It takes careful training to know exactly how much anesthetic to administer, as well as which ones to use. Larger people may need more, while people with certain health conditions might not tolerate certain drugs as well as others. Some people just have higher or lower tolerances. It seems hard to imagine that something as benign as hair color would be related to anesthesia, but recent studies indicate that redheads may not only be more sensitive to pain, but also have a higher tolerance for both local and general anesthetics. To learn more, read Do redheads need extra anesthesia?
Local Anesthesia: No Longer Cocaine!
If you've had procedural sedation and think you know everything there is to know about anesthesia, think again -- local anesthesia is very different. Patients still remain awake and conscious but don't get the dreamy or sleepy state that accompanies procedural sedation.
This is another form of anesthesia that you've likely experienced before. For example, in addition to procedural sedation during dental work, dentists also use a local anesthetic when they inject your gum to numb the area. Local anesthesia is used to make a very small area of the body, such as a patch of skin, insensitive to pain. It typically provides both analgesia and paralysis by blocking the nerves' impulses so they can't travel to the brain, but patients may still feel pressure and sensation.
Local anesthetics can be topical, or isolated just to the surface. These are usually in the form of gels, creams or sprays. They may be applied to the skin before the injection of a local anesthetic that works to numb the area more deeply, in order to avoid the pain of the needle or the drug itself (penicillin, for example, causes pain upon injection). Topical anesthetics aren't just used in medical procedures -- if you've ever used a pain relief product for a rash or hemorrhoids, you've used a topical anesthetic. The type of local anesthetic you inject might be given before procedures like stitches or debridement (the removal of dead or damaged tissue).
Drugs used in local anesthesia usually end in the suffix "-aine" (such as lidocaine, novocaine or tetracaine) because they're chemically very similar to cocaine -- the first local anesthetic. The problem with using cocaine as an anesthetic is that it's addictive and highly stimulating to the cardiovascular system, so synthetic alternatives were developed. Some of these drugs have negative side effects of their own, such as allergic reactions, and have fallen out of favor. This is why dentists today typically use lidocaine instead of novocaine. The other issue with these drugs is that they're vasodilators, which means that they widen blood vessels and could lead to excessive bleeding, but epinephrine can counteract this effect.
Local anesthesia usually wears off within four to five hours. The pain relief lasts longer than the actual procedure most of the time. There are usually very few side effects, but patients do have to be careful with the numbed area -- if you leave the dentist's office unable to feel half your face, you might accidentally bite your cheeks. In rare cases, injected local anesthetics can cause nerve damage, but they're typically low-risk if administered correctly to a healthy person.
In the next section, we'll look at a related type of anesthesia: regional.