This article focuses on the neurologic complications of drugs used for local anesthesia as well as the procedures involved. The most common adverse reactions to local anesthetic agents are seizures. Neurologic deficits, both sensory and motor, usually correspond to the blocked nerves. These may be transient or permanent. Adjuvant agents used for enhancing the effect of local anesthetics may also have neurotoxic effects. Suggestions are made for reducing the neurologic complications of local anesthesia.
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• Local anesthetics may cause adverse effects either by action on the nerves and muscles or neurotoxicity following systemic absorption.
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• Injection injury of neural structures may result from the procedure.
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• Seizures are a frequent adverse effect of local anesthetics, and principles of management are those applicable to drug-induced seizures.
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• Careful selection of the anesthetic agent and meticulous procedure for local anesthesia are important preventive measures.
Historical note and terminology
Local anesthetics are substances that produce a reversible loss of sensation or analgesia when applied to body tissues. This is achieved by interference with nerve conduction in the peripheral nerves.
Induction of analgesia by application of substances directly to the wound goes back to the dawn of medical history. About 1000 years ago, Arab physicians used opium as a local anesthetic in patients with dental pain, earache, or joint pain (02). Cocaine, isolated from the leaves of Erythroxylum coca in 1860, was the first modern local anesthetic. Its local anesthetic properties on the skin were described in 1880, and its usefulness as a topical anesthetic for the eye was demonstrated in 1884 (17). Various adverse effects of local anesthesia, such as syncope and seizures have been reported since the 1960s. Neurologic complications of cocaine have been well documented (14). Because of the abuse potential and neurotoxicity, cocaine use has declined as a local anesthetic. It is sometimes used in endonasal surgery because it is the only substance that has combined local anesthetic and vasoconstrictor effects. Safer local anesthetics are available as alternatives and can be combined with 1:1000 epinephrine for vasoconstrictor effect.
Use of local anesthetics is limited by their duration of action and the dose dependent adverse effects on the cardiac and central nervous systems. This article will primarily describe the neurologic adverse effects of local anesthetics; complications of anesthesia administration and other technical errors will also be mentioned. Regional anesthesia with the use of local anesthetics will be included in this discussion, except epidural anesthesia, which is the subject of a separate article. Local anesthetics include the following: lidocaine, ropivacaine, bupivacaine, mepivacaine, tetracaine, prilocaine, procaine, procainamide, and benzocaine. Complications may occur due to use of adjuvant agents for potentiating the effect of local anesthetics by synergism or to prolong the duration of anesthesia and limit the cumulative dose required (30). Drugs used to potentiate the effect of local anesthetics include opioids, epinephrine, alpha-2 adrenergic antagonists, steroids, antiinflammatory drugs, midazolam, ketamine, remifentanil, and dexmedetomidine.
Local anesthesia is used widely in most branches of medicine and is generally considered to be safer than general anesthesia. However, serious neurologic complications can occur.