Treatment that dulls or blocks normal sensation, including pain, and that is usually given before a surgical procedure. There are three basic types of anesthesia: general, regional, and local.

People under general anesthesia are unconscious, feel no pain, and have no memory of their time under anesthesia. For these reasons, general anesthesia is commonly used for longer and more complex surgeries, such as those involving organs in the chest or upper abdomen. The anesthesia is usually brought on by intravenous drugs and inhaled gases.

During a procedure that uses general anesthesia, a tube is typically inserted into a person’s throat to provide oxygen. During the surgery, anesthesiologists — doctors who specialize in administering anesthesia — carefully monitor people with electronic devices that continually display vital signs, including blood pressure, blood oxygen levels, heart function, temperature, and breathing patterns. Although general anesthesia can cause heart attacks, stroke, and infections, these and other serious side effects are rare in healthy people. People who have heart problems, who take drugs that increase bleeding, who smoke or drink, and who are obese are at higher risk of complications from general anesthesia.

Regional anesthesia numbs one area of the body, such as a limb, without making a person unconscious. In regional anesthesia, drugs are administered either to the spine or to nerves elsewhere in the body. When administered to the spine, the two most common procedures are spinal blocks and epidural blocks. In a spinal block, pain-relieving drugs are injected into the fluid around the spine in the lower back. The drugs block pain signals from the lower body, numbing the entire area below the waist. An epidural block is similar to a spinal block, except that it uses a catheter to transmit the pain-relieving drugs to the spine. Also, whereas a spinal block is always performed on the lower back and numbs only the lower body, an epidural can be inserted into the middle or upper spine to numb parts of the upper body. One advantage of an epidural block is that the catheter can be left in to provide pain relief after the surgery. Epidural blocks are well known from their use in women during childbirth.

Another type of regional anesthesia, often called a nerve block, uses injections of pain-relieving drugs into nerves not in the spine to numb a particular part of the body. For example, a nerve block in the arm may be used during hand surgery. A nerve block in the groin may be used for surgery in the thigh or knee.

Local anesthesia is used to numb a smaller area of the body. Examples of local anesthesia are gum injections given for dental procedures and topical drugs that numb the skin before an injection.

For some surgeries, there may be a choice of either general or regional anesthesia. For example, Cesarean sections, breast biopsies, cataract surgery, hernia repair, and some types of plastic surgery may use either type of anesthesia. For people with arthritis, a total hip or knee replacement can be performed with either type of anesthesia as well. In many cases, regional anesthesia — whether spinal block, epidural block, or nonspinal nerve block — is preferred because of a lower risk of side effects, less postoperative pain, and a quicker recovery.

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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