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A local anesthetic ( LA) is a medication that causes absence of all sense (including pain) in a specific body part without loss of consciousness, providing local anesthesia, 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.
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.
Medium Duration of Action and Medium Potency
High Duration and High Potency
They are used in various techniques of local anesthesia such as:
Some typical uses of conduction anesthesia for acute pain are:
| Labor pain | Epidural anesthesia, Pudendal nerve blocks |
| Postoperative pain | Peripheral nerve blocks, epidural anesthesia |
| Injury | Peripheral nerve blocks, intravenous regional anesthesia, epidural anesthesia |
| Dentistry | topical anesthesia (surface anesthesia), infiltration anesthesia and intraligamentary anesthesia during restorative operations such as fillings, crowns, and root canals, or extractions, and regional nerve blocks during extractions and surgeries |
| Podiatry (surgery of feet, ankles, and legs) | cutaneous anesthesia, , matricectomy, bunionectomy, hammertoe repair and various other podiatric procedures |
| Eye surgery | surface anesthesia with topical anesthetics or retrobulbar block during cataract removal or other ophthalmic procedures |
| Head and neck surgery (ENT operations) | infiltration anesthesia, field blocks, or peripheral nerve blocks, plexus anesthesia |
| Shoulder surgery Arm surgery | plexus anesthesia or intravenous regional anesthesia |
| Cardiac surgery (heart surgery) Pulmonary surgery (lung surgery) | epidural anesthesia combined with general anesthesia |
| Abdominal surgery | epidural anesthesia or spinal anesthesia, often combined with general anesthesia during inguinal hernia repair or other abdominal surgery |
| Gynecological surgery Obstetric surgery Urological surgery | spinal anesthesia or epidural anesthesia |
| Bone surgery and joint surgery of the pelvis, hip, and leg | spinal anaesthesia or epidural anesthesia, peripheral nerve blocks, or intravenous regional anesthesia |
| Skin surgery and peripheral vascular surgery | topical anesthesia, , peripheral nerve blocks, spinal anesthesia or epidural anesthesia |
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 endoscopy procedures such as bronchoscopy (visualization of the lower airways) or cystoscopy (visualization of the inner surface of the bladder)
The side effects of inferior alveolar nerve block include feeling tense, clenching of the fists and moaning. (2014). 9780867156157 ISBN 9780867156157
The duration of soft tissue anesthesia is longer than pulpal anesthesia and is often associated with difficulty eating, drinking and speaking.
There is risk of accidental damage to local blood vessels during injection of the local anesthetic solution. This is referred to as Hematoma and could result in pain, trismus, swelling and/or discolouration of the region. The density of tissues surrounding the injured vessels is an important factor for haematoma. There is greatest chance of this occurring in a posterior superior alveolar nerve block or in a pterygomandibular block.
Giving local anesthesia to patients with liver disease can have significant consequences. Thorough evaluation of the disease should be carried out to assess potential risk to the patient as in significant liver dysfunction, the half-life of amide local anesthetic agents may be drastically increased thus increasing the risk of overdose.
Local anesthetics and vasoconstrictors may be administered to pregnant patients however it is very important to be extra cautious when giving a pregnant patient any type of drug. Lidocaine can be safely used but bupivacaine and mepivacaine should be avoided. Consultation with the obstetrician is vital before administering any type of local anesthetic to a pregnant patient.
Symptoms may continue to improve for up to 18 months following injury.
On the other hand, fear of administration can also result in accelerated, shallow breathing, or hyperventilation. The patient may feel a tingling sensation in hands and feet or a sense of light-headedness and increased chest pressure.
Hence, it is crucial for the medical professional administrating the local anesthesia, especially in the form of an injection, to ensure that the patient is in a comfortable setting and has any potential fears alleviated in order to avoid these possible complications.
Initial symptoms of systemic toxicity include ringing in the ears (tinnitus), a metallic taste in the mouth, tingling or numbness of the mouth, dizziness and/or disorientation.
At higher concentrations, a relatively selective depression of inhibitory neurons results in cerebral excitation, which may lead to more advanced symptoms include motor twitching in the periphery followed by grand mal seizures. It is reported that seizures are more likely to occur when bupivacaine is used, particularly in combination with chloroprocaine.
A profound depression of brain functions may occur at even higher concentrations which may lead to coma, respiratory arrest, and death. Such tissue concentrations may be due to very high plasma levels after intravenous injection of a large dose.
Another possibility is direct exposure of the central nervous system through the cerebrospinal fluid, i.e., overdose in spinal anesthesia or accidental injection into the subarachnoid space in epidural anesthesia.
Cardiac toxicity associated with overdose of intravascular injection of local anesthetic is characterized by hypotension, atrioventricular conduction delay, idioventricular rhythms, and eventual cardiovascular collapse. Although all local anesthetics potentially shorten the myocardial refractory period, bupivacaine blocks the cardiac sodium channels, thereby making it most likely to precipitate malignant Heart arrhythmia. Even levobupivacaine and ropivacaine (single-enantiomer derivatives), developed to ameliorate cardiovascular side effects, still harbor the potential to disrupt cardiac function. Toxicity from anesthetic combinations is additive.
During pregnancy, it is not common for local anesthetics to have any adverse effect on the fetus. Despite this, risks of toxicity may be higher in pregnancy due to an increase in unbound fraction of local anesthetic and physiological changes increase the transfer of local anesthetic into the central nervous system. Hence, it is recommended that pregnant women use a lower dose of local anesthetic to reduce any potential complications.
Though most case reports to date have recorded most common use of Intralipid, other emulsions, such as Liposyn and Medialipid, have also been shown effective.
Ample supporting animal evidence and human case reports show successful use of lipid rescue in this way. In the UK, efforts have been made to publicize lipid rescue more widely. In 2010, lipid rescue had been officially promoted as a treatment of local anesthetic toxicity by the Association of Anaesthetists of Great Britain and Ireland. One published case has been reported of successful treatment of refractory cardiac arrest in bupropion and lamotrigine overdose using lipid emulsion.
The design of a 'homemade' lipid rescue kit has been described.
Although lipid rescue mechanism of action is not completely understood, the added lipid in the blood stream may act as a sink, allowing for the removal of lipophilic toxins from affected tissues. This theory is compatible with two studies on lipid rescue for clomipramine toxicity in rabbits and with a clinical report on the use of lipid rescue in veterinary medicine to treat a puppy with moxidectin toxicosis.
LAs are weak bases and are usually formulated as the hydrochloride salt to render them water-soluble. At a pH equal to the protonated base's pKa, the protonated (ionized) and unprotonated (unionized) forms of the molecule exist in equimolar amounts, but only the unprotonated base diffuses readily across cell membranes. Once inside the cell, the local anesthetic will be in equilibrium, with the formation of the protonated (ionized) form, which does not readily pass back out of the cell. This is referred to as "ion-trapping". In the protonated form, the molecule binds to the LA binding site on the inside of the ion channel near the cytoplasmic end. Most LAs work on the internal surface of the membrane - the drug has to penetrate the cell membrane, which is achieved best in the nonionised form. This is exemplified by the permanently ionised LA RAC 421-II which cannot diffusion across the cell membrane but, if injected into the cytosol of a nerve fibre, can induce NaKATPase blockage and anesthetic effects.
Acidosis such as caused by inflammation at a wound partly reduces the action of LAs. This is partly because most of the anesthetic is ionized and therefore unable to cross the cell membrane to reach its cytoplasmic-facing site of action on the sodium channel.
In general, autonomic fibers Type B fibers, small unmyelinated type C (pain sensation), and small myelinated Aδ fibers(pain and temperature sensations) are blocked before the larger myelinated Aγ, Aβ, and Aα fibers (mediating postural, touch, pressure, and motor information).
Injection of LAs is often painful. A number of methods can be used to decrease this pain, including buffering of the solution with bicarbonate and warming.
Clinical techniques include:
Dental-specific techniques include:
Dental needles are available in two lengths, short and long. As Vazirani–Akinosi is a local anesthetic technique which requires penetration of a significant thickness of soft tissues, a long needle is used. The needle is inserted into the soft tissue which covers the medial border of the mandibular ramus, in region of the inferior alveolar, lingual and mylohyoid nerves. The positioning of the bevel of the needle is very important as it must be positioned away from the bone of the mandibular ramus and instead towards the midline.
ILI utilization is expected to increase because dental patients prefer fewer soft tissue anesthesia and dentists aim to reduce administration of traditional inferior alveolar nerve block (INAB) for routine restorative procedures.
Injection methodology: The periodontal ligament space provides an accessible route to the cancellous alveolar bone, and the anesthetic reaches the pulpal nerve via natural perforation of intraoral bone tissue.
Advantages of ILI over INAB: rapid onset (within 30 seconds), small dosage required (0.2–1.0 mL), limited area of numbness, lower intrinsic risks such as neuropathy, hematoma, trismus/jaw sprain and self-inflicted periodontal tissue injury, as well as decreased cardiovascular disturbances. Its usage as a secondary or supplementary anesthesia on the mandible has reported a high success rate of above 90%.
Disadvantages: Risk of temporary periodontal tissue damage, likelihood of bacteriemia and endocarditis for at-risk populations, appropriate pressure and correct needle placement are imperative for anesthetic success, short duration of pulpal anesthesia limits the use of ILIs for several restorative procedures that require longer duration, postoperative discomfort, and injury on unerupted teeth such as enamel hypoplasia and defects.
Technique description:
Syringes:
Things to note:
Biophysical forces (pulsation of the maxillary artery, muscular function of jaw movement) and gravity will aid with the diffusion of anesthetic to fill the whole pterygomandibular space. All three oral sensory parts of the mandibular branch of the trigeminal nerve and other sensory nerves in the region will come in contact with the anesthetic and this reduces the need to anesthetise supplementary innervation.
In comparison to other regional block methods of anestheising the lower jaw, the Gow-Gates technique has a higher success rate in fully anesthetising the lower jaw. One study found that out of 1,200 patients receiving injections through the Gow-Gates technique, only 2 of them did not obtain complete anesthesia.
Amino esters are prone to producing allergic reactions, which may necessitate the use of an amide. The names of each locally clinical anesthetic have the suffix "-caine".
Most ester LAs are metabolized by pseudocholinesterase, while amide LAs are metabolized in the liver. This can be a factor in choosing an agent in patients with liver failure, although since cholinesterases are produced in the liver, physiologically (e.g. very young or very old individual) or pathologically (e.g. cirrhosis) impaired hepatic metabolism is also a consideration when using esters.
Sometimes, LAs are combined, e.g.:
LA solutions for injection are sometimes mixed with vasoconstrictors (combination drug) to increase the duration of local anesthesia by constricting the blood vessels, thereby safely concentrating the anesthetic agent for an extended duration, as well as reducing hemorrhage. Because the vasoconstrictor temporarily reduces the rate at which the systemic circulation removes the local anesthetic from the area of the injection, the maximum doses of LAs when combined with a vasoconstrictor is higher compared to the same LA without any vasoconstrictor. Occasionally, cocaine is administered for this purpose. Examples include:
Using LA with vasoconstrictor is safe in regions supplied by End artery.
The commonly held belief that LA with vasoconstrictor can cause necrosis in extremities such as the nose, ears, fingers, and toes (due to constriction of end arteries), is invalidated, since no case of necrosis has been reported since the introduction of commercial lidocaine with epinephrine in 1948.
Most naturally occurring local anesthetics with the exceptions of menthol, eugenol and cocaine are , and have the suffix -toxin in their names. Cocaine binds the intracellular side of the channels while saxitoxin, neosaxitoxin and tetrodotoxin bind to the extracellular side of sodium channels.
The invention of clinical use of local anaesthesia is credited to the Vienna School which included Sigmund Freud (1856-1939), Carl Koller (1857-1944) and Leopold Konigstein (1850–1942). They introduced local anaesthesia, using cocaine, through 'self-experimation' on their oral mucosa before introducing it to animal or human experimentation. The Vienna school first started using cocaine as local anaesthesia in ophthalmology and it was later incorporated into ophthalmologic practice. Dr. Halsted and Dr. Hall, in the United States in 1885 described an intraoral anesthetic technique of blocking the inferior alveolar nerve and the antero-superior dental nerve using 4% cocaine.
Shortly after the first use of cocaine for topical anesthesia, blocks on peripheral nerves were described. Brachial plexus anesthesia by percutaneous injection through axillary and supraclavicular approaches was developed in the early 20th century. The search for the most effective and least traumatic approach for plexus anesthesia and peripheral nerve blocks continues to this day. In recent decades, continuous regional anesthesia using catheters and automatic pumps has evolved as a method of pain therapy.
Intravenous regional anesthesia was first described by August Bier in 1908. This technique is still in use and is remarkably safe when drugs of low systemic toxicity such as prilocaine are used.
Spinal anesthesia was first used in 1885, but not introduced into clinical practice until 1899, when August Bier subjected himself to a clinical experiment in which he observed the anesthetic effect, but also the typical side effect of postpunctural headache. Within a few years, spinal anesthesia became widely used for surgical anesthesia and was accepted as a safe and effective technique. Although atraumatic (noncutting-tip) cannulae and modern drugs are used today, the technique has otherwise changed very little over many decades.
Epidural anesthesia by a caudal approach had been known in the early 20th century, but a well-defined technique using lumbar injection was not developed until 1921, when Fidel Pagés published his article "Anestesia Metamérica". This technique was popularized in the 1930s and 1940s by Achile Mario Dogliotti. With the advent of thin, flexible catheters, continuous infusion and repeated injections have become possible, making epidural anesthesia still a highly successful technique. Besides its many uses for surgery, epidural anesthesia is particularly popular in obstetrics for the treatment of labor pain.
Techniques
Local anesthetics can block almost every nerve between the peripheral nerve endings and the central nervous system. The most peripheral technique is topical anesthesia to the skin or other body surface. Small and large peripheral nerves can be anesthetized individually (peripheral nerve block) or in anatomic nerve bundles (plexus anesthesia). Spinal anesthesia and epidural anesthesia merge into the central nervous system.
Vazirani–Akinosi technique
The Vazirani–Akinosi technique is also known as the closed-mouth mandibular nerve block. It is mostly used in patients who have limited opening of the mandible or in those that have trismus; spasm of the muscles of mastication. The nerves which are anesthetised in this technique are the inferior alveolar, incisive, mental, lingual and mylohyoid nerves.
(2025). 9780323074131, Elsevier. ISBN 9780323074131
Intraligamentary Infiltration
Intraligamentary infiltration, also known as periodontal ligament injection or intraligamentary injection (ILI), is known as "the most universal of the supplemental injections". ILIs are usually administered when inferior alveolar nerve block techniques are inadequate or ineffective. ILIs are purposed for:
Gow-Gates Technique
Gow-Gates technique is used to provide anesthetics to the mandible of the patient's mouth. With the aid of extra and intraoral landmarks, the needle is injected into the intraoral latero-anterior surface of the condyle, steering clear below the insertion of the lateral pterygoid muscle. The extraoral landmarks used for this technique are the lower border of the ear tragus, corners of the mouth and the angulation of the tragus on the side of the face.
Types
Local anesthetic solutions for injection typically consist of:
One combination product of this type is used topically for surface anaesthesia, TAC (5–12% tetracaine,1/2000 (0.05%, 500 ppm, per mille) adrenaline, 4 or 10% cocaine).
Ester group
Amide group
Naturally derived
History
In Peru, the ancient Incas are believed to have used the leaves of the coca as a local anesthetic in addition to its stimulant properties. It was also used for slave payment and is thought to play a role in the subsequent destruction of Incas culture when Spaniards realized the effects of chewing the coca leaves and took advantage of it. Cocaine was first used as a local anesthetic in 1884. The search for a less toxic and less addictive substitute led to the development of the aminoester local anesthetics stovaine in 1903 and procaine in 1904. Since then, several synthetic local anesthetic drugs have been developed and put into clinical use, notably lidocaine in 1943, bupivacaine in 1957, and prilocaine in 1959.
See also
External links
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