How does local anesthesia work?

In the form of sprays, gels, patches, injections … Local anesthesia is a type of intervention that can be done in several ways but in all, it is a question of numbing a small area to avoid feeling pain.

Local anesthetics are used both at home, to treat a sore throat or gum discomfort, and in consultation with healthcare professionals, such as a dentist or dermatologist.

The mechanism of action of the drugs used in these procedures has the peculiarity of affecting the nerves, something that we will see more deeply when we see how does local anesthesia work in a word.

    How does local anesthesia work?

    Local anesthesia consists of using medicines to temporarily numb a small part of the body. This type of anesthesia is applied before undergoing a minor medical procedure, such as a skin biopsy and also during the consultation of the dentist for the extraction of a tooth or the installation of a filling.

    Unlike general anesthesia, local anesthesia does not make the patient fall asleep, intervening in the nerves of the area where it was applied. To understand how it works, you must first review how the nervous system works in general.

    As we know, in the nervous system we find cells called neurons, which have a membrane with many channels that allow ions, electrically charged molecules, to pass through them. The ions involved in the transmission of nerve impulses are mainly three in number: sodium (Na +), potassium (K +) and chlorine (Cl-).

    When a stimulus hits a sensory cell, a nerve signal is produced. This signal can be felt in different ways, for example in the form of temperature, pressure or in relation to the current subject of pain.

    In order for a nerve impulse to be generated, it is necessary to reach the threshold of electrical activation of the neuron and, if reached, it will lead to a process called depolarization.

    When the neuron is at rest, its exterior is positive and its interior is negative. This changes when a sufficiently intense stimulus is received, which causes the membrane channels to open, the introduction of Na + into the nerve cell and the output of K +, in a ratio of 3 to 2. In this way, the interior of the neuron becomes more positive, allowing the action potential to be given and therefore the nerve impulse to be transmitted.

    Having understood this, what does it have to do with how local anesthesia works? The truth is, the mechanism of action of local anesthetics directly affects the ability of neurons in the affected area to emit a pulse. Local anesthesia blocks the Na + channels of the neuronal membrane, preventing this ion from entering the neuron and turning its interior into a positive.. Because the interior remains negative, depolarization cannot occur.

    Local anesthesia prevents depolarization of the neuron, which means that the area under the effects of this intervention cannot transmit enough signals and therefore no pain is noticed in the area.

      Properties of these drugs

      There is a wide variety of local anesthetics and therefore their properties vary, although they all have in common that they are slightly alkaline. Because of that, these drugs do not work very well in acidic environments such as inflammation or infection, that is why it is not used in these medical conditions.

      Chemically, local anesthetics are molecules made up of an aromatic lipophilic ring attached to a hydrophilic group by an intermediate bond which may be of the ester or amide type. It’s just the type of connection that can be found in the anesthetic that causes it to be given one name or another, as well as an influence on how the body metabolizes the substance.

      Amide-type anesthetics are metabolized in the liver, while ester-type anesthetics are metabolized by pseudocholinesterases in the blood. Ester anesthetics, when metabolized, yield paraaminobenzoic acid as a metabolite which can cause allergies in some people.

      Usually, you can tell if a local anesthetic belongs to the ester group or the amide group by looking at its name.. In the case of amides, there is another “i” in their name besides what forms the suffix -caine, such as lidocaine, mepivacaine, prilocaine or ropivacaine, while in esters there is no has that the “i” of -cain, as can be seen in chloroprocaine, procaine, cocaine and benzocaine.

        Types of local anesthesia

        There are two main types of local anesthetics depending on how they are applied.

        Topical anesthetics

        Topical anesthetics are applied directly to the skin or mucous membranes, such as the inside of the mouth, nose, and throat. They can also be applied to the surface of the eye. Topical anesthetics are marketed and applied in several ways:

        • Liquids
        • Creams
        • Gels
        • Vaporizers
        • Patches

        In some cases, the doctor may use a combination of local anesthetics to have a longer lasting effect long term.

        The following are examples of procedures using topical local anesthesia:

        • Apply or remove points
        • Prick with a needle
        • Intravenous insertion
        • Catheter insertion
        • Laser treatments
        • Cataract surgery
        • Endoscopy

        Most local anesthetics that we find in a drugstore are topical, compounds of benzocaine in many cases, and are used to manage the pain of:

        • Teeth, gums or canker sores
        • Open wound
        • Sore throat
        • minor burns
        • Poison ivy rash
        • bites
        • Hemorrhoids

        Injected anesthetics

        Local anesthetics can be given by injection. This type of anesthetic they are generally used for minor procedures in which the area of ​​intervention needs to be numbed rather than for pain management. Some of the procedures where local anesthesia is injected include:

        • Dental intervention, such as in root canal treatment.
        • Skin biopsy
        • Removal of a growth under the skin
        • Removal of moles or deep warts
        • Insertion of pacemakers
        • Diagnostic tests such as lumbar puncture or bone marrow biopsy

        The type of anesthesia needed for the particular case will vary depending on the specifics of the procedure and the patient’s own characteristics. For example, in the case of cataract surgery, this type of intervention can be performed both under topical anesthesia and by injection. Your doctor will determine the best type of anesthesia to apply based on the following factors.

        • The duration of the procedure
        • The size and location of the area to be numbed
        • If there is an underlying health problem that may affect the procedure
        • Medication taken by the patient

        How is it administered?

        The patient does not have to do much when preparing to administer local anesthesia; however, you should inform your doctor or anesthesiologist. any inconvenience that could affect both the effectiveness of the local anesthetic and the possibility of side effects. The following information the doctor should know about the patient before applying local anesthesia:

        • If there are any open sores near the affected area
        • If you are taking any type of medicine, especially blood thinners
        • If you have a bleeding disorder, such as hemophilia or Von Willebrand’s disease

        The patient will be given local anesthesia shortly before the start of the procedure, giving the anesthesia sufficient time to begin to take effect and perform the operation. for the duration of the numbness.

        It is likely that the operation will last a few minutes during which the patient should not feel any pain, although he may feel some sensations of pressure. in the intervention area. In case of pain, a higher dose of local anesthetic should be applied.

        Local anesthesia is usually applied for an hour, but the patient will notice slight numbness for a few more hours. As its effects wear off, the patient may notice tingling and spasms. The patient is advised to pay attention to the numb area as it is less noticeable and is more likely to sustain an injury without realizing it.

          Side effects of local anesthesia

          In general, local anesthetics are safe and do not cause side effects, with the exception of tickling and small spasms which may be noticed in the numb area after the operation. However, in the event that a higher than normal dose was given, the injection was made into a vein instead of a tissue or the patient may simply be more sensitive than average to the anesthetic, side effects the following are likely to occur:

          • Ringing in the ears
          • Light head
          • Numbness
          • Spasms
          • Metallic flavor

          In extremely rare cases where too much local anesthesia has been administered the following effects can be given:

          • Seizures

          • Low blood pressure
          • Slow heartbeat
          • Breathing problems

          There may also be an allergic reaction to the anesthetic, although this is a rare situation and research suggests that only 1% of the general population is allergic to local anesthetics.

          Bibliographical references

          • Tomoyasu, Y., Mukae, K., Suda, M., Hayashi, T., Ishii, M., Sakaguchi, M., Watanabe, Y., Jinzenji, A., Arai, Y., Higuchi, H., Maeda, S. and Miyawaki, T. (2011). Allergic reactions to local anesthetics in dental patients: analysis of intracutaneous tests and challenge. The Journal of Open Dentistry, 5, 146-149.
          • McLure, HA and Rubin, AP (2005). Review of local anesthetic agents. Minerva anestesiologica, 71 (3), 59-74.
          • Moore, PA and Hersh, EV (2010). Local anesthetics: pharmacology and toxicity. Dental Clinics of North America, 54 (4), 587-599.
          • Smith C. (1994). Pharmacology of local anesthetic agents. British Journal of Hospital Medicine, 52 (9), 455-460.
          • Lange, RA and Hillis, LD (2001). Cardiovascular complications of cocaine use. The New England Journal of Medicine, 345 (5), 351-358.

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