A local anesthetic (LA) is a medication that causes absence of all sensation (including pain) in a specific body part without loss of consciousness, as opposed to a general anesthetic, which eliminates all sensation in the entire body and causes unconsciousness. Local anesthetics are most commonly used to eliminate pain during or after surgery. When it is used on specific nerve pathways (local anesthetic nerve block), paralysis (loss of muscle function) also can be induced.
Classification
LAs are of 2 types: Clinical LAs: amino amide LAs amino ester LAs Synthetic LAs Cocaine derivatives
Synthetic cocaine-derived LAs differ from cocaine because they have a much lower abuse potential and do not cause hypertension vasoconstriction (with few exceptions).
The suffix "-caine" at the ends of these medication names is derived from the word "cocaine", because cocaine was formerly used as a local anesthetic.
Examples
Short Duration of Action and Low Potency
Benzocaine
Procaine
Chloroprocaine
Medium Duration of Action and Medium Potency
Lidocaine
Prilocaine
High Duration and High Potency
Tetracaine
Bupivacaine
Cinchocaine
Ropivacaine
Medical uses
Local anesthetics may be used to prevent and/or treat acute pain, to treat chronic pain, and as a supplement to general anesthesia.
They are used in various techniques of local anesthesia such as: Topical anesthesia (surface anesthesia) Topical administration of cream, gel, ointment, liquid, or spray of anesthetic dissolved in DMSO or other solvents/carriers for deeper absorption Infiltration Brachial plexus block Epidural block (extradural) Spinal anesthesia (subarachnoid block) Iontophoresis Diagnostic purposes (e.g. dibucaine) Anti-arrhythmic agents (e.g. lidocaine).
Acute pain
Even though acute pain can be managed using analgesics, conduction anesthesia may be preferable because of superior pain control and fewer side effects. For purposes of pain therapy, LA drugs are often given by repeated injection or continuous infusion through a catheter. LA drugs are also often combined with other agents such as opioids for synergistic analgesic action. Low doses of LA drugs can be sufficient so that muscle weakness does not occur and patients may be mobilized.
Some typical uses of conduction anesthesia for acute pain are:
Chronic pain
Chronic pain is a complex and often serious condition that requires diagnosis and treatment by an expert in pain medicine. LAs can be applied repeatedly or continuously for prolonged periods to relieve chronic pain, usually in combination with medication such as opioids, NSAIDs, and anticonvulsants. Though it can be easily performed, repeated local anesthetic blocks in chronic pain conditions are not recommended as there is no evidence of long-term benefits.
Surgery
Virtually every part of the body can be anesthetized using conduction anesthesia. However, only a limited number of techniques are in common clinical use. Sometimes, conduction anesthesia is combined with general anesthesia or sedation for the patient's comfort and ease of surgery. However, many anesthetists, surgeons, patients and nurses believe that it is safer to perform major surgeries under local anesthesia than general anesthesia. Typical operations performed under conduction anesthesia include:
Diagnostic tests
Diagnostic tests such as bone marrow aspiration, lumbar puncture (spinal tap) and aspiration of cysts or other structures are made to be less painful upon administration of local anesthetic before insertion of larger needles.
Other uses
Local anesthesia is also used during insertion of IV devices, such as pacemakers and implantable defibrillators, ports used for giving chemotherapy medications and hemodialysis access catheters.
Topical anesthesia, in the form of lidocaine/prilocaine (EMLA) is most commonly used to enable relatively painless venipuncture (blood collection) and placement of intravenous cannulae. It may also be suitable for other kinds of punctures such as ascites drainage and amniocentesis.
Surface anesthesia also facilitates some endoscopic procedures such as bronchoscopy (visualization of the lower airways) or cystoscopy (visualization of the inner surface of the bladder)