How Anesthesia Works

Sometimes, the terms "local anesthesia" and "regional anesthesia" are used interchangeably. For the purposes of this article, we'll use regional anesthesia to describe anesthesia that's used in a wider region of the body. For example, while local anesthesia may be used to numb an area on the leg, regional anesthesia can numb the entire leg. This is known as peripheral regional anesthesia because it blocks a single nerve or specific bundle of nerves. The other type of regional anesthesia is central anesthesia, which usually involves an injection into the cerebrospinal fluid or the epidural space just outside the spinal canal.

Regional anesthesia is also known as a nerve block. Some of the same drugs that we learned about in the local anesthesia section are used in regional anesthesia -- they're just used in larger dosages and have a stronger effect on the central nervous system. Patients can remain conscious for procedures under regional anesthesia, but they may also be sedated during the administration of the block, during the medical procedure or during both. This depends on the procedure as well as the patient's preference -- some people would rather not be conscious.

Sometimes regional anesthetics are given with a single injection, but they can also be given intravenously or continuously through a catheter. One technique, called a Bier block, uses a tourniquet to keep blood from flowing through a limb before the drug is injected into a vein. (It can only be used with a relatively short procedure, though.)

Women who have given birth are probably very familiar with the central anesthetic technique known as an epidural. In this procedure, an anesthesiologist inserts a catheter into the epidural space, typically in the lower back area. This continuously feeds drugs such as lidocaine as well as fentanyl or clonidine to provide pain relief, resulting in a loss of sensation from the waist down.

Spinal blocks, which are injected into the cerebrospinal fluid, are often used for other procedures below the waist, such as Cesarean sections or hernia surgery. They tend to paralyze further than epidurals. While patients are usually awake for a spinal block during a C-section, they may be sedated for other procedures.

Regional anesthesia carries more risks than local anesthesia, such as seizures and heart attacks, because of the increased involvement of the central nervous system. Sometimes regional anesthesia fails to provide enough pain relief or paralysis, and switching to general anesthesia is necessary.

Patients under regional anesthesia need strict monitoring, which we'll look at in the next section.