Local anesthetic

A local anesthetic is a medication used to cause an absence of all sensation in a specific body part. This includes the loss of pain, but unlike general anesthesia, it does not cause a loss of consciousness. While general anesthesia eliminates sensation throughout the entire body, local anesthesia is targeted. When these drugs are applied to specific nerve pathways, a process called a local anesthetic nerve block, they can also induce paralysis. This means the patient loses muscle function in that area as well.

Scientists classify these medications into two main chemical groups. These are known as amino esters and amino amides. Many modern versions are synthetic, meaning they are made in a lab. These synthetic versions are different from cocaine, which was used as an anesthetic in the past. Synthetic drugs have a much lower potential for abuse. They also generally do not cause hypertension or vasoconstriction, which is the narrowing of blood vessels. Interestingly, many of these drug names end with the suffix "-caine." This naming convention is derived from the word cocaine.

Doctors choose specific drugs based on their potency and how long they last. Some medications have a short duration of action and low potency, such as benzocaine, procaine, or chloroprocaine. Others offer a medium duration and medium potency, including articaine, lidocaine, and prilocaine. For procedures requiring more intense relief, high-duration and high-potency drugs are used. These include tetracaine, bupivacaine, cinchocaine, and ropivacaine.

There are several techniques for administering these drugs. Topical anesthesia involves applying a cream, gel, ointment, or spray to a surface. To help the medicine soak in deeper, it may be dissolved in solvents like DMSO. Other methods include infiltration, where the drug is injected into tissue. More complex methods involve blocks, such as a brachial plexus block, an epidural block, or spinal anesthesia. Spinal anesthesia is also known as a subarachnoid block. Other uses include iontophoresis and even using drugs like lidocaine as anti-arrhythmic agents to help with heart rhythms.

Local anesthetics are vital in many medical fields. In dentistry, they are used for fillings, crowns, root canals, and extractions. Podiatrists use them for surgeries on the feet, such as bunionectomies or hammertoe repairs. They are also essential in eye surgery, such as during cataract removal. Surgeons performing heart, lung, or abdominal operations often use epidural or spinal anesthesia. Even during diagnostic tests like a lumbar puncture or bone marrow aspiration, these drugs make the process less painful. They are also used to help place medical devices like pacemakers or chemotherapy ports.

While generally safe, local anesthesia can cause side effects. At the injection site, tissue swelling or edema may occur. The area might also look white, which is called blanching. This happens because vasoconstriction prevents blood flow to the area. This effect usually wears off in less than two hours. There is also a risk of a haematoma, which is a collection of blood caused by accidental damage to a blood vessel. While permanent nerve damage is rare, it can happen. Most people, about 92 to 97 percent, recover from nerve injury within four to six weeks.

Systemic effects can occur if the drug reaches high levels in the bloodstream. This might happen if a dose intended for an epidural is accidentally injected into a vessel. High concentrations can affect the central nervous system, causing symptoms like ringing in the ears, dizziness, or even seizures. In very severe cases, it can lead to coma or respiratory arrest. Additionally, a patient's emotional state can cause a vasovagal collapse. This is a reaction to fear or nervousness that can cause paleness, sweating, or a temporary loss of consciousness. Medical professionals work to keep patients comfortable to avoid these reactions.