While ethanol and narcotics have been used for their anesthetic properties for centuries, modern anesthesia dates from the use of diethyl ether by William Morton in 1846, and of chloroform by James Simpson in 1847 (see history of surgery).
Nowadays injection of short-acting barbiturates, such as sodium penthothal, is frequently used to induce anesthesia rapidly; inhaled agents, including halothane, ether, nitrous oxide, trichloroethylene, and cyclopropane, are used for induction and maintenance. Local and regional anesthesia are the reversible blocking of pain impulses by chemical action of cocaine derivatives (e.g., procaine, lignocaine). Nerve trunks are blocked for minor surgery and dentistry, and more widespread anesthesia may be achieved by blocking spinal nerve roots, useful in obstetrics and patients unfit for general anesthesia. Pathological anesthesia describes loss of sensation following trauma or disease.
Epidural anesthesia involves the injection of a local anesthetic into the epidural space surrounding the spinal cord. It is done to anesthetize the spinal nerve roots and so prevent pain during surgery or childbirth.