What is Local Anesthesia?*While the author is a physician anesthesiologist, nothing in this article is intended to represent medical advice. This hub is for informational purposes, only.
Lidocaine is an example of a local anesthetic. Local anesthetics can be injected into tissue or around nerves to cause numbing. The numbing will affect the area immediately surrounding the injection site when lidocaine is used for “local anesthesia”. Regional anesthesia makes use of the class of drugs called local anesthetics (like lidocaine) to numb a larger area of the body by numbing a nerve or group of nerves that supply that area.
To review and keep the terminology straight…
Local anesthetics are drugs that cause numbing of tissue
Local anesthesia specifically refers to the numbing of an area of skin or tissue at or near the injection site of a local anesthetic
Regional anesthesia also utilizes the drugs that are called local anesthetics, but in a more indirect manner. The local anesthetic is injected around nerves supplying the body part to be numbed.
How do Local Anesthetics Work?
Local anesthetics are often discussed in terms of their properties. Their onset time and duration of action, as well as their safety profile, may determine which anesthetic would be useful in certain situations.
The two general classes of local anesthetics are the amides and esters based on their chemical structure. Lidocaine is an amide local anesthetic.
Lidocaine, and local anesthetics in general, work by penetrating tissue and blocking pain signals from being transmitted along nerve endings, preventing the pain signal from reaching the brain. The nerve endings have channels for the electrolyte sodium (Na channels) on them. When tissue is disturbed, the channels open and sodium enters the cell, changing the electrical charge. This electrical change becomes the pain sensation when interpreted by the brain.
The local anesthetics are sodium channel blockers. In other words, they prevent sodium from entering the nerve endings, thus, preventing pain. This is perceived as numbness.
When is Lidocaine Used?
Lidocaine can be used as a cream, injection or even as a mist for the nose, mouth and throat. Lidoderm is a patch containing lidocaine, available by prescription, that is applied to the skin for various painful conditions.
Lidocaine is most commonly used for injection into skin, muscle and mucous membranes for it’s local numbing. It is also used in regional anesthesia like spinals, epidurals and nerve blocks.
Its most common use is as a local anesthetic, but it has also been used for it’s action on heart cells to help stop or stabilize some abnormal heart rhythms.
Lidocaine Side EffectsRedness at or near injection site
Itching at or near injection site
Blistering at or near injection site
Numbness lasting longer or spreading further than desired
Side effects and complications are more likely if you have certain medical conditions or in combination with some medications. Always tell your doctor about your medical history and medications.
Side Effects of Lidocaine?
The expected effect of lidocaine is numbness of the target tissue. There are very few side effects of lidocaine used in this way.
Side effects are those effects that accompany a medicine’s use. They are expected in a certain percent of the population using the medication. They are often bothersome, but not harmful.
Complications, on the other hand, are possible, but not expected effects. Precautions are taken to prevent complications and they are often, but not always, avoidable.
Complications of Lidocaine Use
Complications can occur for a variety of reasons. Overdose of lidocaine, injection or leakage into the wrong space or allergic reaction can lead to complications.
Allergic Reactions
Allergic reactions are rare. The amide local anesthetics like lidocaine don’t have nearly the potential for, or actual incidence of, allergic reaction as local anesthetics of the ester class. It is possible, but unlikely to have a true allergic reaction to lidocaine. Sometimes, the preservative used may cause a reaction, however. Also, lidocaine may be mixed with epinephrine (adrenalin) to prolong it’s duration of action. The epinephrine will increase heart rate and blood pressure, and can cause nausea and a hot flushing and feelings of anxiety. This is not an allergic reaction as many patients assume or have been told. It is an exaggerated effect of the normal response to epinephrine.
Injection or leakage into blood vessels and the circulation of lidocaine meant for other tissue can lead to overdose and signs of toxicity. This can also occur when too much lidocaine is injected anywhere in the body. The maximum safe dose of lidocaine is calculated based on body weight and perhaps age and coexisting medical conditions. It is metabolized by the liver and eliminated from the body in the urine, so if you have liver or kidney problems, be sure to tell your doctor before receiving an injection with lidocaine.
Unintended Injection
When lidocaine enters a space for which it is not meant, it can cause unwanted side effects and complications. For example, epidural medication administration requires many times the dose of medicine injected directly into the spinal fluid. If lidocaine meant for the epidural space enters the spinal fluid instead, the result is an unwanted spinal block with much more medicine than would normally be used for that purpose. In this situation, the spinal can spread and cause a “total spinal” which temporarily paralyzes breathing and affect the heart rate, conduction and blood pressure in dangerous ways. The same thing can happen with certain peripheral nerve blocks, especially an interscalene block given in the neck before shoulder surgery, since the epidural and spinal spaces are close to the injection site. For this reason, these blocks are (or should) only given by highly-trained professionals who are also certified in advanced life-saving techniques.
Lidocaine toxicity from absorption into the bloodstream is another potential complication.
What are the Signs of Lidocaine Toxicity?
Overdosage of lidocaine, or lidocaine absorbed into the circulation can cause toxicity with lidocaine, a serious and potentially fatal complication. The severity of the complication depends on the amount that reaches the circulation.
Signs of lidocaine toxicity include
Numb tongue or lips
Ringing in the ears
Bad taste in the mouth
Nausea
Sedation
More severe toxicity is manifested as seizures, respiratory and cardiac arrest and coma.
Treatment of toxicity includes supportive care – medications to stop seizures and to support the cardiovascular system are used. In addition, a lipid rescue solution is now becoming a front-line treatment to neutralize local anesthetic toxicity and minimize the complications from it.
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