How does local anesthesia work?
An overview of how local anesthesia works, the way it affects the nervous system.
In the form of sprays, gels, patches, injected... Local anesthesia is a type of intervention that can be done in multiple ways but all of them involve numbing a small region to avoid feeling pain.
Local anesthetics are used both at home, to treat a sore throat or gum discomfort, and in the offices of medical professionals, such as the dentist or dermatologist.
The mechanism of action of the drugs used in these procedures has the particularity that they affect the nerves, something that we are going to see in greater depth in the following section. how local anesthesia works in a summarized way.
How does local anesthesia work?
Local anesthesia consists of the use of drugs to temporarily numb a small part of the body.. This type of anesthesia is used before a minor medical procedure, such as a skin biopsy, and also in the dentist's office for the extraction of a tooth or application of a filling.
Unlike general anesthesia, local anesthesia does not put the patient to sleep.It does not cause the patient to fall asleep, intervening in the nerves in the area where it has been applied. To understand how it works, we must first review how the nervous system works in general.
As we already 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 nerve impulse transmission are mainly three: sodium (Na+), potassium (K+) and chlorine (Cl-).
When a stimulus hits a sensory cell, a nerve signal is produced.. This signal can be experienced in different ways such as, for example, in the form of temperature, pressure or, related to today's topic, pain.
For a nerve impulse to be generated, the electrical activation threshold of the neuron must be reached and, if it is reached, a process called depolarization takes place.
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, bringing Na+ into the nerve cell and causing K+ to leave, in a ratio of 3 to 2. In this way, the interior of the neuron becomes more positive, allowing the action potential to occur and thus the nerve impulse to be transmitted.
Having understood this, what does this have to do with how local anesthesia works? The truth is that it has a lot, since the mechanism of action of local anesthetic drugs directly affects the ability of the neurons in the intervened area to emit an impulse. Local anesthesia blocks the Na+ channels of the neuronal membrane, preventing this ion from entering the neuron and turning its interior positive. As 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 sufficient signals and, therefore, no pain is felt in the region.
Properties of these drugs
There are variety of local anesthetics and, therefore, their properties vary, although they all have in common being slightly alkaline. Because of this, these drugs do not work very well in acidic environments such as inflammation or infection.which is why they are not used in these medical conditions.
Chemically, local anesthetics are molecules consisting of an aromatic lipophilic ring linked to a hydrophilic group by an intermediate bond that can be of the ester or amide type. It is precisely the type of bond that can be found in the anesthetic that gives it one name or another, as well as influencing the way in which the substance is metabolized by the organism.
Amide-type anesthetics are metabolized in the liver, while ester-type anesthetics are metabolized by pseudocholinesterases in the blood. Ester anesthetics, once metabolized, give as a metabolite para-aminobenzoic acid which may cause Allergy in some people.
As a general rule, you can tell whether a local anesthetic is of 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 the one that forms the suffix -caine, such as lidocaine, mepivacaine, prilocaine or ropivacaine, while in the esters there is only the "i" of -caine, as we can see in chloroprocaine, procaine, cocaine and benzocaine.
Types of local anesthetics
There are two main types of local anesthetics depending on how they are applied.
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 multiple ways:
In some cases, the physician may use a combination of local anesthetics to have a longer lasting effect. long-term effect.
Examples of procedures in which topical local anesthetics are used include:
- Applying or removing stitches
- Needle stick
- Intravenous insertion
- Catheter insertion
- Laser treatments
- Cataract surgery
Most local anesthetics found in a pharmacy are topical, composed of benzocaine in many cases.They are composed of benzocaine in many cases, and are used to manage the pain of:
- Teeth, gums or mouth ulcers.
- Open wounds
- Sore throats
- Minor burns
- Poison Ivy Rash
- Bug bites
Local anesthetics can be administered by injection. These types of anesthetics are usually used for minor procedures where numbing of the surgical site is necessary rather than for pain management.. Among the procedures where local anesthesia is injected are:
- Dental intervention, 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 required for the particular case will vary depending on the specifics of the procedure. depending on the particularities of the procedure and the patient's own characteristics.. For example, in the case of cataract surgery, this type of surgery can be performed with either topical or injected anesthesia. The physician will determine the best type of anesthesia to use based on the following factors.
- The length of the procedure
- The size and location of the area that needs to be numbed.
- Whether there is an underlying health condition that may affect the procedure.
- Medication the patient is taking
How it is administered
The patient does not have to do much while preparing to have the local anesthesia administered; however, it is necessary to inform the physician or anesthesiologist of any inconvenience that could affect both the effectiveness of the local anesthetic and the possibility of side effects.. The information that the physician should know about the patient before applying local anesthesia is:
- If there are any open wounds near the affected area
- If you are taking any type of medication, especially anticoagulants.
- If you have a bleeding disorder, such as hemophilia or Von Willebrand's disease.
The patient will receive local anesthesia shortly before the procedure begins, giving the anesthetic enough time to take effect and perform the procedure for the duration of the numbness.
The operation will most likely take a few minutes, during which the patient should not feel any pain, although he/she may feel some sensations of pressure in the operated area. in the operated area. If pain is felt, a higher dose of local anesthetic will be necessary.
The local anesthetic is usually applied for one hour, but the patient will feel a slight numbness for a few more hours. As its effects wear off, the patient may notice tingling and spasms.. It is advisable for the patient to be careful with the numb area, since since it is not so noticeable, there is a greater probability of suffering an injury without realizing it.
Side effects of local anesthesia.
Generally, local anesthetics are safe and cause no side effects.except for tingling and small spasms that may be felt in the numb area after the procedure. However, in cases where a higher than normal dose has been administered, the injection has been made into a vein instead of tissue, or the patient is simply more sensitive than average to the anesthetic, the following side effects are likely to occur:
- Ringing in the ears
- Metallic taste
In extremely rare cases where there has been an administration of too high a dose of local anesthetic, the following effects may occur the following effects may occur:
- Low blood pressure
- Slowed heart rate
- Breathing problems
It is also possible to have an allergic reaction to the anesthetic, although this is a rare situation and research suggests that only 1% of the general population would be allergic to local anesthetics..
(Updated at Mar 28 / 2023)